Numerical study is carried out to investigate flapped delta wing low speed performance with coflo... more Numerical study is carried out to investigate flapped delta wing low speed performance with coflow jet (CFJ) flow control at Mach number of 0.1. Two delta wings formed by thin supersonic airfoils with aspect ratio of 2 and 0.67 and sweep angle of 53◦ and 63.5◦ are studied, but only the detailed results for the wing with aspect ratio of 2 are presented. The simulation is validated very well with the experiment. The flap has a constant chord along span and is 24% of the root chord. CFJ is applied in two ways: one on top of the main front part of the delta wing and the other is on the deflected flap. Both are effective, but the CFJ applied on the deflected flap is much more effective with flow attached up to the flap deflection angle of 60◦. It has substantially higher lift coefficient enhancement and lower CFJ power consumption for the same Cμ. With Cμ = 0.08 and CFJ applied on the flap, the delta wing with AR of 2 improves CL by 113.1% at a flap deflection angle of 60◦, whereas (CL/C...
This paper uses 3D CFD simulation to design the co-flow jet cascade secondary flow system. The CF... more This paper uses 3D CFD simulation to design the co-flow jet cascade secondary flow system. The CFD simulation located an area of massive separation from the suction side of the blade. This separation appears to be due to the end wall boundary layer on the top wall since the injection and suction jets are significantly less energetic near the top wall. It is mainly caused by the non-uniformity of the injection jet in the spanwise direction across the jet opening. Several internal duct designs were conducted with the best version being a 9port injection duct, which has a more uniform jet in streamwise direction and provides higher mass flow rate near the tunnel walls in an attempt to reduce wind tunnel wall affects. This design provides a flow which stays attached to the surface of the blade for nearly the entire span; the end wall effects still cause a minor separation in a small region near the top wall. The co-flow jet cascade designed allows for a diffusion factor of 0.74 at an in...
This paper numerically studies a lift enhancement approach for a supersonic thin airfoil with t/c... more This paper numerically studies a lift enhancement approach for a supersonic thin airfoil with t/c of 3.2% using Co-Flow Jet (CFJ) active flow control at Mach number of 0.1. The Reynolds averaged Navier-Stokes equations with Spalart-Allmaras turbulence model are solved with high order accuracy numerical schemes. The CFJ is first applied to the flapless airfoil. It is able to achieve a high lift coefficient of 2.12 at an angle of incidence of 18deg, 141.9% higher than the baseline airfoil, but at a very large CFJ power cost with the CFJ power coefficient of 3.06. By using a flap for the baseline and CFJ airfoil at zero angle of incidence, the lift coefficient can be increased much more efficiently than using a flapless airfoil. Two methods applying CFJ on the flapped airfoil are investigated: 1) using CFJ on the front main part of the flapped airfoil; 2) using CFJ on both the front part and on the flap. For the same momentum coefficient C µ of 0.08, the methods 2 achieves a high lift coefficient of 1.91, 42.5% higher than that of the method 1, with a CFJ power coefficient of 0.085, 7.6% lower than that of the method 1. The C L /C D and (C L /C D) c for the CFJ method 2 is 20 and 10.6, respectively. Compared with the baseline flapped airfoil with no flow control, the lift increase is 103% with a (C L /C D) c increase of 5.5%, which results in a productivity efficiency increase of 114.2%. Such a good aerodynamic performance is attributed to splitting the CFJ to two series CFJs in streamwise direction with C µ of 0.024 used in the front and 0.056 used on the flap. The front CFJ mitigates the separation bubble on the front part of the thin airfoil and energizes the flow, the rear CFJ attaches the flow efficiently in adverse pressure gradients. Even though the total C µ of 0.08 is the same for the CFJ method 1 and 2, each of the CFJ in the method 2 has a lower total pressure loss and thus requires lower total pressure ratio from the CFJ actuators, which reduces the total CFJ power required. Using two CFJs in series in the streamwise direction provides a high effectiveness and high efficiency lift enhancement method for supersonic thin airfoil. More study needs to be done to understand the interaction relationship between the two CFJs.
44th AIAA Aerospace Sciences Meeting and Exhibit, 2006
A CFD calculation strategy is developed to simulate 2D co-flow jet airfoil. The jet ducts reactio... more A CFD calculation strategy is developed to simulate 2D co-flow jet airfoil. The jet ducts reaction forces are added to the surface integral of pressure and shear stress to calculate the total lift and drag. The predicted lift and drag agree well with the experiment at low angle of attack(AoA) and deviate largely at high AoA. The stall AoA of the CFJ airfoil is predicted reasonably well. Details of the flow field results and comparison between the computation and experiment are given in the paper.
The three dimensional crossing shock waveturbulent boundary layer interaction caused by an asymme... more The three dimensional crossing shock waveturbulent boundary layer interaction caused by an asymmetric 7 0 11 0 double n was calculated by solving the Reynolds averaged Navier-Stokes equations with a full Reynolds Stress Equation model. An implicit approximate factorization method is used for the temporal integration. Roe's scheme is used for evaluation of the convective terms of the mean ow and Reynolds stress equations with a third order MUSCL-type differencing. The computed surface pressure is in good agreement with the experiment. The computed heat transfer coe cient shows a modest improvement compared with the previous results obtained using the k model with Chien's low Reynolds number correction. Both computations of the heat transfer display signi cant deviations form the experiment. Details of grid re nement studies are also presented.
34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 1998
layer interaction on the shoulder of the inlet centerbody and the entire inlet is brought to unst... more layer interaction on the shoulder of the inlet centerbody and the entire inlet is brought to unstart. The overall computed flow field phenomena agree qualitatively with the experimental observations. 1 Nomenclature Symbol Definition___________________ MOO Free Stream Mach Number P too Free Stream Total Pressure T too Free Stream Total Temperature Aa; grid point interval in axial direction Ar grid point interval in radial direction Arf (Aritir)/!/ 8 boundary layer thickness on center body R c radius at cowl leading edge t c characteristic time a angle of attack
A novel subsonic airfoil circulation augment technique using co-flow jet(CFJ) to achieve superior... more A novel subsonic airfoil circulation augment technique using co-flow jet(CFJ) to achieve superior aerodynamic performance for subsonic aircraft is proved numerically by CFD simulation. The advantages of co-flow jet airfoil include high lift at high angle of attack, ultra high C l /C d at cruise point, and low penalty to the overall cycle efficiency of the airframe-propulsion system. Unlike the conventional circulation control (CC) airfoil which is only suitable for landing and taking off, the CFJ airfoil can be used for the whole flying mission. No blunt leading and trailing edge is required so that the pressure drag is small. No moving parts are needed and make it easy to be implemented and weight less. The jet to enhance the circulation will be recirculated. Compared with the CC airfoil, the recirculating CFJ airfoil will significantly save fuel consumption because: 1) the power required to energize the jet is less; 2) no penalty to the jet engine thrust and efficiency due to the disposed jet mass flow since the jet mass flow is recirculated. For the NACA2415 airfoil studied, at low AOA with moderate momentum jet coefficient, the coflow jet airfoil will not only significantly enhance the lift, but also dramatically reduce the drag, or even generate the negative drag (thrust). The mechanism is that the coflow jet can control the pressure drag by filling the wake, and could generate negative pressure drag greater than the friction drag. This may allow the aircraft to cruise with very high aerodynamic efficiency. At high AOA, both the lift and the drag are significantly higher than the airfoil with no flow control, which may enhance the performance of taking off and landing within short distance.
44th AIAA Aerospace Sciences Meeting and Exhibit, 2006
*† ‡ § ** The wind tunnel tests reported in this paper demonstrate the ability of the co-flow jet... more *† ‡ § ** The wind tunnel tests reported in this paper demonstrate the ability of the co-flow jet airfoil to dramatically increase lift, stall margin, and drag reduction. Detailed velocity field measurements are reported for a baseline NACA0025 airfoil and two variants of the baseline which implement the co-flow jet. The first variant has an injection slot size of 0.65% of chord while the second has an injection slot size twice that size.
33rd Joint Propulsion Conference and Exhibit, 1997
A High Speed Civil Transport (HSCT) inlet at Mach 2 and angle of attack is simulated by using a 3... more A High Speed Civil Transport (HSCT) inlet at Mach 2 and angle of attack is simulated by using a 3D Navier-Stokes solver with the Baldwin-Lomax algebraic turbulence model. An extrapolation uniform mass bleed boundary condition for the slot bleed is successfully employed. For zero angle of attack and critical operation, the pressure distribution agrees well with the experiment. The location and intensity of the terminal shock, total pressure recovery are accurately computed. The angle of attack to cause the inlet unstart is accurately predicted. The mesh renement results are presented.
Propellers with forward sweep were studied in order to determine whether this type of sweep produ... more Propellers with forward sweep were studied in order to determine whether this type of sweep produces a more efficient propulsion source. The sweep effect is achieved solely by tangentially leaning the leading edge of the blades toward the direction of rotation. Eight 155mm (6.1") diameter propeller designs were created for testing; one straight blade, used for comparison, and seven swept blades using different sweep angles and configurations. Wind tunnel tests were conducted on all blades and CFD simulations were made for the straight blade as well as the best performing swept designs from the wind tunnel results. While efficiency values from wind tunnel tests and CFD simulations were not the same, the trends created in both were considered to be comparable. The general trend established shows that the swept blades not only have higher efficiencies but also have greater stall margins. Some speculated reasons for these advantages are given.
The unstart transient of a high-speed civil transport mixed compression axisymmetric inlet at Mac... more The unstart transient of a high-speed civil transport mixed compression axisymmetric inlet at Mach 2 and 2-deg angle of attack was investigated numerically by using a three-dimensional time-accurate Navier‐Stokes solver. The Baldwin ‐Lomax algebraic turbulence model and an extrapolation uniform mass bleed boundary condition for the slot bleed were employed. It is observed that, when an angle of attack is imposed, the e ow on the leeward side has a stronger compression than that at zero angle of attack. The strong compression reduces the Mach number upstream of the terminal shock and therefore makes the shock move upstream e rst on the leeward side. The initial shock motion starts with the bifurcation of the terminal shock. The lower part of the split shock is stable because of the centerbody bleed, whereas the top part of the shock continues to travel upstream. When the terminal shock on the leeward side passes the bleed region, a separation is induced by the shock /boundary-layer interaction on the shoulder of the inlet centerbody, and the entire inlet is brought to unstart. The overall computed e owe eld phenomena agree qualitatively with the experimental observations.
A multilevel design strategy for supersonic missile inlet design is developed. The multilevel des... more A multilevel design strategy for supersonic missile inlet design is developed. The multilevel design strategy combines an ef cient simple physical model analysis tool and a sophisticated computational uid dynamics (CFD) Navier-Stokes analysis tool. The ef cient simple analysis tool is incorporated into the optimization loop, and the sophisticated CFD analysis tool is used to verify, select, and lter the nal design. The genetic algorithms and multistart gradient line search optimizers are used to search the nonsmooth design space. A geometry model for the supersonic missile inlet is developed. A supersonic missile inlet that starts at Mach 2.6 and cruises at Mach 4 was designed. Signi cant improvement of the inlet total pressure recovery has been obtained. Detailed ow eld analysis is also presented.
A control volume analysis is presented in this paper to analyze the jet effect on the coflow jet ... more A control volume analysis is presented in this paper to analyze the jet effect on the coflow jet airfoil with injection and suction and on the airfoil with injection only. The formulations to calculate the duct's reactionary forces that must be included for the lift and drag calculation are given. The computational fluid dynamics solutions based on the Reynolds-averaged Navier-Stokes model are used to provide the breakdowns of lift and drag contributions from the airfoil surface force integral and jet duct's reactionary forces. The results are compared with experiment for validation. The duct reactionary forces are also validated with the result of a 3-D computational fluid dynamics calculation of the complete airfoil with jet ducts and wind tunnel walls. The study indicates that the suction occurring on the airfoil suction surface of the coflow jet airfoil is more beneficial than the suction occurring through the engine inlet such as the airfoil with injection only. For the airfoil with injection only, the drag actually acted on the aircraft, or the equivalent drag, is significantly larger than the drag measured by the wind tunnel balance due to the ram drag and captured area drag when the jet is drawn from the freestream. For a coflow jet airfoil, the drag measured by the wind tunnel balance is the actual 2-D drag that the aircraft will experience. A coflow jet airfoil does not have the ram drag and captured area drag. For a coflow jet airfoil, the suction penalty is offset by the significant circulation enhancement. The coflow jet airfoil with both injection and suction yields stronger mixing, larger circulation, more filled wake, higher stall angle of attack, less drag, and lower energy expenditure.
A high-speed civil transport inlet at Mach 2 and angle of attack is simulated by using a three-di... more A high-speed civil transport inlet at Mach 2 and angle of attack is simulated by using a three-dimensional Navier‐Stokes solver with the Baldwin ‐Lomax algebraic turbulence model. An extrapolation uniform mass bleed boundary condition for the slot bleed is successfully employed. At zero angle of attack and critical operation, the computational pressure distribution agrees well with the experiment. The location and intensity of the terminal shock and the total pressure recovery are accurately computed. The predicted steady-state distortion deviates from the experiment. The computed maximum angle of attack that the inlet can sustain before unstart is in good agreement with the experiment. Mesh ree nement results are presented.
The three-dimensional crossing shock wave/turbulent-boundary-layer interaction caused by an asymm... more The three-dimensional crossing shock wave/turbulent-boundary-layer interaction caused by an asymmetric 7 x 11-deg double fin with incoming Mach number 3.95 was simulated using the Reynolds-averaged Navier-Stokes equations with a full Reynolds stress equation turbulence model. An implicit approximate factorization method is used for the temporal integration. Roe's scheme is used for evaluation of the convective terms of the mean flow and Reynolds stress equations with a third-order MUSCL-type differencing. The computed surface pressure is in good agreement with the experiment. The computed heat transfer coefficient shows a modest improvement compared with previous results obtained using the k-c model with Chien's low-Reynolds-number correction. Both computations of the heat transfer display significant deviations from experiment. Tests of the grid refinement, different upstream boundary-layer profiles, and different isothermal wall temperature also are presented.
This paper numerically studies the Mach number effect on cruise performance of a Co-Flow Jet (CFJ... more This paper numerically studies the Mach number effect on cruise performance of a Co-Flow Jet (CFJ) general aviation (GA) airplane at freestream Mach number of 0.15, 0.30, and 0.46 with an aspect ratio of 21.3. An optimized CFJ-NACA-6421 airfoil is used for the CFJ wing. The advantages of using a thick airfoil are two folds: 1) higher cruise lift coefficient; 2) lighter weight. The numerical simulations employ the intensively validated in house FASIP CFD code, which utilizes a 3D RANS solver with Spalart-Allmaras (S-A) turbulence model, 3rd order WENO scheme for the inviscid fluxes, and 2nd order central differencing for the viscous terms. Two constant C µ of 0.03 and 0.04 are studied to examine the effect on the aircraft cruise performance. The angle of attack (AoA) is held at 5 • corresponding to the optimal aerodynamic and productivity efficiency in the previous study for the wing performance at different Mach number. At C µ of 0.03, the flow is very well attached for Mach 0.15, which gives the highest pure lift to drag ratio C L /C D , the corrected aerodynamic efficiency with CFJ power coefficient included (C L /C D) c , and the productivity efficiency (C 2 L /C D) c. When the Mach number is increased to 0.46, the lift coefficient is increased by 8.6% from 1.16 to 1.26 due to the compressibility effect, but all the three aerodynamic performance parameters, C L /C D , (C L /C D) c , and (C 2 L /C D) c drop substantially. The reason is that the a flow separation at the wing-fuselage junction occurs. The drag coefficient is significantly increased by 67% when the Mach number is increased form 0.15 to 0.46 due to the flow separation, higher skin friction drag, and higher induced drag. When the C µ is increased to 0.04, the wing-fuselage junction flow separation is removed. The CFJ power coefficient is increased by 33%, but remains at a very low level due to the low energy expenditure feature of the CFJ flow control. The C L /C D , (C L /C D) c , and (C 2 L /C D) c are significantly increased by 21.3%, 10.7%, and 19.8% respectively. In other words, the CFJ power increased due to C µ of 0.04 at Mach 0.46 is converted to more system efficiency gain reflected by enhanced (C L /C D) c and (C 2 L /C D) c , which include the CFJ power coefficient. The system efficiency gains are attributed to the increased C L and substantially reduced C D due to the removed flow separation at low CFJ energy expenditure. Nomenclature CF J Co-flow jet AoA Angle of attack * Graduate Student † Professor, AIAA associate Fellow ‡ Simulation Specialist, Ph.D.
This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantif... more This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantify lift enhancement, drag reduction, and energy expenditure at a Mach number range from 0.03 to 0.4. The jet momentum coefficient is held constant at 0.08, and the angle of attack varies from 0 to 30 deg. The two-dimensional flow is simulated using a Reynolds-averaged Navier-Stokes solver with a fifth-order-weighted essentially non-oscillatory scheme for the inviscid flux and a fourth-order central differencing for the viscous terms. Turbulence is simulated with the one equation Spalart-Allmaras model. The predicted coflow jet pumping power has an excellent agreement with the experiment. At a constant Mach number, the power coefficient is decreased when the angle of attack is increased from 0 to 15 deg. When the Mach number is increased from 0.03 to 0.3, the suction effect behind the airfoil leading edge is further augmented due to the compressibility effect. This results in an increased maximum lift coefficient and reduced power coefficient at the higher Mach number because of the lower jet-injection pumping pressure required. At Mach 0.4, the lift coefficient is further improved. However as the angle of attack is increased, a λ shock wave interrupts the jet and triggers the boundary layer separation with increased drag and power coefficient. A corrected aerodynamic efficiency that includes the coflow-jet pumping power is introduced. Because of the high lift coefficient and low coflowjet power required, the coflow-jet airfoil in this study achieves a comparable peak aerodynamic efficiency to the baseline airfoil, but the lift coefficient at peak efficiency is substantially increased by 120%. This study indicates that the coflow-jet airfoil is not only able to achieve very high maximum lift coefficient, but also able to improve cruise performance at low angle of attack when the flow is benign.
Numerical study is carried out to investigate flapped delta wing low speed performance with coflo... more Numerical study is carried out to investigate flapped delta wing low speed performance with coflow jet (CFJ) flow control at Mach number of 0.1. Two delta wings formed by thin supersonic airfoils with aspect ratio of 2 and 0.67 and sweep angle of 53◦ and 63.5◦ are studied, but only the detailed results for the wing with aspect ratio of 2 are presented. The simulation is validated very well with the experiment. The flap has a constant chord along span and is 24% of the root chord. CFJ is applied in two ways: one on top of the main front part of the delta wing and the other is on the deflected flap. Both are effective, but the CFJ applied on the deflected flap is much more effective with flow attached up to the flap deflection angle of 60◦. It has substantially higher lift coefficient enhancement and lower CFJ power consumption for the same Cμ. With Cμ = 0.08 and CFJ applied on the flap, the delta wing with AR of 2 improves CL by 113.1% at a flap deflection angle of 60◦, whereas (CL/C...
This paper uses 3D CFD simulation to design the co-flow jet cascade secondary flow system. The CF... more This paper uses 3D CFD simulation to design the co-flow jet cascade secondary flow system. The CFD simulation located an area of massive separation from the suction side of the blade. This separation appears to be due to the end wall boundary layer on the top wall since the injection and suction jets are significantly less energetic near the top wall. It is mainly caused by the non-uniformity of the injection jet in the spanwise direction across the jet opening. Several internal duct designs were conducted with the best version being a 9port injection duct, which has a more uniform jet in streamwise direction and provides higher mass flow rate near the tunnel walls in an attempt to reduce wind tunnel wall affects. This design provides a flow which stays attached to the surface of the blade for nearly the entire span; the end wall effects still cause a minor separation in a small region near the top wall. The co-flow jet cascade designed allows for a diffusion factor of 0.74 at an in...
This paper numerically studies a lift enhancement approach for a supersonic thin airfoil with t/c... more This paper numerically studies a lift enhancement approach for a supersonic thin airfoil with t/c of 3.2% using Co-Flow Jet (CFJ) active flow control at Mach number of 0.1. The Reynolds averaged Navier-Stokes equations with Spalart-Allmaras turbulence model are solved with high order accuracy numerical schemes. The CFJ is first applied to the flapless airfoil. It is able to achieve a high lift coefficient of 2.12 at an angle of incidence of 18deg, 141.9% higher than the baseline airfoil, but at a very large CFJ power cost with the CFJ power coefficient of 3.06. By using a flap for the baseline and CFJ airfoil at zero angle of incidence, the lift coefficient can be increased much more efficiently than using a flapless airfoil. Two methods applying CFJ on the flapped airfoil are investigated: 1) using CFJ on the front main part of the flapped airfoil; 2) using CFJ on both the front part and on the flap. For the same momentum coefficient C µ of 0.08, the methods 2 achieves a high lift coefficient of 1.91, 42.5% higher than that of the method 1, with a CFJ power coefficient of 0.085, 7.6% lower than that of the method 1. The C L /C D and (C L /C D) c for the CFJ method 2 is 20 and 10.6, respectively. Compared with the baseline flapped airfoil with no flow control, the lift increase is 103% with a (C L /C D) c increase of 5.5%, which results in a productivity efficiency increase of 114.2%. Such a good aerodynamic performance is attributed to splitting the CFJ to two series CFJs in streamwise direction with C µ of 0.024 used in the front and 0.056 used on the flap. The front CFJ mitigates the separation bubble on the front part of the thin airfoil and energizes the flow, the rear CFJ attaches the flow efficiently in adverse pressure gradients. Even though the total C µ of 0.08 is the same for the CFJ method 1 and 2, each of the CFJ in the method 2 has a lower total pressure loss and thus requires lower total pressure ratio from the CFJ actuators, which reduces the total CFJ power required. Using two CFJs in series in the streamwise direction provides a high effectiveness and high efficiency lift enhancement method for supersonic thin airfoil. More study needs to be done to understand the interaction relationship between the two CFJs.
44th AIAA Aerospace Sciences Meeting and Exhibit, 2006
A CFD calculation strategy is developed to simulate 2D co-flow jet airfoil. The jet ducts reactio... more A CFD calculation strategy is developed to simulate 2D co-flow jet airfoil. The jet ducts reaction forces are added to the surface integral of pressure and shear stress to calculate the total lift and drag. The predicted lift and drag agree well with the experiment at low angle of attack(AoA) and deviate largely at high AoA. The stall AoA of the CFJ airfoil is predicted reasonably well. Details of the flow field results and comparison between the computation and experiment are given in the paper.
The three dimensional crossing shock waveturbulent boundary layer interaction caused by an asymme... more The three dimensional crossing shock waveturbulent boundary layer interaction caused by an asymmetric 7 0 11 0 double n was calculated by solving the Reynolds averaged Navier-Stokes equations with a full Reynolds Stress Equation model. An implicit approximate factorization method is used for the temporal integration. Roe's scheme is used for evaluation of the convective terms of the mean ow and Reynolds stress equations with a third order MUSCL-type differencing. The computed surface pressure is in good agreement with the experiment. The computed heat transfer coe cient shows a modest improvement compared with the previous results obtained using the k model with Chien's low Reynolds number correction. Both computations of the heat transfer display signi cant deviations form the experiment. Details of grid re nement studies are also presented.
34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 1998
layer interaction on the shoulder of the inlet centerbody and the entire inlet is brought to unst... more layer interaction on the shoulder of the inlet centerbody and the entire inlet is brought to unstart. The overall computed flow field phenomena agree qualitatively with the experimental observations. 1 Nomenclature Symbol Definition___________________ MOO Free Stream Mach Number P too Free Stream Total Pressure T too Free Stream Total Temperature Aa; grid point interval in axial direction Ar grid point interval in radial direction Arf (Aritir)/!/ 8 boundary layer thickness on center body R c radius at cowl leading edge t c characteristic time a angle of attack
A novel subsonic airfoil circulation augment technique using co-flow jet(CFJ) to achieve superior... more A novel subsonic airfoil circulation augment technique using co-flow jet(CFJ) to achieve superior aerodynamic performance for subsonic aircraft is proved numerically by CFD simulation. The advantages of co-flow jet airfoil include high lift at high angle of attack, ultra high C l /C d at cruise point, and low penalty to the overall cycle efficiency of the airframe-propulsion system. Unlike the conventional circulation control (CC) airfoil which is only suitable for landing and taking off, the CFJ airfoil can be used for the whole flying mission. No blunt leading and trailing edge is required so that the pressure drag is small. No moving parts are needed and make it easy to be implemented and weight less. The jet to enhance the circulation will be recirculated. Compared with the CC airfoil, the recirculating CFJ airfoil will significantly save fuel consumption because: 1) the power required to energize the jet is less; 2) no penalty to the jet engine thrust and efficiency due to the disposed jet mass flow since the jet mass flow is recirculated. For the NACA2415 airfoil studied, at low AOA with moderate momentum jet coefficient, the coflow jet airfoil will not only significantly enhance the lift, but also dramatically reduce the drag, or even generate the negative drag (thrust). The mechanism is that the coflow jet can control the pressure drag by filling the wake, and could generate negative pressure drag greater than the friction drag. This may allow the aircraft to cruise with very high aerodynamic efficiency. At high AOA, both the lift and the drag are significantly higher than the airfoil with no flow control, which may enhance the performance of taking off and landing within short distance.
44th AIAA Aerospace Sciences Meeting and Exhibit, 2006
*† ‡ § ** The wind tunnel tests reported in this paper demonstrate the ability of the co-flow jet... more *† ‡ § ** The wind tunnel tests reported in this paper demonstrate the ability of the co-flow jet airfoil to dramatically increase lift, stall margin, and drag reduction. Detailed velocity field measurements are reported for a baseline NACA0025 airfoil and two variants of the baseline which implement the co-flow jet. The first variant has an injection slot size of 0.65% of chord while the second has an injection slot size twice that size.
33rd Joint Propulsion Conference and Exhibit, 1997
A High Speed Civil Transport (HSCT) inlet at Mach 2 and angle of attack is simulated by using a 3... more A High Speed Civil Transport (HSCT) inlet at Mach 2 and angle of attack is simulated by using a 3D Navier-Stokes solver with the Baldwin-Lomax algebraic turbulence model. An extrapolation uniform mass bleed boundary condition for the slot bleed is successfully employed. For zero angle of attack and critical operation, the pressure distribution agrees well with the experiment. The location and intensity of the terminal shock, total pressure recovery are accurately computed. The angle of attack to cause the inlet unstart is accurately predicted. The mesh renement results are presented.
Propellers with forward sweep were studied in order to determine whether this type of sweep produ... more Propellers with forward sweep were studied in order to determine whether this type of sweep produces a more efficient propulsion source. The sweep effect is achieved solely by tangentially leaning the leading edge of the blades toward the direction of rotation. Eight 155mm (6.1") diameter propeller designs were created for testing; one straight blade, used for comparison, and seven swept blades using different sweep angles and configurations. Wind tunnel tests were conducted on all blades and CFD simulations were made for the straight blade as well as the best performing swept designs from the wind tunnel results. While efficiency values from wind tunnel tests and CFD simulations were not the same, the trends created in both were considered to be comparable. The general trend established shows that the swept blades not only have higher efficiencies but also have greater stall margins. Some speculated reasons for these advantages are given.
The unstart transient of a high-speed civil transport mixed compression axisymmetric inlet at Mac... more The unstart transient of a high-speed civil transport mixed compression axisymmetric inlet at Mach 2 and 2-deg angle of attack was investigated numerically by using a three-dimensional time-accurate Navier‐Stokes solver. The Baldwin ‐Lomax algebraic turbulence model and an extrapolation uniform mass bleed boundary condition for the slot bleed were employed. It is observed that, when an angle of attack is imposed, the e ow on the leeward side has a stronger compression than that at zero angle of attack. The strong compression reduces the Mach number upstream of the terminal shock and therefore makes the shock move upstream e rst on the leeward side. The initial shock motion starts with the bifurcation of the terminal shock. The lower part of the split shock is stable because of the centerbody bleed, whereas the top part of the shock continues to travel upstream. When the terminal shock on the leeward side passes the bleed region, a separation is induced by the shock /boundary-layer interaction on the shoulder of the inlet centerbody, and the entire inlet is brought to unstart. The overall computed e owe eld phenomena agree qualitatively with the experimental observations.
A multilevel design strategy for supersonic missile inlet design is developed. The multilevel des... more A multilevel design strategy for supersonic missile inlet design is developed. The multilevel design strategy combines an ef cient simple physical model analysis tool and a sophisticated computational uid dynamics (CFD) Navier-Stokes analysis tool. The ef cient simple analysis tool is incorporated into the optimization loop, and the sophisticated CFD analysis tool is used to verify, select, and lter the nal design. The genetic algorithms and multistart gradient line search optimizers are used to search the nonsmooth design space. A geometry model for the supersonic missile inlet is developed. A supersonic missile inlet that starts at Mach 2.6 and cruises at Mach 4 was designed. Signi cant improvement of the inlet total pressure recovery has been obtained. Detailed ow eld analysis is also presented.
A control volume analysis is presented in this paper to analyze the jet effect on the coflow jet ... more A control volume analysis is presented in this paper to analyze the jet effect on the coflow jet airfoil with injection and suction and on the airfoil with injection only. The formulations to calculate the duct's reactionary forces that must be included for the lift and drag calculation are given. The computational fluid dynamics solutions based on the Reynolds-averaged Navier-Stokes model are used to provide the breakdowns of lift and drag contributions from the airfoil surface force integral and jet duct's reactionary forces. The results are compared with experiment for validation. The duct reactionary forces are also validated with the result of a 3-D computational fluid dynamics calculation of the complete airfoil with jet ducts and wind tunnel walls. The study indicates that the suction occurring on the airfoil suction surface of the coflow jet airfoil is more beneficial than the suction occurring through the engine inlet such as the airfoil with injection only. For the airfoil with injection only, the drag actually acted on the aircraft, or the equivalent drag, is significantly larger than the drag measured by the wind tunnel balance due to the ram drag and captured area drag when the jet is drawn from the freestream. For a coflow jet airfoil, the drag measured by the wind tunnel balance is the actual 2-D drag that the aircraft will experience. A coflow jet airfoil does not have the ram drag and captured area drag. For a coflow jet airfoil, the suction penalty is offset by the significant circulation enhancement. The coflow jet airfoil with both injection and suction yields stronger mixing, larger circulation, more filled wake, higher stall angle of attack, less drag, and lower energy expenditure.
A high-speed civil transport inlet at Mach 2 and angle of attack is simulated by using a three-di... more A high-speed civil transport inlet at Mach 2 and angle of attack is simulated by using a three-dimensional Navier‐Stokes solver with the Baldwin ‐Lomax algebraic turbulence model. An extrapolation uniform mass bleed boundary condition for the slot bleed is successfully employed. At zero angle of attack and critical operation, the computational pressure distribution agrees well with the experiment. The location and intensity of the terminal shock and the total pressure recovery are accurately computed. The predicted steady-state distortion deviates from the experiment. The computed maximum angle of attack that the inlet can sustain before unstart is in good agreement with the experiment. Mesh ree nement results are presented.
The three-dimensional crossing shock wave/turbulent-boundary-layer interaction caused by an asymm... more The three-dimensional crossing shock wave/turbulent-boundary-layer interaction caused by an asymmetric 7 x 11-deg double fin with incoming Mach number 3.95 was simulated using the Reynolds-averaged Navier-Stokes equations with a full Reynolds stress equation turbulence model. An implicit approximate factorization method is used for the temporal integration. Roe's scheme is used for evaluation of the convective terms of the mean flow and Reynolds stress equations with a third-order MUSCL-type differencing. The computed surface pressure is in good agreement with the experiment. The computed heat transfer coefficient shows a modest improvement compared with previous results obtained using the k-c model with Chien's low-Reynolds-number correction. Both computations of the heat transfer display significant deviations from experiment. Tests of the grid refinement, different upstream boundary-layer profiles, and different isothermal wall temperature also are presented.
This paper numerically studies the Mach number effect on cruise performance of a Co-Flow Jet (CFJ... more This paper numerically studies the Mach number effect on cruise performance of a Co-Flow Jet (CFJ) general aviation (GA) airplane at freestream Mach number of 0.15, 0.30, and 0.46 with an aspect ratio of 21.3. An optimized CFJ-NACA-6421 airfoil is used for the CFJ wing. The advantages of using a thick airfoil are two folds: 1) higher cruise lift coefficient; 2) lighter weight. The numerical simulations employ the intensively validated in house FASIP CFD code, which utilizes a 3D RANS solver with Spalart-Allmaras (S-A) turbulence model, 3rd order WENO scheme for the inviscid fluxes, and 2nd order central differencing for the viscous terms. Two constant C µ of 0.03 and 0.04 are studied to examine the effect on the aircraft cruise performance. The angle of attack (AoA) is held at 5 • corresponding to the optimal aerodynamic and productivity efficiency in the previous study for the wing performance at different Mach number. At C µ of 0.03, the flow is very well attached for Mach 0.15, which gives the highest pure lift to drag ratio C L /C D , the corrected aerodynamic efficiency with CFJ power coefficient included (C L /C D) c , and the productivity efficiency (C 2 L /C D) c. When the Mach number is increased to 0.46, the lift coefficient is increased by 8.6% from 1.16 to 1.26 due to the compressibility effect, but all the three aerodynamic performance parameters, C L /C D , (C L /C D) c , and (C 2 L /C D) c drop substantially. The reason is that the a flow separation at the wing-fuselage junction occurs. The drag coefficient is significantly increased by 67% when the Mach number is increased form 0.15 to 0.46 due to the flow separation, higher skin friction drag, and higher induced drag. When the C µ is increased to 0.04, the wing-fuselage junction flow separation is removed. The CFJ power coefficient is increased by 33%, but remains at a very low level due to the low energy expenditure feature of the CFJ flow control. The C L /C D , (C L /C D) c , and (C 2 L /C D) c are significantly increased by 21.3%, 10.7%, and 19.8% respectively. In other words, the CFJ power increased due to C µ of 0.04 at Mach 0.46 is converted to more system efficiency gain reflected by enhanced (C L /C D) c and (C 2 L /C D) c , which include the CFJ power coefficient. The system efficiency gains are attributed to the increased C L and substantially reduced C D due to the removed flow separation at low CFJ energy expenditure. Nomenclature CF J Co-flow jet AoA Angle of attack * Graduate Student † Professor, AIAA associate Fellow ‡ Simulation Specialist, Ph.D.
This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantif... more This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantify lift enhancement, drag reduction, and energy expenditure at a Mach number range from 0.03 to 0.4. The jet momentum coefficient is held constant at 0.08, and the angle of attack varies from 0 to 30 deg. The two-dimensional flow is simulated using a Reynolds-averaged Navier-Stokes solver with a fifth-order-weighted essentially non-oscillatory scheme for the inviscid flux and a fourth-order central differencing for the viscous terms. Turbulence is simulated with the one equation Spalart-Allmaras model. The predicted coflow jet pumping power has an excellent agreement with the experiment. At a constant Mach number, the power coefficient is decreased when the angle of attack is increased from 0 to 15 deg. When the Mach number is increased from 0.03 to 0.3, the suction effect behind the airfoil leading edge is further augmented due to the compressibility effect. This results in an increased maximum lift coefficient and reduced power coefficient at the higher Mach number because of the lower jet-injection pumping pressure required. At Mach 0.4, the lift coefficient is further improved. However as the angle of attack is increased, a λ shock wave interrupts the jet and triggers the boundary layer separation with increased drag and power coefficient. A corrected aerodynamic efficiency that includes the coflow-jet pumping power is introduced. Because of the high lift coefficient and low coflowjet power required, the coflow-jet airfoil in this study achieves a comparable peak aerodynamic efficiency to the baseline airfoil, but the lift coefficient at peak efficiency is substantially increased by 120%. This study indicates that the coflow-jet airfoil is not only able to achieve very high maximum lift coefficient, but also able to improve cruise performance at low angle of attack when the flow is benign.
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Papers by Ge-cheng Zha