Turbulence Modeling S and Applications to Aerospike Plug Nozzle

2003

Computational Fluid Dynamics (CFD) analyses of axisymmetric circular-arc boattail nozzles have been completed in support of NASA's Next Generation Launch Technology Program to investigate the effects of high-speed nozzle geometries on the nozzle internal flow and the surrounding boattail regions. These computations span the very difficult transonic flight regime, with shock-induced separations and strong adverse pressure gradients. External afterbody and internal nozzle pressure distributions computed with the Wind code are compared with experimental data. A range of turbulence models were examined in Wind, including an Explicit Algebraic Stress model (EASM). Computations on two nozzle geometries have been completed at freestream Mach numbers ranging from 0.6 to 0.9, driven by nozzle pressure ratios (NPR) ranging from 2.9 to 5. Results obtained on converging-only geometry indicate reasonable agreement to experimental data, with the EASM and Shear Stress Transport (SST) turbulence models providing the best agreement. Calculations completed on a converging-diverging geometry involving large-scale internal flow separation did not converge to a true steady-state solution when run with variable timestepping (steadystate). Calculations obtained using constant timestepping (time-accurate) indicate less variations in flow properties compared with steady-state solutions. This failure to converge to a steady-state solution was found to be the result of difficulties in using variable time-stepping with large-scale separations present in the flow. Nevertheless, time-averaged boattail surface pressure coefficient and internal nozzle pressures show fairly good agreement with experimental data. The SST turbulence model demonstrates the best overall agreement with experimental data.

IOP Conference Series: Materials Science and Engineering

Aerospike nozzles have been a spinoff the plug nozzle alternative for propulsion systems that require adaptation for outside pressure variations. Their capacity to adapt their aerodynamics without the need of moving parts makes them very interesting for space launching vehicles. Conventional Laval nozzles have to trade-off performance as they cross the atmosphere from sea level to their maximum altitude. In this study, the flow simulation is carried out for full and truncated nozzle. Three cases for the truncated length are chosen: 40%, 50% and 60% plug in different working conditions. In over-expansion conditions, with the increase of plug truncation a loss of thrust is observed, compared with the under-expansion conditions, were the nozzle truncation has a negligible effect. CFD analysis shows which plug truncation is giving the optimum performances and how great is the influence of altitude and temperature on this type of propulsion system.

8th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, 1998

Plug nozzles have received renewed attention in the frame of future launcher developments. Their use appears particularly convenient for Single Stage to Orbit vehicles, because of the overall improvement in performance and also of their possible good integration with the vehicle shape. Nevertheless, a better understanding of the phenomena that take place is necessary, in order to evaluate accurately their behavior. The numerical and experimental analysis of two linear plug nozzle models, performed for different truncation lengths, has allowed to emphasize the critical points of the design. Moreover, the comparisons of numerical and experimental data indicate limitations and expectations for either approach to be used for analyzing their behavior.

International Journal of Engineering & Technology, 2018

A numerical simulation was carried out to compare various turbulence models simulating axisymmetric nozzle flow past suddenly expanded ducts. The simulations were done for L/D = 10. The convergent-divergent nozzle has been modeled and simulated using the turbulence models: The Standard k-ε model, The Standard k-ω model and The SST k-ω model. Numerical simulations were done for Mach numbers 1.87, 2.2, and 2.58 and the nozzles were operated for NPRs in the range from 3 to 11. From the numerical analysis it is apparent that for a given Mach number and effect of NPR will result in maximum gain or loss of pressure. Numerical results are in good agreement with the experimental results.

2021

Aerospike nozzles are now-a-days one of the most emerging topics for research and development work leading for the futuristic goals of an aerospace industries and organizations. They are indulging in a class of elevation balancing nozzle engines. These nozzle engines are basically constructed for single-stage-to-orbit (SSTO) as well as foremost engine for space vehicles. These nozzles are about 75% shorter than the standard nozzle for similar expansion ratios. Aerodynamic thrust variation and performances play a key role in estimating forces along with the injected flow and their characteristics. This review paper deals with the aerodynamics characterization, its properties at different conditions in addition with the performance analysis of the aerospike

Science Vision - A scientific journal of COMSATS, 2014

The paper presents an aerodynamic design of a simplified linear aerospike nozzle and its detailed exhaust flow analysis with no spike truncation. Analytical methodwithisentropicplanarflowwasused ® to generatethenozzlecontourthroughMATLAB .The developed code produces a number of outputs comprising nozzle wall profile, flow properties along the nozzle wall, thrust coefficient, thrust, as well as amount of nozzle truncation. Results acquired from designcodeandnumericalanalysesarecomparedfor observing differences. The numerical analysis adopted an inviscid model carried out through commercially available and reliable computational fluid dynamics (CFD) software. Use of the developed code would assist the readers to perform quick analysis of different aerodynamic design parameters for the aerospike nozzlethathastremendousscopeof applicationinfuturelaunchvehicles.

—CFX is applied to study of the transonic multicomponent gas field in the adjustable convergent-divergent nozzles of the aero engine. The influences of different flight conditions on the three-dimensional transonic flow fields are analyzed numerically. The accuracy of the k-omega turbulence model is verified through the comparison between the numerical results and experiment data. And this turbulence model is used to predict transonic flows in general convergent-divergent nozzles. Calculations demonstrate that the average Ma number increases and average temperatures decrease gradually at the outlet of nozzle with the increase of flight altitude. It can be found that variation trend of the flow parameters is reasonable in the researched objects. Numerical simulation is a useful method to consider the effect of wall temperature distributions and to analyze the influence of the exhaust temperature on the infrared radiation. Numerical simulation is appropriate for the improvement and the design of aero engine.

30th Joint Propulsion Conference and Exhibit, 1994

Flows through three reference nozzles have been calculated to determine the capabilities and limitations of the widely used Navier-Stokes solver, PARCo The nozzles examined have similar dominant flow characteristics as those considered for supersonic transport programs. Flows from an inverted velocity profile (IVP) nozzle, an underexpanded nozzle, and an ejector nozzle were examined. PARe calculations were obtained with its standard algebraic turbulence model, Thomas, and the two-equation turbulence model, Chien k-£. The Thomas model was run with the default coefficient of mixing set both at 0.09 and a larger value of 0.13 to improve the mixing prediction. Calculations using the default value substantially underpredicted the mixing for all three flows. The calculations obtained with the higher mixing coefficient better predicted mixing in the NP and underexpanded nozzle flows but adversely affected PARC's convergence characteristics for the NP nozzle case. The ejector nozzle case did not converge with the Thomas model and the higher mixing coefficient. The Chien k-E results were in better agreement with the experimental data overall than were those of the Thomas run with the default mixing coefficient, but the default boundary conditions for k and E underestimated the levels of mixing near the nozzle exits. Nomenclature A cross-sectional area in ejector nozzle mixing region A + van Driest damping constant = 26 C EI Chien k-E turbulence model constant = 1.35 C E2 Chien k-E turbulence model constant = 1.8 C Il Chien k-E turbulence model constant = 0.09 fw f l , f2 terms in Chien k-E turbulence model H distance from centerline to top or bottom wall of ejector nozzle K Von Karman constant = 0.41 k turbulent kinetic energy p density CJ k Chien k-£ turbulence model constant = 1.0 CJ E Chien k-£ turbulence model constant = 1.3 w vorticity Wc Thomas model maximum vorticity Subscripts: i, j computational coordinates max maximum min minimum p density CJ k Chien k-£ turbulence model constant = 1.0 CJ E Chien k-£ turbulence model constant = 1.3 w vorticity Wc Thomas model maximum vorticity Subscripts: i, j computational coordinates max maximum min minimum OF REPORT OFTHIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified NSN 7540-01 -280-5500 S tandard Form 2 98 (R ev . 2-89) Prescribed by ANSI Std. Z39-18 298-102

Progress in Aerospace Sciences, 2006

This article presents the current status of computational fluid dynamics (CFD) methods as applied to the simulation of turbulent jet flowfields issuing from aircraft engine exhaust nozzles. For many years, Reynolds-averaged Navier-Stokes (RANS) methods have been used routinely to calculate such flows, including very complex nozzle configurations. RANS methods replace all turbulent fluid dynamic effects with a turbulence model. Such turbulence models have limitations for jets with significant three-dimensionality, compressibility, and high temperature streams. In contrast to the RANS approach, direct numerical simulation (DNS) methods calculate the entire turbulent energy spectrum by resolving all turbulent motion down to the Kolmogorov scale. Although this avoids the limitations associated with turbulence modeling, DNS methods will remain computationally impractical in the foreseeable future for all but the simplest configurations. Large-Eddy simulation (LES) methods, which directly calculate the large-scale turbulent structures and reserve modeling only for the smallest scales, have been pursued in recent years and may offer the best prospects for improving the fidelity of turbulent jet flow simulations. A related approach is the group of hybrid RANS/LES methods, where RANS is used to model the small-scale turbulence in wall boundary layers and LES is utilized in regions dominated by the large-scale jet mixing. The advantages, limitations, and applicability of each approach are discussed and recommendations for further research are presented. r

42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004

Computational Fluid Dynamics (CFD) analyses of axisymmetric circular-arc boattail nozzles operating off-design at transonic Mach numbers have been completed. These computations span the very difficult transonic flight regime with shock-induced separations and strong adverse pressure gradients. External afterbody and internal nozzle pressure distributions computed with the Wind code are compared with experimental data. A range of turbulence models were examined, including the Explicit Algebraic Stress model. Computations have been completed at freestream Mach numbers of 0.9 and 1.2, and nozzle pressure ratios (NPR) of 4 and 6. Calculations completed with variable timestepping (steady-state) did not converge to a true steady-state solution. Calculations obtained using constant timestepping (time-accurate) indicate less variations in flow properties compared with steady-state solutions. This failure to converge to a steady-state solution was the result of using variable time-stepping with large-scale separations present in the flow. Nevertheless, time-averaged boattail surface pressure coefficient and internal nozzle pressures show reasonable agreement with experimental data. The SST turbulence model demonstrates the best overall agreement with experimental data.