18th AIAA/3AF International Space Planes and Hypersonic Systems and Technologies Conference, 2012
A numerical analysis of a three-dimensional intake model used during an experimental test campaig... more A numerical analysis of a three-dimensional intake model used during an experimental test campaign under Mach 8 flight conditions is presented. A passive bleed has been used during the experimental tests and is numerically investigated here. The influence of the suction gap on the inhomogeneous flow in the interior intake is studied with respect to its effect on the strut injection system. The computations are performed with the in-house scientific research code QUADFLOW.
The simulation of hypersonic flows is computationally demanding due to the large gradients of the... more The simulation of hypersonic flows is computationally demanding due to the large gradients of the flow variables at hand, caused both by strong shock waves and thick boundary or shear layers. The resolution of those gradients imposes the use of extremely small cells in the respective regions. Taking turbulence into account intensifies the variation in scales even more. Furthermore, hypersonic flows have been shown to be extremely grid sensitive. For the simulation of fully three-dimensional configurations of engineering applications, this results in a huge amount of cells and as a consequence prohibitive computational time. Therefore, modern adaptive techniques can provide a gain with respect to both computational costs and accuracy, allowing the generation of locally highly resolved flow regions where they are needed and retaining an otherwise smooth distribution. In this paper, an h-adaptive technique based on wavelets is employed for the solution of hypersonic flows. The compressible Reynolds averaged Navier-Stokes equations are solved using a differential Reynolds stress turbulence model, well suited to predict shock-wave-boundary-layer interactions in high enthalpy flows. Two test cases are considered: a compression corner at 15 degrees and a scramjet intake. The compression corner is a classical test case in hypersonic flow investigations because it poses a shock-wave-turbulent-boundary-layer interaction problem. The adaptive procedure is applied to a two-dimensional configuration as validation. The scramjet intake is firstly computed in two dimensions. Subsequently a three-dimensional geometry is considered. Both test cases are validated with experimental data and compared to non-adaptive computations. The results show that the use of an adaptive technique for hypersonic turbulent flows at high enthalpy conditions can strongly improve the performance in terms of memory and CPU time while at the same time maintaining the required accuracy of the results. Nomenclature cp : Specific heat at constant pressure, pressure coefficient [-] δij : Kronecker Delta [-] E : Specific total energy [m 2 /s 2 ] : Turbulence dissipation rate [m 2 /s 3 ] ε : Threshold value used for data compression [-] ε l : Level-dependent threshold value for level l [-] H : Total specific enthalpy [m 2 /s 2 ] k : Turbulent kinetic energy [m 2 /s 2 ] II : Second invariant of the anisotropy tensor [-] L : Maximal refinement level [-] l : Local refinement level [-] µ : Molecular viscosity [kg/(m s)] ω : Specific turbulence dissipation rate [1/s] p : Pressure [Pa] pt : Total pressure [Pa] qi : Component of heat flux vector [W/m 2 ] q (t) k : Turbulent heat flux [W/m 2 ] ρ : Density [kg/m 3 ] St : Stanton number [-] t : Time [s] T : Temperature [K] Tw : Wall temperature [K] T0 : Total temperature [K] U : Local velocity [m/s] ui : Velocity component [m/s] xi : Cartesian coordinates component [m] x, y, z : Cartesian coordinates [m] y + : Dimensionless wall distance [-] M : Mach number [-] Re : Reynolds number [1/m] bij : Anisotropy tensor [-] Dij : Diffusion tensor for the Reynolds stresses [m 2 /s 3 ] ij : Destruction tensor for the Reynolds stresses [m 2 /s 3 ] Mij : Turbulent mass flux tensor for the Reynolds stresses [m 2 /s 3 ] Πij : Re-distribution tensor for the Reynolds stresses [m 2 /s 3 ] Pij : Production tensor for the Reynolds stresses [m 2 /s 3 ] Sij : Strain rate tensor [1/s] Rij : Reynolds stress tensor [m 2 /s 2 ] τij : Viscous stress tensor [m 2 /s 2 ] Wij : Rotation tensor [1/s] ∂· ∂· : Partial derivative · : Reynolds-averaged quantitỹ · : Favre-averaged quantity ·∞ : Free stream value
... Turbulence closure is achieved using two eddy-viscosity models and a differential Reynolds-st... more ... Turbulence closure is achieved using two eddy-viscosity models and a differential Reynolds-stress model. ... (6) The turbulent diffusion (¯ρDkk) in Eqn. 3 is modeled based on simple gradient diffusion hy-pothesis for eddy-viscosity models [16]: ¯ρDkk = ∂ ∂xk ...
This paper shall present the numerical results of an investigation into the effect of wall to fre... more This paper shall present the numerical results of an investigation into the effect of wall to freestream temperature on boundary layer separation for a nominal flat plate/ 15degree compression corner. The numerical results will be compared to the experimental results of Bleilebens and Olivier (1). The major findings from their study showed a distinct trend for boundary layer separation size to increase with wall-to-freestream temperature ratio; that the separation process was dictated purely by laminar effects; and that the separated shear layer transitioned to turbulence during the reattachment process. The transitional behaviour of the reattaching shear layer was characterised in their results through high Stanton number distributions post-reattachment and the observance of Gortler vortices in the infrared thermography images. Reinartz et al (2) focussed upon assessment of the role of wall temperature and en- tropy layer effects for double wedge configurations, but featured an initial numerical study into the flat plate/ compression corner of Bleilebens and Olivier upon which this paper is founded. The present investigation shall build and expand upon these initial calculations. The compression corner calculations showed agreement with the separation size growth encountered during the Bleilebens and Olivier (1) experiment with increasing wall-to- freestream temperature ratio. Although the results from the FLOWer CFD code agreed well for separation size, the pressure level over the separation bubble was found to be considerably higher than that found experimentally. The 2D laminar simulations calcu- lated with the CFD++ code overpredicted the experimental separation and the pressure level within the separation bubble, however. The expansion process post reattachment was also found to be under-predicted for both CFD codes used; these discrepancies were attributed to 3D effects neglected within the simulations. Significant improvement in the 2D double-wedge simulations were found when a turbulence model was applied at the hinge line between the first and second ramps. A schematic (from Bleilebens and Olivier (1)) of the typical flow is given in Figure 1. The figure depicts the recirculation zone produced by the separated boundary layer; the separation and reattachment shocks; the 'triple point' where these shocks intersect and the expansion fan issuing from this intersection that is necessary for matching the pressure between streamlines that pass through the separation and reattachment shocks and streamlines that pass through the main ramp shock.
18th AIAA/3AF International Space Planes and Hypersonic Systems and Technologies Conference, 2012
A numerical analysis of a three-dimensional intake model used during an experimental test campaig... more A numerical analysis of a three-dimensional intake model used during an experimental test campaign under Mach 8 flight conditions is presented. A passive bleed has been used during the experimental tests and is numerically investigated here. The influence of the suction gap on the inhomogeneous flow in the interior intake is studied with respect to its effect on the strut injection system. The computations are performed with the in-house scientific research code QUADFLOW.
The simulation of hypersonic flows is computationally demanding due to the large gradients of the... more The simulation of hypersonic flows is computationally demanding due to the large gradients of the flow variables at hand, caused both by strong shock waves and thick boundary or shear layers. The resolution of those gradients imposes the use of extremely small cells in the respective regions. Taking turbulence into account intensifies the variation in scales even more. Furthermore, hypersonic flows have been shown to be extremely grid sensitive. For the simulation of fully three-dimensional configurations of engineering applications, this results in a huge amount of cells and as a consequence prohibitive computational time. Therefore, modern adaptive techniques can provide a gain with respect to both computational costs and accuracy, allowing the generation of locally highly resolved flow regions where they are needed and retaining an otherwise smooth distribution. In this paper, an h-adaptive technique based on wavelets is employed for the solution of hypersonic flows. The compressible Reynolds averaged Navier-Stokes equations are solved using a differential Reynolds stress turbulence model, well suited to predict shock-wave-boundary-layer interactions in high enthalpy flows. Two test cases are considered: a compression corner at 15 degrees and a scramjet intake. The compression corner is a classical test case in hypersonic flow investigations because it poses a shock-wave-turbulent-boundary-layer interaction problem. The adaptive procedure is applied to a two-dimensional configuration as validation. The scramjet intake is firstly computed in two dimensions. Subsequently a three-dimensional geometry is considered. Both test cases are validated with experimental data and compared to non-adaptive computations. The results show that the use of an adaptive technique for hypersonic turbulent flows at high enthalpy conditions can strongly improve the performance in terms of memory and CPU time while at the same time maintaining the required accuracy of the results. Nomenclature cp : Specific heat at constant pressure, pressure coefficient [-] δij : Kronecker Delta [-] E : Specific total energy [m 2 /s 2 ] : Turbulence dissipation rate [m 2 /s 3 ] ε : Threshold value used for data compression [-] ε l : Level-dependent threshold value for level l [-] H : Total specific enthalpy [m 2 /s 2 ] k : Turbulent kinetic energy [m 2 /s 2 ] II : Second invariant of the anisotropy tensor [-] L : Maximal refinement level [-] l : Local refinement level [-] µ : Molecular viscosity [kg/(m s)] ω : Specific turbulence dissipation rate [1/s] p : Pressure [Pa] pt : Total pressure [Pa] qi : Component of heat flux vector [W/m 2 ] q (t) k : Turbulent heat flux [W/m 2 ] ρ : Density [kg/m 3 ] St : Stanton number [-] t : Time [s] T : Temperature [K] Tw : Wall temperature [K] T0 : Total temperature [K] U : Local velocity [m/s] ui : Velocity component [m/s] xi : Cartesian coordinates component [m] x, y, z : Cartesian coordinates [m] y + : Dimensionless wall distance [-] M : Mach number [-] Re : Reynolds number [1/m] bij : Anisotropy tensor [-] Dij : Diffusion tensor for the Reynolds stresses [m 2 /s 3 ] ij : Destruction tensor for the Reynolds stresses [m 2 /s 3 ] Mij : Turbulent mass flux tensor for the Reynolds stresses [m 2 /s 3 ] Πij : Re-distribution tensor for the Reynolds stresses [m 2 /s 3 ] Pij : Production tensor for the Reynolds stresses [m 2 /s 3 ] Sij : Strain rate tensor [1/s] Rij : Reynolds stress tensor [m 2 /s 2 ] τij : Viscous stress tensor [m 2 /s 2 ] Wij : Rotation tensor [1/s] ∂· ∂· : Partial derivative · : Reynolds-averaged quantitỹ · : Favre-averaged quantity ·∞ : Free stream value
... Turbulence closure is achieved using two eddy-viscosity models and a differential Reynolds-st... more ... Turbulence closure is achieved using two eddy-viscosity models and a differential Reynolds-stress model. ... (6) The turbulent diffusion (¯ρDkk) in Eqn. 3 is modeled based on simple gradient diffusion hy-pothesis for eddy-viscosity models [16]: ¯ρDkk = ∂ ∂xk ...
This paper shall present the numerical results of an investigation into the effect of wall to fre... more This paper shall present the numerical results of an investigation into the effect of wall to freestream temperature on boundary layer separation for a nominal flat plate/ 15degree compression corner. The numerical results will be compared to the experimental results of Bleilebens and Olivier (1). The major findings from their study showed a distinct trend for boundary layer separation size to increase with wall-to-freestream temperature ratio; that the separation process was dictated purely by laminar effects; and that the separated shear layer transitioned to turbulence during the reattachment process. The transitional behaviour of the reattaching shear layer was characterised in their results through high Stanton number distributions post-reattachment and the observance of Gortler vortices in the infrared thermography images. Reinartz et al (2) focussed upon assessment of the role of wall temperature and en- tropy layer effects for double wedge configurations, but featured an initial numerical study into the flat plate/ compression corner of Bleilebens and Olivier upon which this paper is founded. The present investigation shall build and expand upon these initial calculations. The compression corner calculations showed agreement with the separation size growth encountered during the Bleilebens and Olivier (1) experiment with increasing wall-to- freestream temperature ratio. Although the results from the FLOWer CFD code agreed well for separation size, the pressure level over the separation bubble was found to be considerably higher than that found experimentally. The 2D laminar simulations calcu- lated with the CFD++ code overpredicted the experimental separation and the pressure level within the separation bubble, however. The expansion process post reattachment was also found to be under-predicted for both CFD codes used; these discrepancies were attributed to 3D effects neglected within the simulations. Significant improvement in the 2D double-wedge simulations were found when a turbulence model was applied at the hinge line between the first and second ramps. A schematic (from Bleilebens and Olivier (1)) of the typical flow is given in Figure 1. The figure depicts the recirculation zone produced by the separated boundary layer; the separation and reattachment shocks; the 'triple point' where these shocks intersect and the expansion fan issuing from this intersection that is necessary for matching the pressure between streamlines that pass through the separation and reattachment shocks and streamlines that pass through the main ramp shock.
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Papers by B. Reinartz