Numerical Simulation of Steady Supersonic and Hypersonic Flows over Simple Bodies of Revolution. Aero Report 9902

This paper reports on numerical results for supersonic and hypersonic steady flows over axisymmetric blunt bodies. Two-dimensional compressible Navier- Stokes equations are solved using a high- resolution upwind Roe’s scheme. A modification to the boundary conditions and the implementation of Harten’s entropy fix is proposed to improve the robustness of the code, which is then tested on an axisymmetric spike, cone and cylinder at freestream Mach numbers of 2.21, 6.00 and 30.00

Numerical Simulation of High-Speed Unsteady Flows over Axisymmetric Spiked Bodies. Aero Report 9903

The present paper reports some preliminary numerical results for the supersonic/hypersonic unsteady flow over a family of spiked blunt bodies. Axisymmetric compressible Navier-Stokes equations are solved using a high- resolution unfactored implicit upwind Roe’s scheme and a time-accurate pseudo-time method is employed for advancing in time. Unsteady flow arising at Mach 2.21 and Mach 6.00 around the spiked 50°, 70° cone and cylinder are simulated and the computational results are compared with measurements. The study on these simple shapes for which experimental results are available provides a demonstration that such unsteady flows can be predicted reasonably well and provides confidence that more complex flows such as intake ’’buzz” and high Reynolds’ number ablation can be tackled

Numerical investigation of the effect of shock-induced flow separation on dynamic stall in time-varying freestream conditions

Dynamic stall on an oscillatory pitching NACA 0012 airfoil was simulated via CFD under time-varying freestream conditions, which are representative of fast forward flight for a helicopter and which lead to transonic effects at the minimum of the pitch angle. The selected flow conditions were representative of a helicopter blade section at around 80% of the blade radius at the extreme of the forward flight speed, i.e. at around Mach 0.3. A sinusoidal pitch angle variation of 15° ± 10° and an out-of-phase sinusoidal freestream variation of Mach 0.48 ± 0.3 were applied at a mean reduced frequency of 0.029. The mean Reynolds number was approximately 3.3 x 106. First, the simulation results for steady freestream dynamic stall were carefully validated with experiment. Then, the steady and unsteady freestream dynamic stall simulations were compared. Key findings include the lift coefficient hysteresis loop changing direction for the variable freestream conditions, as well as the peak values of lift, drag and negative pitching moment coefficients increasing by factors of approximately 2~4. Results suggest that the mechanism of dynamic stall changes dramatically due to the occurrence of transonic flow at minimum angle of attack and confirms that inclusion of time-varying freestream in dynamic stall simulations is important for the extremes of the forward flight speed