INTRODUCTION
It is a well-known fact that hypersonic wind tunnels cannot reproduce turbulent boundary layer on smooth model surface. This is a generic problem which has a negative impact on the prediction of stability characteristic for any high velocity project development. To overcome the problem it is necessary to artificially induce the boundary layer to a turbulent state by means of surface roughness on the nose of the model at special positions. Computational fluid dynamics (1-3) must play a major role in the development of hypersonic vehicles (Figure 1 left) because ground test facilities, including the IAI hypersonic wind tunnel, are not able to fully simulate flight conditions. Numerically RANS computed trip database (Figure 1 center) relying on an interface program to extract boundary layer edge properties and on existing transition criteria have been used to produce charts of the effective perturbation height taking into account the Reynolds and Mach numbers (Figure 1 right), as well as the bluntness ratio variations.
The goal of the current work is to assess the impact of the trips (size, shape, distribution) on the length of the shock-boundary-layer interaction at separation and reattachment region for two blunt-cones-flare with two different flare angles (20 and 37 degrees) and two ratios of the nose / base radii (15% and 20%). The trips were manufactured using direct metal laser sintering technology well suited for rapid prototyping at low cost (Figure 2 right). The mechanical design and production (Figure 2 center up) of the hypersonic wind-tunnel blunt cone flare models was done at IAI. Enhancement of the Schlieren diagnostic visualization techniques in use at IAI is also addressed introducing the monochromatic laser used for shock-tube experiment at BGU laboratory as a new monochromatic light source. Results for a first batch of hypersonic wind tunnel experiments with preliminary analysis are also presented. The reader is referred to previous publications concerning previous work on simple blunt cone without flare (4). Quantitative data collected during the experiments are forces and moments and static pressure at the cone flare corner. Qualitative information will be gathered via the use of a focused laser Schlieren to permit a close-up view of the shocks and boundary-layers at the corner junction between the cone and the flare and thus to characterize the state of the boundary-layer between laminar and turbulent with and without trips.
RESULTS
Smooth and tripped blunt cone flares numerical simulations of the shock turbulent boundary layer interaction at the cone flare junction have been done using the latest hypersonic multigrid version of the IAI in-house multiblock parallel reactive NES code (1-3) that permits to speed-up the convergence to steady state by a factor of 5 compared to the grid sequencing solver. A first trip transition correlation is reached for the IAI hypersonic wind-tunnel.
CONCLUSIONS
This R&D on hypersonic forced transition is crucial for reliable hypersonic wind tunnel tests and is a central design element for high velocity projects like for innovative scramjet propulsion based platforms.
Figure 1: NES Hypersonic Multigrid CFD – Left : Hypersonic Glider with Real Gas Effects – Center & Right: IAI HYWT first Trip correlation based on massive parallel HPC
Figure 2: Left: Schlieren visualization – Right: Trip Hardware of Cone
References
1. Séror, S.,”Two Major Steps Towards a Multigrid Hypersonic Real Gas Version of the Industrial Code NES for Accurate Heat-Transfer Predictions of High Speed Vehicles”, Proceedings of the 54th Israel Annual Conference on Aerospace Sciences, Tel-Aviv, (February 2014).
2. Seror, S., Hefets, J., "Extension and Validation of NES vs. IAI Blow-Down Cold Hypersonic Wind-Tunnel including High Angle of Attack Hypersonic Generic Missile CFD Prediction", STAI / AEDC Conference Nashville USA (April 2008).
3. Seror, S., Rubin, T., Peigin, S., and Epstein, B., "Development of an Accurate Multiblock Multiface Parallel 3D ENO driven Multigrid Cycling Navier-Stokes Code NES with the Spalart-Allmaras Model for Complex Aerodynamic Configurations", Proceedings of the West East High Speed Flow Fields Conference, Marseilles, CIMNE Eds, (April 2002).
4. Wexler, J, Seror, S, Hefetz, J, Sadot, O, Ram, O, "Design of a First Hypersonic Wind-Tunnel Experiment of a Variable Blunt Cone with Trips to Induce Boundary Layer Transition to Turbulence Including Development of a Laser Based Optical Schlieren Method to Visualize the Boundary Layer Transition to Turbulence", Proceedings of the 53rd Israel Annual Conference on Aerospace Sciences, Tel-Aviv, (March 2013).
