Tomographic visualization of the Hypersonic Flow Field over a Waverider

Abstract

Waveriders are geometric configurations proposed for hypersonic flight, which benefit from the lift generated by the shock wave [1]. They are designed not only to achieve high lift to drag ratios but also forebody shock compression which is essential for the intakes of hypersonic propulsion systems. Typically a conically derived waverider has its upper surface parallel to the freestream offering no obstruction to the flow, while the lower surface obstructs the flow and results in a shock, resulting in the required lift production. The lower surface is tailored in such a way that the shock is attached to the edges so as to avoid spillage from the bottom to top surfaces. Detailed shock tunnel studies have been initiated in Laboratory for Hypersonic and Shockwave Research, Department of Aerospace Engineering, IISc, Bangalore, on understanding the flow field over waverider configurations. A waverider configuration for the present study designed for Mach 6 flow conditions (to be placed at 2.5⁰ incidence to the freestream) is shown in Fig. 1 [2]. Table 1 shows the freestream conditions for the present study simulated in the IISc hypersonic shock tunnel HST-2 [3,4].

It can be directly inferred by looking at the geometry that the flow field over a wave rider is naturally 3-dimensional. Conventional high speed visualizations like schlieren provide information which is integrated over the entire span of the flow, and hence qualitatively present a 2-dimensional picture of the flow field. While for nearly 2-dimensional flows over large spans or for axisymmetric flows (due to similarity in all azimuthal planes), such visualizations provide reliable information. However, for 3-dimensional configurations the schlieren visualizations are deceptive. A schlieren visualization in HST-2 of the wave rider in the mentioned freestream conditions is shown in Fig. 2, obtained with the plane of symmetry of waverider placed perpendicular to the parallel beam. It is clearly an oversimplified picture of the flow field, where it is difficult to differentiate it from the flow field over a 2-dimensional wedge, except that the angle of the shock is lesser than what may be expected from oblique shock theory for the apparent wedge angle in the shadow 12.4º. Thus it is desirable that the flow field is visualized over various planes, by rotating the wave rider model about the mounting axis; from the different images corresponding to different planes of the shadow, the three dimensional picture can be inferred. Two techniques shall be employed in the proposed lines. The different azimuthal planes of the flow can be viewed using conventional schlieren technique, and from the apparent shock shapes for each plane, a qualitative 3-dimensional picture may be obtained. The other technique that shall be employed is the quantitative shadow casting technique proposed by Medhi et al. (2011) [5]. While the tomographic technique was applied for axisymmetric body, in the present study, through the visualization of various azimuthal planes, the technique shall be extended for the 3-dimensional configuration. The results of the visualization studies shall be detailed in the full paper.

Figure 1: A photograph of the waverider model.

Figure 2: A schlieren image of Mach 6 flow over waverider.

Table 1. Free stream conditions in HST2.

References:

1. Townend, L., H., “Research and Design for Lifting Re-entry”, Progress in Aerospace Sciences, Vol.18, Pergamon Press, London, 1979.
2. Hemanth, Kolla., “Force Measurements on Conically Derived Mach 6 Hypersonic Waverider ”,M.E, Thesis, IISc, 2005.
3. Jagadeesh, G., “Experimental Investigations of the Flow Fields around Large Angle Blunt Cones Flying at Hypersonic Mach Number”, PhD Thesis, Aerospace Engg., Indian Institute of Science, Bangalore, India, 1997.
4. Nagashetty, R. Sriram, S. Saravanan, G. Jagadeesh and K. P. J. Reddy, "Heat Transfer Measurements On Waverider at Hypersonic Mach Numbers" 19th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, AVIATION 2014, Atlanta, USA, 16-20, June, 2014 (AIAA2014_2507).
5. Biswajit Medhi, G.M. Hegde, K.P.J. Reddy, D. Roy, and R.M. Vasu, “Quantitative visualization of high speed flow through optical tomography” 28^th International Symposium on Shock Waves (ISSW28), Manchester, 17-22, July, 2011.