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Shock Wave and Vortex Interference with the Body Surface

#3872


Comprehensive Study of Shock Wave Interference with a Turbulent Boundary Layer, High-Enthalpy Layer, and Vortex Structure

Tech Area / Field

  • SAT-AER/Aeronautics/Space, Aircraft and Surface Transportation

Status
8 Project completed

Registration date
19.05.2008

Completion date
28.03.2013

Senior Project Manager
Ryzhova T B

Leading Institute
Central Aerodynamic Institute, Russia, Moscow reg., Zhukovsky

Supporting institutes

  • Siberian Branch of RAS / Institute of Theoretical and Applied Mechanics (ITPMech), Russia, Novosibirsk reg., Novosibirsk

Collaborators

  • ONERA, France, Chatillon\nRheinisch-Westfalische Technische Hochschule / Stoßwellenlabor, Germany, Aachen\nUniversité Libre de Bruxelles / Faculté des Sciences Appliquees, Belgium, Brussels

Project summary

The objective of activities is a comprehensive experimental and theoretical (numerical) study of gas flows in regions of shock wave and vortex interference with the body surface. The study of interference zones is of great interest for two reasons. First, interference zones are critical regions of the surface of flying vehicles, because these are zones with intense heating of the surface and a manifold increase in pressure. Second, despite significant achievements of computer technologies and computational methods, it is still impossible to get reliable computations in interference zones, as it could be done for other parts of the flying body. Particularly large difficulties are encountered in calculating turbulent interference flows. Experimental investigations still remain the only means for obtaining principally new information in this field of knowledge.

Shock wave/boundary layer interaction is one of the most urgent problems of today’s aerodynamics. Intense research in this field has been performed for almost 60 years. Some fundamental features of interference flows have been identified. A large volume of quantitative information has been obtained, and the dependence of the maximum pressure and heat-transfer coefficient on free-stream parameters and shock-wave intensity has been found. Research of interference flows has been substantially intensified for the last two decades. Much attention is paid to three-dimensional flows in the vicinity of an isolated wedge or a pair of wedges generating intersecting shock waves, which is typical of the inlet entrance. The main challenge here is the development of adequate methods of numerical simulations of interference flows. Various approaches and various turbulence models are used for turbulent flow calculations. Significant progress has been achieved by using advanced computational capabilities. Nevertheless, the distributions of heat transfer and friction in developed separation zones formed by strong shock waves impinging onto the body surface cannot be yet calculated with acceptable accuracy. It was recognized that the amount of experimental data has to be substantially increased to solve this problem.

Almost all activities aimed at studying interference flows deal with shock-wave interaction with the boundary layer on a flat plate with a sharp leading edge (or a sharp cone). The effect of small-radius bluntness of the body on the gas flow and heat transfer in the interference zone was ignored. At the same time, the leading edges of the flying body are bound to have certain bluntness. It is necessary to reduce the heat flux from the gas onto the leading edge and to restrict the maximum temperature. On the other hand, the radius of bluntness of the leading edges has also to be restricted to avoid an increase in drag.

The influence of small-radius bluntness on the flow past a flat plate or a cone in the absence of any incident shock waves was carefully studied in the 1950-1960s. It was demonstrated that the high-entropy layer generated by bluntness exerts a large effect on the distributions of pressure and heat-transfer coefficients on the plate (or cone) surface even at a large distance from the leading edge (or cone tip). Criteria of similarity determining the influence of small-radius bluntness on the pressure and heat-flux distributions were established. The influence of small-radius bluntness on the flow in the interference zone, however, was first studied only recently by participants of the presently planned project. Some gas-dynamic effects were found, which could facilitate solving the thermal problem of the hypersonic inlet without significant deterioration of its aerodynamic performance. The effects observed were explained on the basis of considering the high-entropy layer characteristics; the influence of the Mach number on the threshold value of bluntness and the maximum heat-transfer coefficient in the interference zone was estimated.

In the works performed, the undisturbed boundary layer was in the laminar state, and the laminar-turbulent transition occurred only inside the separation zone generated by the incident shock wave. At the same time, of the greatest practical interest is the influence of bluntness on interference between the shock wave and the turbulent boundary layer. We can assume that plate bluntness will reduce the heat inflow in the interference region in the turbulent flow as well. Probably, there is also a certain threshold value of bluntness above which the heat transfer is not attenuated and only additional losses of pressure are ensured. The planned study has to provide an answer to this question, as applied to two-dimensional and three-dimensional flows. Obviously, the transition of the boundary layer to the turbulent state ahead of the interference zone will also affect the quantitative characteristics that describe the influence of bluntness on the gas flow and heat transfer in the interference zone.

The project implies experimental investigations of the flow in the zone of incidence of an oblique shock wave at Mach numbers M=6 and 8 in a wide range of Reynolds numbers (up to 25 million, based on the model length), predominantly with a turbulent boundary layer. These experiments will be performed in short-duration wind tunnels of TsAGI and ITAM SB RAS, which provide high flow parameters in moderate-cost experiments. Various methods of research will be used: both conventional methods and new techniques developed by the project participants. The experimental studies will be supported by numerical simulations of the flow within the framework of the Reynolds equations, which will give additional information on the flow and elucidate the capabilities and constraints of numerical codes used.

Another important problem is the streamwise vortex/shock wave interaction. Interference of the vortex with shock waves often leads to vortex breakdown, which, in turn, can deteriorate the lifting capacity of aerodynamic surfaces, lead to inadequate regimes of engine operation and to a drastic increase in heat transfer. Despite the adverse features of this phenomenon, it can be used as one method for improving mixing in the combustor. Therefore, it is also planned to study this type of interaction within the framework of the present project.

One specific feature of interaction of a vortex wake with a shock wave is the unsteadiness of this process. There is an obvious lack of experimental data for quantitative estimates of unsteadiness. The absence of numerical and experimental data for hypersonic velocities should be particularly noted. Preliminary results of experiments performed in T-313 and T-326 wind tunnels based at ITAM SB RAS by the project participants at M=6 demonstrated qualitative and quantitative differences of hypersonic interaction from data for supersonic velocities obtained for M=2-4. The project participants also found that the streamwise vortex can qualitatively change heat transfer on the surface of a blunted body at M=3. This effect can be logically expected to become stronger at hypersonic velocities.

The project proposed includes the study of hypersonic interaction of a streamwise vortex with normal and oblique shocks and obtaining systematic data for Mach numbers M=6 and 8 on the influence of the angle of attack of the vortex generator, vortex strength, and slope of the shock wave on the interaction process. It is also planned to study the effect of vortex strength and the shape of the forebody interacting with the vortex on heat-transfer characteristics. Special attention will be paid to unsteady effects during the interaction process.

The project is intended to help in understanding specific features of shock-wave interaction with a turbulent boundary layer on a slightly blunted body. Information will be obtained on the possibility of reducing heating of the body surface in the region of shock-wave incidence and on the rational size of bluntness with allowance for the influence on heat transfer and on pressure losses caused by formation of an entropy layer. New experimental data will be obtained on a supersonic streamwise vortex, its structure, its interaction with the shock wave, specific features of interaction at hypersonic velocities, vortex breakdown phenomenon, and its effect on body heating.

A database of new experimental results will be obtained, including information on pressure, heat-transfer coefficient, and structure of interference flows. It can be used for verification of numerical codes designed for computing the turbulent flow around various bodies under complicated conditions: incident shock waves, entropy layer, and vortices.

The project proposed is consistent with ISTC goals. It will allow former weapon scientists from TsAGI and ITAM to conduct basic research in peaceful areas, for instance, in creating cost-efficient means for launching payloads to the near-Earth orbit with the use of an air-breathing engine. Close collaboration between TsAGI and ITAM scientists and European partners will be reached.

At all stages, the project will be performed in close cooperation with foreign collaborators, who will participate in the development and approval of the test program, choosing models and methods of research, discussing the results obtained, and preparing joint publications and presentations for international conferences and workshops.

Advanced methods and means of aerodynamic experiments, including panoramic measurement methods, will be used to fulfill the tasks of the project.


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