Unsteady characteristics of shock wave in a supersonic diffuser is a major phenomenon influencing starting of a wind tunnel or a high speed intake. Many researchers attempted to study this phenomenon using acoustic aspects, spatial excursion of the shock and shock wave boundary layer interactions (SBLI). In this study, the effect of Mach number variation on shock oscillations across a second throat of a supersonic diffuser is investigated. The effect of hydraulic diameter of the test section is also carried out.
The experimental facility is a 2-D rectangular blowdown supersonic wind tunnel. The facility is designed in a modular way, where in the nozzle, test section and diffuser are made in one block of metal. The blocks are fabricated for the regime of Mach numbers varying from 1.6 to 3.2. These blocks are changed to study the effect of Mach number on shock oscillations across second throat and also the effect of hydraulic diameter. High speed schlieren imaging is employed to visualise the flow. Stagnation pressure in settling chamber and unsteady pressures on the diffuser blocks near second throat (both upstream and downstream) were also monitored. The schematic of the facility is shown in Fig. 1.
The stagnation pressure is kept constant in each run of the experiments. The time variation of shock location and pressure downstream of second throat are analyzed. The schematic of time variation of the shock location is shown in Fig. 2a. Xs = 0 represents the second throat location. It is evident that shock oscillates across the second throat. From the histogram of the shock location, shown in Fig. 2b, it is observed that shock oscillates across second throat and does not stay at second throat. Schlieren images of the shock across the second throat is shown in Fig. 3. The images show the unsteadiness of the shock. From the tests carried out, it is found that the normal shock wave oscillations across the throat occur upto Mach 2.2 and with further increase in Mach number, transition from mach to regular reflection takes place and the normal shock in the center line disappears.
The full paper will contain the effect of Mach number variation on dynamics of shock oscillations, time variation of shock location, Fourier space analysis of unsteady pressure measurements for various Mach numbers.
References:
- J.K. Bruce, H. Babinsky (2008) " An experimental study of transonic shock/boundary layer interactions subject to downstream pressure perturbations " Aerospace science and Technology, Vol. 14, Issue 2, pp-134-142.
- Bogar, T.J., Sajben, M. and Kroutil, J.C.(1983), " Characteristic frequencies of transonic diffuser flow oscillations", AIAA, Vol 21:pp 1232-1240.
- Matsuo,K, Kim,H.D., (1992), "Normal shock wave oscillations in supersonic diffusers", Journal of Shock Waves, Vol 3, pp25-33.
- Jintu K James, Muruganandam T M, "Dynamics of shock oscillation across second throat of a supersonic diffuser under geometry variation", Proceedings of the 2014 International Conference on Mechanics, Fluid Mechanics, Heat and Mass Transfer.
