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Tandem Dual Sonic Jet Injection into a Supersonic Cross-Flow

Authors: J.S. Smink, E.T.A. van der Weide, H.W.M. Hoeijmakers, and C.H. Venner
(Thermal and Fluid Engineering department, University of Twente, The Netherlands)

Two sonic jets in tandem configuration, injected into a Mach 1.6 supersonic cross-flow. The jets should penetrate into the cross-flow in order to mix with the cross-flow. Schlieren snapshots from wind tunnel experiments are complemented by numerical time-resolved Delayed Detached Eddy Simulation (DDES) to obtain insight into the detailed flow phenomena [3]. (J = 3.8, S = 7.17)

Scientific Abstract:

At high speeds, supersonic combustion ramjets (scramjets) are used. In these jet engines, the high-Mach-number supersonic incoming flow is decelerated to a lower supersonic Mach number, in which the fuel is injected. Before ignition, the fuel penetrating into this cross-flow needs to efficiently mix with the incoming air. Jet injection into a supersonic cross-flow is a model problem for such fuel injection. Due to shock waves that arise, total pressure is lost, which results in a loss of efficiency. Therefore, it is desired to have a deep penetration, but with a minimum of losses.

A method to increase jet penetration with low total pressure losses is using two sonic jets in tandem configuration, in which the upstream jet induces a bow shock that slows down the flow, such that the main, downstream, jet penetrates further into the crossflow. The two governing parameters are the jet-to-cross-flow momentum flux ratio J (the relative strength of the jet compared to the crossflow) and S the dimensionless distance between the two jets. The study has shown that for given J, there is an optimal value of S for which jet penetration is maximal [1].

In the experimental work, side-view Schlieren images have been obtained, at a frame rate limited to 1 kfps. To obtain more insight, numerical simulations have been performed based on Delayed Detached Eddy Simulations (DDES), which enables accessing the top view and the exit plane (viewed in upstream direction) in detail [3]. The used time resolution is 2 Mfps, so that flow features with characteristic time scales down to 1 μs are captured. The condition chosen is J = 3.8 for which S = 7.17 is close to the optimum distance of the jet. The mesh resolution is 434,191,045 grid points.

The combination of experimental and numerical results reveals that the time-resolved results are indispensable for determining the time-averaged properties, such as the penetration depth of the injection in the cross-flow. The interacting vortical structures in the jet plume, as viewed from the side and in the exit-plane show that the jet with vortex-dipole cross-section enhances mixing of the jet with the cross-flow. Furthermore, the simulations show that the jets interact with the bow shocks, resulting in oscillatory behavior of the bow shocks, which was also observed in the Schlieren snapshots from experiments.

List of recent publications

[1] J.S. Smink, S. de Maag, C.W. Lerink, E. Giskes, H.W.M. Hoeijmakers, C.H. Venner, F.B. Segerink, and H.L. Offerhaus. “Schlieren Visualization of Dual Injection in Supersonic Cross Flow”. In: HiSST: 2nd International Conference on High-Speed Vehicle Science Technology, Bruges, Belgium (2022). Best Overall Paper Award.

[2] J.S. Smink, H.W.M. Hoeijmakers, and C.H. Venner. “Dual Injection in Supersonic Crossflow: Analysis Jet Shear Layer from Schlieren Images.” AIAA Journal 60(11) (2022), pp. 62776288.

[3] S. de Maag, J.S. Smink, E.T.A. van der Weide, H.W.M. Hoeijmakers, and C.H. Venner. “Numerical/Experimental Study Dual Injection in Supersonic Cross Flow”. In: HiSST: 3rd International Conference on High-Speed Vehicle Science Technology, Busan, Republic of Korea (2024). Best Student Paper Award.