Unsteady Performance of Rotating Detonation Engines with Different Exhaust Nozzles

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Unsteady Performance of Rotating Detonation Engines with Different Exhaust Nozzles

Braun, James

In this paper, OpenFoam, an open source unsteady Reynolds-averaged Navier–Stokes software was carefully examined to analyze rotating detonation combustors. This tool was subsequently used to quantify the effect of the outlet conditions on five different exhaust nozzle geometries. Both detonation and deflagration of the hydrogen–air mixture were taken into account in the source terms of the species transport equation. The premixed H2–air mixture was injected at three different total pressures, ranging from 0.4 to 0.8 MPa. First, the rotating detonation combustor was described, and then five different nozzles were investigated: straight duct, conical, Bezier outer wall, Bezier inner wall, and two Bezier surfaces. All the nozzles were compared regarding their outlet total temperature, pressure gain, exit Mach number, and outlet flow angle. The use of a straight duct nozzle generated a noticeable drop in pressure gain of about 27% compared to the baseline combustor. The conical nozzle expanded the combustor outlet flow from sonic conditions into Mach 1.8 to 2.3. The Bezier outer wall underperformed compared to the conical nozzle at low combustor inlet pressures, while the situation was reversed at higher combustor inlet pressures. Using the inner wall as a divergent section showed no benefits in terms of Mach number and total pressure. The use of a nozzle with two Bezier surfaces did not provide any significant benefits in spite of the enhanced outlet-to-combustor-inlet-area ratio.