Validation of Under-Resolved Numerical Simulations of the PDC Exhaust Flow Based on High Speed Schlieren

Abstract

Owing to their high thermodynamic efficiency, pulsating combustion cycles have become an attractive option for future gas turbine designs. Yet, their potential gains should not be outweighed by losses due to unsteady pressure wave interactions between engine components. Consequently, the geometric engine design moves into focus. Ideally, one would quickly test several different principal layouts with respect to their qualitative behavior, select the most promising variants and then move on to detailed optimization. Computational fluid dynamics (CFD) appears as the methodology of choice for such preparatory testing. Yet, the inevitable geometric complexity of such engines makes fully resolved CFD an arduous and expensive task necessitating computations on top high-performance hardware, even with modern adaptive mesh refinement in place. In the present work we look at the initial flow field of a shock generated by a pulse detonation combustor (PDC) which leaves the combustion chamber and enters the plenum. We provide first indicators, however, that overall mechanical loads, represented by large-scale means of, e.g., mass, energy, and momentum fluxes can be well estimated on the basis of rather coarsely resolved CFD calculations. Comparing high-resolution simulations of the exit of a strong shock from a combustion tube with experimental schlieren photographs, we first

Aeroacoustic resonance and self-excitation in screeching and impinging supersonic jets – A review

“…Consider the series of time-resolved schlieren images of a starting jet produced by a deflagration-detonation-transition presented in Figure 30. 223,224 Here the vortex in question is the starting-vortex, rather than a typical shear layer vortex, and is thus far stronger than those observed in steady jets, which makes the Figure 29. Schematic representation of a vortex interacting with a stationary shock, based on the numerical results of Grasso and Pirozzoli.…”

“…Consider the series of time-resolved schlieren images of a starting jet produced by a deflagration-detonation-transition presented in Figure 30. 223,224 Here the vortex in question is the starting-vortex, rather than a typical shear layer vortex, and is thus far stronger than those observed in steady jets, which makes the phenomenon easier to visualize. The first image (half of which is replaced with a schematic representation), shows a typical triple shock formation characteristic of an underexpanded jet, but with the reflected shock terminating in the leading vortex ring.…”

Investigation of the Exhaust Flow of a Pulse Detonation Combustor at different Operating Conditions based on High-Speed Schlieren and PIV

“…These exhaust and suction phases are caused by a number of compression and expansion waves propagating inside the PDC. These results are very well suited for validation of low-dimensional numerical schemes developed for PDC development [52]. Comparing the PIV results for the partially and overfilled operating condition shows that the fill-fraction only affects the first exhaust phase in respect to the local axial velocity and global volume flux.…”

Diffraction of shock waves through a non-quiescent medium

“…Artificial oscillations at discontinuities in the numerical scheme (such as the shock) are prevented by limiting the slopes of the reconstruction step using the van-Leer limiter (see Toro (2013) for further details). This numerical scheme has been presented in a number of previous works (Nadolski et al 2019;Rezay Haghdoost et al 2020a and is well validated.…”