Effect of Low Pressure Ratio on Exhaust Plumes of Rotating Detonation Engines

Abstract

Rotating Detonation Engines (RDEs) operating at low injection pressure compared to back pressure are attractive for air breathing engines due to the possibility to greatly simplify the compressor design.Typical RDE simulations that use a mixed subsonic/supersonic boundary at the exhaust plane may not provide an accurate description of the flow field within the expansion region of the combustion chamber. Previous simulations at high pressure showed that the addition of an exhaust plenum causes only minimal changes in the RDE flow field, most significantly at the exhaust plane. The current work examines the flow field and exhaust flow characteristics for low pressure RDEs and include both three-dimensionality effects and the effects of an exhaust plenum. Including three-dimensional effects resulted in a lower detonation wave velocity at low pressure ratios due to detonation wave failure at the inner wall, which was not captured in the twodimensional simulations. While the inclusion of an exhaust plenum to the solution did not change the basic shock wave structure that is set up in the low pressure ratio RDE, the specific strengths and location of the shock waves were different, and resulted in a lower pressure in the fill region of the RDE and thus a lower thermodynamic efficiency. The specific impulse varied by as much as 12.7% between the 2D and 3D results with an exhaust plenum for a pressure ratio of 2.5. Nomenclature a = ratio of micro-injector throat area to injection face area, non-dimensional = specific heat at constant pressure for species k, ergs/(gm K) = specific heat at constant volume for species k, ergs/(gm K) = total energy, ergs/cm 3 = pressure, dynes/cm 2 = mixture ideal gas constant, ergs/(gm K) = ideal gas constant for species k, ergs/(gm K) = temperature, K = induction time, s = velocity of gas, cm/s = reaction rate for reactant, gm/cm 3 = heat release per gram of reactant, ergs/gm = mixture specific heat ratio = specific heat ratio for species k = density, gm/cm 3 = density for species k, gm/cm 3 = induction parameter, gm/cm 3

The influence of acoustic impedance on gaseous layered detonations bounded by an inert gas

“…Instead, these triple points likely originate from the interaction between a Mach lens structure formed by a detached shock and the Mach stem of a detonation cell. Simulations of detonations propagating in RDEs corroborate this and often show detached shock structures [9,12,48] similar to the Mach lens structure shown in Figs. 11 and 12.…”

“…The high-pressure produced by the detonation transmits an oblique shock into the products. A detached wave structure, qualitatively similar to Case 5, is often observed in numerical simulations of RDEs [9,12,48] due to the high sound speed of the products. A hydrodynamically unstable slip line forms at the contact surface that separates the products of the current detonation from the products of the previous detonation.…”

“…The main features and waves of an "unwrapped" RDE combustor based on numerical simulations[9,12,48]. The left and right boundaries are periodic.…”