Flow Enthalpy Effects On Scramjet Mixing And Combustion


The three-dimensional nature of the mixing process in a scramjet combustor is analyzed by examining the stream- wise vorticity-driven macro-mixing as well as the shear- driven small scale mixing. First, results of the numerical simulation of 15 degree downstream helium injection into a unconfined Mach 6 airstream are discussed. Details of downstream mixing and mean flow are in good agreement with experimental data. Results of the numerical simulation of similar hydrogen injection into a high enthalpy (Mach 17) confined Mach 6 airstream are then presented. The low enthalpy inflow from the unconfined case was then provided to the high enthalpy geometry in order to study the feasibility of using low enthalpy simulations of mixing for scramjet flight performance estimation. Results indicate that the mixing is substantially lower for the high enthalpy case. Production and decay of axial vorticity, cross-flow velocities, and the mean-flow velocities of these confined flows are related and discussed to illustrate the effect of residence time on jet mixing. The concept of lifting length (the effective distance an average fluid particle travels in the cross-flow direction over the combustor length) is introduced in order to explain the important contribution of axial vorticity to mixing in both high and low enthalpy flows. Scaling laws and suggestions for scaling improvements for actual three dimensional vortical scramjet combustors are discussed.


Mechanical and Aerospace Engineering

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Article - Conference proceedings

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Publication Date

01 Jan 1992