Scramjet fuel-air mixing establishment in a pulse facility

Abstract

A numerical simulation of the temporally developing flow through a generic scramjet combustor duct is presented for stagnation conditions typical of flight at Mach 13. The particular focus is to examine the startup transients and to determine the time required for certain flow parameters to become established. The calculations were made with a Navier-Stokes solver SPARK with temporally relaxing inflow conditions derived from the operation of the T4 shock tunnel at the University of Queensland in Australia. The generic combustor geometry includes the injection of hydrogen fuel from the base of a centrally located strut. The flow was assumed laminar and fuel combustion was not included. The establishment process is presented for viscous parameters in the boundary layer and for parameters related to the fuel-air mixing.transient flow case, QV/fe / = fuel mass fraction f R = fuel mass fraction that is reactable G s = characteristic flow time k = thermal conductivity L c = characteristic length M = Mach number m R = mass flow ratio P = static pressure Pr = Prandtl number P s = stagnation or nozzle supply pressure Re = Reynolds number T = temperature T aw = adiabatic wall temperature t = time U c = characteristic velocity u = local velocity ;c, y = longitudinal and transverse coordinates y w = location of upper wall boundary, 0.02357 m 8 = boundary-layer thickness 8* = displacement thickness r\ m = mixing efficiency parameter 0 = momentum thickness p = mass density r e = establishment time 4> = fuel equivalence ratio boundary-layer edge conditions inflow plane conditions normalized values wall values Subscripts e = in = TV w = RIntroduction ESEARCH related to the operation of a scramjet engine at conditions corresponding to flight at. speeds above

An experimental investigation of an airframe integrated three-dimensional scramjet engine at a Mach 10 flight condition

“…Referring to Figure 3.19, the engine nozzle pressure takes approximately 1 ms to reach a steady normalised value after the peak value. 26 This time period corresponds to approximately 3 flow lengths based on the freestream velocity and model length and is consistent with previous studies (Jacobs et al, 1992;Rogers and Weidner, 1993). A consequence of using an identical test window for the entire engine is that different segments of the nozzle supply pressure trace are used to normalise each engine pressure data during the test time.…”

“…Dependent on the trigger delay, early injection can result in a signficant mass of fuel being injected prior to arrival of the test flow at the model. Previous experimental and numerical studies, such as those of Kirchhartz (2010, Figure 5.22) and Rogers and Weidner (1993), have indicated that early injection of fuel does not significantly affect the establishment of steady combustion within shock tunnel facilities. This was not the case for the current configuration and test condition.…”

Geometric scaling studies of an inlet-fuelled axisymmetric radical farming scramjet engine

“…This was undertaken for the first and final transducer on the 30 • transducer line and the location with the longest establishment time, always determined to be the final transducer, was determined to be the entire delay time, τ . This time, inclusive of the nozzle transit time, was always found to be greater than 3 body lengths of flow, in line with previous findings of Jacobs et al (1992) [103] and Rogers and Weidner (1993) [124].…”

“…The establishment time of steady flow in a scramjet engine and combustor has been investigated both experimentally and numerically by several researchers including Davies and Bernstein (1969) [123], Jacobs et al (1992) [103] and Rogers and Weidner (1993) [124], and is usually expressed as the ratio of the time to establish the steady flow to the time to traverse one model length, as shown in Equation 4.14.…”

“…Jacobs et al (1992) [103] simulated the transient to steady state establishment times of a scramjet combustor (non combusting) and found that in general G was approximately 0.9 for wall pressure measurements and approximately 3 for shear stress and heat flux data. A numerical study of scramjet air-fuel mixing by Rogers and Weidner (1993) [124] demonstrated that mixing reached quasi-stationary regime faster than the viscous effects of shear stress and heat transfer, thus implying that it takes the flow in a scramjet combustor approximately 3 body lengths to reach quasi-steady state.…”