Jet Injection into Supersonic Crossflow: Flowfield and Mixing studies
Abstract
Supersonic air-breathing engines or scramjets are perhaps the most important technological
hurdles towards the development of hypersonic transportation vehicles for both easy
access to space and for missile related applications. In these engines, the air entering the
combustor must remain supersonic, which significantly brings down the time available within
the engine for fuel-air mixing and combustion. There are many possible strategies for fuel
injection in such engines; the transverse jet injection into supersonic crossflow being one.
The principle parameter in jet in crossflow studies is the momentum flux ratio (J), which
is defined as the momentum flux ratio between the jet and the cross-flow. Compared to the
subsonic crossflow case, the supersonic crossflow has additional complexities due to the
presence of different shock structures in addition to the many different vortical structures.
The aim of the present work is to experimentally study the flowfield and mixing associated
with sonic jet injection into a supersonic crossflow. In addition to detailed flowfield
and mixing studies of the basic steady jet configuration, enhancement of mixing using a
newly developed passively modulated (injection) jet has also been studied. In the latter case,
a large range of jet modulation frequencies ( f ) characterized by the ratio of the modulation
frequency to the natural shear layer frequency ( f / fsl) have been investigated ( f / fsl = 0.12
to 1.31). In all cases, the flowfield is investigated using Particle Image Velocimetry (PIV)
to characterize the different flow features and the penetration of the jet into the crossflow.
Mixing studies have also been carried out using acetone Planar Laser Induced Fluorescence
(PLIF), with the injected jet containing acetone vapours, which is then tracked after injection
into the crossflow to quantify mixing.
In summary, the modulated jet shows significant changes in jet penetration, unsteady
motions of the jet, and the mixing of the jet into the crossflow. Among the large number of
cases studied, the penetration and the mixing are found to be higher at modulation frequencies
corresponding to the sub-harmonics of the shear layer frequency. The maximum penetration
is seen close to f / fsl = 0.26, but the maximum mixedness of the injected jet is seen to occur
at f / fsl = 0.46, where the penetration is higher than the base case, but not the highest