Experimental investigation on transverse jet penetration into a supersonic turbulent crossflow

The paper evaluates the evolvement of coherent structures and penetration height of gaseous transverse jet penetration into a supersonic turbulent flow.The high spatiotemporal resolution coherent structures of the jet plume are obtained by utilizing the nanoparticle-based planar laser scattering technique(NPLS).The evolving pattern of the coherent structures generated on the upwind surface of the transverse jet is analyzed based on the NPLS images.The shedding eddies from the jet near-field have lower convection velocity along freestream direction,while vortex growth rate is apparently higher than the far-field.Farther downstream,the large-scale eddies have less deformation and translate at velocities near the freestream velocity.Thus the near-field determines the scale of eddies in the far-field and affects the whole mixing process.The effect of injection stagnation pressure on the coherent structures is discussed and a modified penetration correlation is proposed based on an edge approximation definition and least square method with various injection pressures.

EXPERIMENTAL STUDY ON THE VORTEX FORMATION AND ENTRAINMENT CHARACTERISTICS FOR A ROUND TRANSVERSE JET IN SHALLOW WATER

The vortex formation and entrainment characteristics for a round transverse jet in shallow water were experimentally investigated by means of a combination of LIF flow visualization and PIV measurement. A scarf vortex wrapped around the main body of the jet is formed in the near-wall region due to the interaction between the resulting wall jet and sufficiently shallow crossflow, with some more or less unsteady flow properties and with spreading ranges as functions of both the velocity ratio and the water depth within the near field. The entrainment of the ambient crossflow fluid into the jet main body is closely associated with the time-evolving features of the shear layer between the jet and surrounding fluid as well as the induced vortical structures near the wall. In the case of slight impingement upon the wall, the interaction between the jet shear layer and the weak, unstable scarf vortex gives rise to an appreciable local entrainment enhancement, confined in the near-wall region in the vicinity of the stagnation point. While in the case of intense impingement upon the wall, the well-organized and stable scarf vortex gives rise to a greatly enhanced entrainment and a greatly increased lateral spreading rate nearly throughout the overall near field as compared to the conventional wall jet. In addition, the entrainment of the ambient crossflow fluid by the scarf vortex in this case occurs largely on the surface of the unique spiral roller structure by itself due to the presence of smaller and unorganized eddies, and accordingly the scarf vortex is likely to keep its spiral roller structure steadily to a relatively great downstream distance within the near field.

Numerical investigation on jet interaction with a compression ramp

A numerical investigation on jet interaction in supersonic laminar flow with a compres- sion ramp is performed utilizing the AUSMDV scheme and a parallel solver. Several parameters dominating the interference flowfield are studied after defining the relative increment of normal force and the jet amplification factor as the evaluation criterion of jet control performance. The computational results show that most features of the interaction flowfield between the transverse jet and the ramp are similar to those between a jet and a flat plate, except that the flow structures are more complicated and the low-pressure region behind the jet is less extensive. The relative force increment and the jet amplification factor both increase with the distance between the jet and the ramp shortening till quintuple jet diameters. Inconspicuous difference is observed between the jet-before-ramp and jet-on-ramp cases. The variation of the injection angle changes the extent of the separation region, the plateau pressure, and the peak pressure near the jet. In the present computational conditions, 120 is indicated relatively optimal among all the injection angles studied. For cold gas simulations, although little influence of the jet temperature on the pressure distribution near the jet is observed under the computation model and the flow parameters studied, reducing jet temperature somehow benefits the improvement of the normal force and the jet efficiency. When the pressure ratio of jet to freestream is fixed, the relative force increment varies little when increasing the freestream Mach number, while the jet amplification factor increases.

Accelerated initiation of oblique detonation induced by disturbance in detonative zone

In the real flow for high altitude,the initiation mechanism of the oblique detonation involves the coupling of complex wave structures and combustion waves,which may result in the phenomenon of extinction.The approach of stable initiation is one of the key factors that restricting the oblique detonation engine from theory to practice.The wave structure,initiation characteristics and characteristic parameters of the flow field are analyzed,the two-dimensional Euler equation considering the detailed chemical reactions of multi-component are solved.First,the approaches of blunt bump and transverse jet are combined used to shorten the detonation distance of the oblique detonation.Results show that these methods can promote the accelerated initiation of the oblique detonation effectively,and the detonation distance can be shortened more than 90%.There are two wave structures induced by the blunt bump:weak coupled and strong coupled,adding the transverse jet promotes the transition between these two wave structures.Then,the shape of the bump and the characteristic parameters of the transverse jet are optimized.The streamline-shape bump can eliminate the recirculation zone formed after the circle bump and the ellipse bump.The transverse jet will produce an oblique detonation wave at the front of the jet position,which changes the wave structure and initiation mode of the oblique detonation wave.It is expected to reveal the accelerated initiation mechanism of oblique detonation under the induction zone disturbance and complex flow environment,deepen the understanding of the detonation law of oblique detonation wave under real flow conditions,and provide a scientific basic for the development of the combustor of the oblique detonation engine.