Progress in shock wave/boundary layer interactions

Rice husk (RH) has now become a source for a number of silicon compounds, including silicon carbide, silica, silicon nitride, silicon tetrachloride, zeolite, and pure silicon. The applications of such materials derived from rice husks are very comprehensive. The methods of synthesizing these silicon-based materials from RHs and their applications are reviewed in this paper.

Silicon-Based Materials from Rice Husks and Their Applications

The relationship between the upstream boundary layer and the low-frequency, large-scale unsteadiness of the separated flow in a Mach 2 compression ramp interaction is investigated by performing wide-field particle image velocimetry (PIV) and planar laser scattering (PLS) measurements in streamwise–spanwise planes. Planar laser scattering measurements in the upstream boundary layer indicate the presence of spanwise strips of elongated regions of uniform momentum with lengths greater than 40?. These long coherent structures have been observed in a Mach 2 supersonic boundary layer (Ganapathisubramani, Clemens & Dolling 2006) and they exhibit strong similarities to those that have been found in incompressible boundary layers (Tomkins & Adrian 2003; Ganapathisubramani, Longmire & Marusic 2003). At a wall-normal location of y/?=0.2, the inferred instantaneous separation line of the separation region is found to oscillate between x/?=?3 and ?1 (where x/?=0 is the ramp corner). The instantaneous spanwise separation line is found to respond to the elongated regions of uniform momentum. It is shown that high- and low-momentum regions are correlated with smaller and larger size of the separation region, respectively. Furthermore, the instantaneous separation line exhibits large-scale undulations that conform to the low- and high-speed regions in the upstream boundary layer. The low-frequency unsteadiness of the separation region/shock foot observed in numerous previous studies can be explained by a turbulent mechanism that includes these elongated regions of uniform momentum

Effects of upstream boundary layer on the unsteadiness of shock induced separation

This paper presents the results of a detailed hydrodynamic study of a row of inclined jets issuing into a crossflow with a density ratio of injectant to freestream of two. Laser Doppler anemometry was used to measure the vertical and streamwise components of velocity for a jet-to-freestream mass flux ratio of 0.5. Mean velocity components and turbulent Reynolds normal and shear stress components were measured at locations in a vertical plane along the centerline of the jet from 1 diameter upstream to 30 diameters downstream of the jet. The results, which have application to film cooling, give a quantitative picture of the entire flow field, from the approaching flow upstream of the jet, through the interaction region of the jet and freestream, to the relaxation region downstream where the flow field approaches that of a standard turbulent boundary layer.Copyright © 1989 by ASME

Effects of density ratio on the hydrodynamics of film cooling

Cold spraying is increasingly attracting attentions from both scientific and industrial communities due to its unique ‘low-temperature’ coating build-up process and its potential applications in the additive manufacturing across a variety of industries. The existing studies mainly focused on the following subjects: particle acceleration and heating, coating build-up, coating formation mechanism, coating properties, and coating applications, among which particle acceleration and heating can be regarded as the premise of the other subjects because it directly determines whether particles have sufficient energy to deposit and form the coating. Investigations on particle acceleration and heating behavior in cold spraying have been widely conducted both numerically and experimentally over decades, where many valuable conclusions were drawn. However, existing literature on this topic is vast; a systematical summery and review work is still lack so far. Besides, some curtail issues involved in modeling and experiments are still not quite clear, which needs to be further clarified. Hence, a comprehensive summary and review of the literature are very necessary. In this paper, the gas flow, particle acceleration, and heat transfer behavior in the cold spray process are systematically reviewed. Firstly, a brief introduction is given to introduce the early analytical models for predicting the gas flow and particle velocity in cold spraying. Subsequently, special attention is directed towards the application of computational fluid dynamics technique for cold spray modeling. Finally, the experimental observations and measurements in cold spraying are summarized.

Gas Flow, Particle Acceleration, and Heat Transfer in Cold Spray: A review

An experimental investigation was conducted to control the amplitude of shock unsteadiness associated with a 24 deg compression-ramp-induced interaction in a Mach 2 flow.Two control configurations in the form of an array of
1) 16 90-deg-pitched steady micro-air-jet vortex-generating devices (AJVG1), and 2) eight pairs of 45-deg-pitched
steady micro-air-jet vortex-generating devices (AJVG2) were studied. EachAJVGdevice was placed upstream of the
interaction region at 12:5� from the compression corner. Both micro-AJVG configurations show a reduction in
separation shock strength and help considerably reduce the height of the lambda-wave triple point with increase in
Poj . Pitching the microjets at 45 deg, as in the AJVG2 configuration, prevents a stronger control-generated bow shock to form ahead of the injectors and, hence, reduces the obstruction component of the interaction significantly. A well defined separation line for no control is seen to get replaced by a highly corrugated separation line with control. Significant reduction (up to 67%) in the peak rms value is observed in the intermittent region of separation with AJVG1 for Poj � 208:5 kPa while the same is achieved with AJVG2 at a much higher Poj�>500 kPa�. The spectral
content of the pressure fluctuations also indicate that, relative to the AJVG2 configuration, AJVG1 is successful in
reducing the amplitude of fluctuations in the range of unsteadiness by an order of magnitude as soon as Poj exceeds
208.5 kPa. The amplitude of these fluctuations is seen to further decrease with increase in Poj.

Shockwave/Boundary-Layer Interaction Control on a Compression Ramp Using Steady Micro Jets

An experimental investigation has been carried out to study the performance and base pressure characteristics of a Mach 2.0 annular conical aerospike nozzle with and without freestream flow. The effect of cowl length, plug length, and plug contour variation on the nozzle performance and base pressure characteristics is studied. It is observed that the overexpansion shock from the internal nozzle, overexpansion shock on the spike surface, and the expansion fan from the cowl lip of the internal nozzle dominate the overall flowfield development. The presence of freestream flow reduces the nozzle performance by approximately 4% relative to static conditions. Base pressure characteristics are observed to be strongly influenced by the movement of these shocks on the plug surface, and their subsequent interaction with the inner shear layer controls the base-wake closure. Relative to the conical plug conflguration, the contoured plug shows considerably enhanced base pressure characteristics. Real-time pressure measurements on the spike reveal highly unsteady flow in the intermittent region of separation.

Performance Characteristics of an Annular Conical Aerospike Nozzle with Freestream Effect

Relation between shock unsteadiness and the origin of side-loads inside a thrust optimized parabolic rocket nozzle

An experimental investigation has been carried out on a subscale thrust optimized parabolic nozzle (area ratio of
30) to study the flow characteristics prevalent during a partially formed restricted shock separation and a fully
formed restricted shock separation condition, each of which are observed to be discrete in nature Whereas the wall
pressure signal near the nozzle exit randomly alternates between its value in the backflow region and that above
ambient (ie, flow randomly alternates between a free shock separation and restricted shock separation transition
condition and vice versa) as a function of time for a partially formed restricted shock separation condition, the wall
pressure in a fully formed restricted shock separation condition fluctuates in values above ambient in the region of
flow reattachment Further, the transient conditions of free shock separation to partially formed restricted shock
separation and end-effect regime are studied in detail The preceding transitions and retransitions suggest a variation
in the relative axial positions of normal and separation shocks that favors a fully formed restricted shock separation
to occur during shutdown A second separation bubble is also observed in the restricted shock separation condition, the formation and opening of which is seen to contribute toward side-load peaks Results also indicate that the separation shock translates back and forth (flapping motion) and experiences spanwise perturbations (rippling motion) The results are based on simultaneously acquired real-time wall pressure measurements, surface oil visualization technique, high-speed schlieren images, and signals from strain gauges installed on the nozzle bending tube

Shashi B. Verma

Papers

Shockwave/Boundary-Layer Interaction Control on a Compression Ramp Using Steady Micro Jets

Performance Characteristics of an Annular Conical Aerospike Nozzle with Freestream Effect

Relation between shock unsteadiness and the origin of side-loads inside a thrust optimized parabolic rocket nozzle

Study of Restricted Shock Separation Phenomena in a Thrust Optimized Parabolic Nozzle

Numerical study of shock/boundary layer interaction in supersonic overexpanded nozzles