Weak-Shock Interactions with Transonic Laminar Mixing Layers of Fuels for High-Speed Propulsion

The flow over a cavity at a Mach number 0.8 is considered. The cavity is deep with an aspect ratio (length over depth) L/D = 0.42. This deep cavity flow exhibits several features that makes it different from shallower cavities. It is subjected to very regular self-sustained oscillations with a highly two-dimensional and periodic organization of the mixing layer over the cavity. This is revealed by means of a high-speed schlieren technique. Analysis of pressure signals shows that the first tone mode is the strongest, the others being close to harmonics. This departs from shallower cavity flows where the tones are usually predicted well by the standard Rossiter’s model. A two-component laser-Doppler velocimetry system is also used to characterize the phase-averaged properties of the flow. It is shown that the formation of coherent vortices in the region close to the boundary layer separation has some resemblance to the ‘collective interaction mechanism’ introduced by Ho & Huang (1982) to describe mixing layers subjected to strong sub-harmonic forcing. Otherwise, the conditional statistics show close similarities with those found in classical forced mixing layers except for the production of random perturbations, which reaches a maximum in the structure centres, not in the hyperbolic regions with which turbulence production is usually associated. An attempt is made to relate this difference to the elliptic instability that may be observed here thanks to the particularly well-organized nature of the flow.

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Model for compressible turbulence in hypersonic wall boundary and high-speed mixing layers

AIAA Journal ◽

10.2514/3.12224 ◽

1994 ◽

Vol 32 (7) ◽

pp. 1531-1533 ◽

Cited By ~ 4

Author(s):

Rodney D. W. Bowersox ◽

Joseph A. Schetz

Keyword(s):

High Speed ◽

Mixing Layers ◽

Compressible Turbulence ◽

Wall Boundary

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Computations of Nonlinear Propagation of Sound Emitted from High Speed Mixing Layers~!2009-10-22~!2010-02-25~!2010-05-04~!

The Open Acoustics Journal ◽

10.2174/1874837601003010011 ◽

2010 ◽

Vol 3 (1) ◽

pp. 11-20 ◽

Cited By ~ 3

Author(s):

J. Punekar ◽

E. J. Avital ◽

R. E. Musafir

Keyword(s):

High Speed ◽

Mixing Layers ◽

Nonlinear Propagation

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An experimental investigation of the effects of compressibility on a turbulent reacting mixing layer

Journal of Fluid Mechanics ◽

10.1017/s002211209700791x ◽

1998 ◽

Vol 356 ◽

pp. 25-64 ◽

Cited By ~ 26

Author(s):

M. F. MILLER ◽

C. T. BOWMAN ◽

M. G. MUNGAL

Keyword(s):

High Speed ◽

Large Scale ◽

Structural Changes ◽

Density Ratio ◽

Mixing Layer ◽

Mixing Layers ◽

Unexpected Result ◽

Entrainment Ratio ◽

Plan View ◽

Compressible Mixing Layer

Experiments were conducted to investigate the effect of compressibility on turbulent reacting mixing layers with moderate heat release. Side- and plan-view visualizations of the reacting mixing layers, which were formed between a high-speed high-temperature vitiated-air stream and a low-speed ambient-temperature hydrogen stream, were obtained using a combined OH/acetone planar laser-induced fluorescence imaging technique. The instantaneous images of OH provide two-dimensional maps of the regions of combustion, and similar images of acetone, which was seeded into the fuel stream, provide maps of the regions of unburned fuel. Two low-compressibility (Mc=0.32, 0.35) reacting mixing layers with differing density ratios and one high-compressibility (Mc=0.70) reacting mixing layer were studied. Higher average acetone signals were measured in the compressible mixing layer than in its low-compressibility counterpart (i.e. same density ratio), indicating a lower entrainment ratio. Additionally, the compressible mixing layer had slightly wider regions of OH and 50% higher OH signals, which was an unexpected result since lowering the entrainment ratio had the opposite effect at low compressibilities. The large-scale structural changes induced by compressibility are believed to be primarily responsible for the difference in the behaviour of the high- and low-compressibility reacting mixing layers. It is proposed that the coexistence of broad regions of OH and high acetone signals is a manifestation of a more biased distribution of mixture compositions in the compressible mixing layer. Other mechanisms through which compressibility can affect the combustion are discussed.

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An analysis of the particle trajectories in spherical blast waves reflected from real and ideal surfaces

Canadian Journal of Physics ◽

10.1139/p81-182 ◽

1981 ◽

Vol 59 (10) ◽

pp. 1380-1390 ◽

Cited By ~ 7

Author(s):

J. M. Dewey ◽

D. J. McMillin

Keyword(s):

High Speed ◽

Ground Surface ◽

Blast Waves ◽

Particle Trajectories ◽

Shock Interactions ◽

Pressure Time ◽

Time Histories ◽

Particle Velocities ◽

Spherical Shock ◽

Fixed Times

High speed photogrammetry has been used to measure the particle trajectories in the flows resulting from the interaction of two identical explosively produced spherical shock waves. It is postulated that the interaction simulated the reflection of a spherical shock from an ideal nonenergy-absorbing surface. The "ideal" reflections were compared with reflections from two types of ground surface. From the observed particle trajectories the particle velocities, gas densities, and hydrostatic, dynamic, and total pressures in the complex air flows behind the shock interactions have been computed. These flows are described as two dimensional fields at fixed times and as time histories at fixed locations. The Mach stem shocks at the ground surfaces were weaker than those at corresponding positions near the interaction planes, but the magnitudes of the flow properties in these waves decreased more slowly and, at later times, became greater than those in the waves at the interaction planes. Computed pressure–time histories were compared to measurements made using electronic transducers and good agreement was found.

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Double-pulse imaging using simultaneous OH/acetone plif for studying the evolution of high-speed, reacting mixing layers

Symposium (International) on Combustion ◽

10.1016/s0082-0784(06)80823-4 ◽

1994 ◽

Vol 25 (1) ◽

pp. 1743-1750 ◽

Cited By ~ 9

Author(s):

Jerry M. Seitzman ◽

Michael F. Miller ◽

Tobin C. Island ◽

Ronald K. Hanson

Keyword(s):

High Speed ◽

Double Pulse ◽

Mixing Layers

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Cooling of Turbine Blades With Expanded Exit Holes: Computational Analyses of Leading Edge and Pressure-Side of a Turbine Blade

Journal of Energy Resources Technology ◽

10.1115/1.4035829 ◽

2017 ◽

Vol 139 (4) ◽

Cited By ~ 8

Author(s):

Fariborz Forghan ◽

Omid Askari ◽

Uichiro Narusawa ◽

Hameed Metghalchi

Keyword(s):

High Speed ◽

Turbine Blades ◽

Leading Edge ◽

Weak Shock ◽

Suction Side ◽

Pressure Side ◽

Blade Surface ◽

Cooling Effectiveness ◽

Hot Gas ◽

Computational Analyses

Turbine blades are cooled by a jet flow from expanded exit holes (EEH) forming a low-temperature film over the blade surface. Subsequent to our report on the suction-side (low-pressure, high-speed region), computational analyses are performed to examine the cooling effectiveness of the flow from EEH located at the leading edge as well as at the pressure-side (high-pressure, low-speed region). Unlike the case of the suction-side, the flow through EEH on the pressure-side is either subsonic or transonic with a weak shock front. The cooling effectiveness, η (defined as the temperature difference between the hot gas and the blade surface as a fraction of that between the hot gas and the cooling jet), is higher than the suction-side along the surface near the exit of EEH. However, its magnitude declines sharply with an increase in the distance from EEH. Significant effects on the magnitude of η are observed and discussed in detail of (1) the coolant mass flow rate (0.001, 0.002, and 0.004 (kg/s)), (2) EEH configurations at the leading edge (vertical EEH at the stagnation point, 50 deg into the leading-edge suction-side, and 50 deg into the leading-edge pressure-side), (3) EEH configurations in the midregion of the pressure-side (90 deg (perpendicular to the mainstream flow), 30 deg EEH tilt toward upstream, and 30 deg tilt toward downstream), and (4) the inclination angle of EEH.

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