Effects of confinement on absolute and convective instabilities for momentum-driven countercurrent shear layers

2021 ◽  
Vol 6 (7) ◽  
Author(s):  
Jinwei Yang ◽  
Matt J. Anderson ◽  
Paul J. Strykowski ◽  
Vinod Srinivasan
Keyword(s):  
Shear Layers ◽  
Convective Instabilities ◽  
Countercurrent Shear

Enhancing Combustion in a Dump Combustor Using Countercurrent Shear: Part 1 — Nonreacting Flow Control and Preliminary Combustion Results

2005 ◽  
Author(s):  
David J. Forliti ◽  
Alison A. Behrens ◽  
Paul J. Strykowski ◽  
Brian A. Tang
Keyword(s):  
Flow Control ◽  
Turbulent Combustion ◽  
Combustion Process ◽  
Shear Layers ◽  
Control Technique ◽  
Turbulence Energy ◽  
Mixing Enhancement ◽  
Length Scales ◽  
Dump Combustor ◽  
Countercurrent Shear

During the last decade, countercurrent shear has been established as an effective flow control technique for increasing turbulent mixing in a variety of flow configurations and operating regimes. Based on the robust mixing enhancement observed for jets and shear layers, the technique appears to have many potential benefits for enhancement and control for turbulent combustion flows. Countercurrent shear flow control has been applied to a planar asymmetric rearward-facing step dump combustor. A nonreacting flow study on the implementation of suction-based countercurrent shear at the dump plane provided insight into the flow control mechanisms. Control of turbulence velocity and length scales occurs through two mechanisms, the development of a countercurrent shear layer near the dump plane, and enhanced global recirculation caused by the removal of mass at the dump plane. Parametric studies on the geometry of the suction slot indicate that the enhancement of the global recirculation zone is the primary mechanism for increasing global turbulence levels within the combustor. Turbulence energy and length scales both increase in a manner such that the spatially-filtered strain rates as measured with particle image velocimetry remain nominally constant, a desirable characteristic for premixed turbulent combustion. Connections will be made to a recent study on fully-developed turbulent countercurrent shear layers showing additional attractive features of countercurrent shear including enhanced turbulent energy production, entrainment, and three dimensionality. Preliminary reacting flow results for the dump combustor operating while burning premixed/prevaporized JP-10 illustrate qualitative changes in the turbulent combustion process within the combustor. The companion paper will describe the quantitative effects of countercurrent shear on the global heat release rates within the combustor.

scholarly journals Absolute and convective instabilities in open shear layers

2003 ◽  
Vol 413 (1) ◽  
pp. 7-15 ◽  
Author(s):  
M. Terra-Homem ◽  
R. Erdélyi
Keyword(s):  
Shear Layers ◽  
Convective Instabilities

scholarly journals Absolute and convective instabilities in open shear layers

2003 ◽  
Vol 403 (2) ◽  
pp. 425-432 ◽  
Author(s):  
M. Terra-Homem ◽  
R. Erdélyi
Keyword(s):  
Shear Layers ◽  
Convective Instabilities

Vectoring Thrust in Multiaxes Using Confined Shear Layers

1999 ◽  
Vol 122 (1) ◽  
pp. 3-13 ◽  
Author(s):  
F. S. Alvi ◽  
P. J. Strykowski ◽  
A. Krothapalli ◽  
D. J. Forliti
Keyword(s):  
Shear Layer ◽  
Mass Flow ◽  
Shear Layers ◽  
Continuous Control ◽  
Primary Flow ◽  
Flow Rates ◽  
Thrust Vector ◽  
Mass Flow Rates ◽  
Countercurrent Shear ◽  
Thrust Performance

A fluidic scheme is described which exploits a confined countercurrent shear layer to achieve multiaxis thrust vector response of supersonic jets in the absence of moving parts. Proportional and continuous control of jet deflection is demonstrated at Mach numbers up to 2, for pitch vectoring in rectangular nozzles and multiaxis vectoring in axisymmetric nozzles. Secondary mass flow rates less than approximately 2% of the primary flow are used to achieve thrust vector angles exceeding 15 degrees. Jet slew rates up to 180 degrees per second are shown, and the fluidic scheme is examined in both static and wind-on configurations. Thrust performance is studied for external coflow velocities between Mach 0.3 and 0.7. [S0098-2202(00)02601-8]

Vectoring thrust using confined countercurrent shear layers

1997 ◽  
Author(s):  
P. Strykowski ◽  
G. Schmid ◽  
F. Alvi ◽  
A. Krothapalli ◽  
P. Strykowski ◽  
...  
Keyword(s):  
Shear Layers ◽  
Countercurrent Shear

The effect of counterflow on the development of compressible shear layers

1996 ◽  
Vol 308 ◽  
pp. 63-96 ◽  
Author(s):  
P. J. Strykowski ◽  
A. Krothapalli ◽  
S. Jendoubi
Keyword(s):  
Shear Layer ◽  
High Speed ◽  
Reverse Flow ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Shear Layers ◽  
Enhanced Diffusion ◽  
Spatio Temporal ◽  
Density Ratios ◽  
Countercurrent Shear

A compressible countercurrent shear layer was investigated experimentally by establishing reverse flow around the perimeter of a supersonic jet. Measurements demonstrate that spatial growth rates of the countercurrent shear layer significantly exceed those of the classical coflowing layer at comparable density ratios and levels of compressibility. Experiments also reveal the presence of coherent three-dimensional structures in the countercurrent shear layer at convective Mach numbers where similar structures are not present in coflowing layers. It is argued that these kinematic differences are responsible for the enhanced diffusion of the shear layer with counterflow. The spatio-temporal theory is used to examine the connection between the experimental observations and the existence of a transition from convective to absolute instability in high-speed shear layers.

The Structures of the Shear Layers in Box Shear Test of Soil

Landslides ◽  
1994 ◽  
Vol 31 (1) ◽  
pp. 10-20_1
Author(s):  
Ryojiro KISHIMOTO
Keyword(s):  
Shear Test ◽  
Shear Layers

Analysis of shear bands in slow granular flows using a frictional Cosserat model

2000 ◽  
Vol 627 ◽  
Author(s):  
Prabhu R. Nott ◽  
K. Kesava Rao ◽  
L. Srinivasa Mohan
Keyword(s):  
Scaling Laws ◽  
Shear Bands ◽  
Shear Layers ◽  
Theoretical Description ◽  
Field Variable ◽  
Cosserat Continuum ◽  
Momentum Balance ◽  
Rigid Plastic ◽  
Independent Field ◽  
Cosserat Model

ABSTRACTThe slow flow of granular materials is often marked by the existence of narrow shear layers, adjacent to large regions that suffer little or no deformation. This behaviour, in the regime where shear stress is generated primarily by the frictional interactions between grains, has so far eluded theoretical description. In this paper, we present a rigid-plastic frictional Cosserat model that captures thin shear layers by incorporating a microscopic length scale. We treat the granular medium as a Cosserat continuum, which allows the existence of localised couple stresses and, therefore, the possibility of an asymmetric stress tensor. In addition, the local rotation is an independent field variable and is not necessarily equal to the vorticity. The angular momentum balance, which is implicitly satisfied for a classical continuum, must now be solved in conjunction with the linear momentum balances. We extend the critical state model, used in soil plasticity, for a Cosserat continuum and obtain predictions for flow in plane and cylindrical Couette devices. The velocity profile predicted by our model is in qualitative agreement with available experimental data. In addition, our model can predict scaling laws for the shear layer thickness as a function of the Couette gap, which must be verified in future experiments. Most significantly, our model can determine the velocity field in viscometric flows, which classical plasticity-based model cannot.

Vortical substructures in the shear layers forming leading-edge vortices

AIAA Journal ◽  
2002 ◽  
Vol 40 ◽  
pp. 1689-1692 ◽  
Author(s):  
A. M. Mitchell ◽  
P. Molton
Keyword(s):  
Leading Edge ◽  
Shear Layers ◽  
Leading Edge Vortices
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