Turbulent shear layers in confining channels

Benham, GP; Castrejón‐Pita, Alfonso A.; Hewitt, Ian; Please, Colin P.; Style, Robert W.; Bird, P. A. D.

doi:10.1080/14685248.2018.1459630

Cited by 5 publications

(14 citation statements)

References 38 publications

(60 reference statements)

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“…Wall drag is incorporated into the model with a friction factor, and the growth of the shear layers is modelled with a spreading parameter. As was shown by Benham et al [ 6 ], the model predictions have good agreement with both CFD and experimental work for a range of channel shapes and Reynolds numbers. We restrict our attention to slender diffuser shapes, since our model, which is based on integrated equations of mass and momentum, applies to long and thin domains which are slowly varying.…”

Section: Introductionsupporting

confidence: 78%

“…In this section, we describe the flow scenarios which we consider and outline the simple model, previously presented by Benham et al [ 6 ], which we use to describe these flows. This model is based on integrated conservation of mass and momentum equations in a long and thin geometry, as well as Bernoulli’s equation, which govern an idealised time-averaged flow profile.…”

Section: The Model and Optimal Control Problemmentioning

confidence: 99%

“…The simple model, presented by Benham et al [ 6 ], is used to describe the idealised flow profiles for each of the three cases. The first two cases share the same formulation, whilst the third case is slightly different.…”

Section: The Model and Optimal Control Problemmentioning

confidence: 99%

“…For these non-uniform flows which we consider, the development of the flow profile, which is fundamental to pressure recovery, can be described using a simple model for turbulent shear layers in confining channels [ 6 ]. The model assumes that the flow is composed of uniform streams separated by a linear shear layer.…”

Section: Introductionmentioning

confidence: 99%

“…The simple model which we use to describe the flow, was applied by Benham et al [ 6 ] to investigate pressure recovery of a simple class of diffuser shapes by exhaustively searching a restricted design space. When we widen the parameter space and treat the diffuser shape as a continuous control, it is necessary to seek more complex tools to solve the problem.…”

Section: Introductionmentioning

confidence: 99%

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Optimal control of diffuser shapes for non-uniform flow

et al. 2018

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A simplified model is used to identify the diffuser shape that maximises pressure recovery for several classes of non-uniform inflow. We find that optimal diffuser shapes strike a balance between not widening too soon, as this accentuates the non-uniform flow, and not staying narrow for too long, which is detrimental for wall drag. Three classes of non-uniform inflow are considered, with the axial velocity varying across the width of the diffuser entrance. The first case has inner and outer streams of different speeds, with a velocity jump between them that evolves into a shear layer downstream. The second case is a limiting case when these streams are of similar speed. The third case is a pure shear profile with linear velocity variation between the centre and outer edge of the diffuser. We describe the evolution of the time-averaged flow profile using a reduced mathematical model that has been previously tested against experiments and computational fluid dynamics models. The model consists of integrated mass and momentum equations, where wall drag is treated with a friction factor parameterisation. The governing equations of this model form the dynamics of an optimal control problem where the control is the diffuser channel shape. A numerical optimisation approach is used to solve the optimal control problem and Pontryagin’s maximum principle is used to find analytical solutions in the second and third cases. We show that some of the optimal diffuser shapes can be well approximated by piecewise linear sections. This suggests a low-dimensional parameterisation of the shapes, providing a structure in which more detailed and computationally expensive turbulence models can be used to find optimal shapes for more realistic flow behaviour.

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Section: Introductionsupporting

confidence: 78%

Section: The Model and Optimal Control Problemmentioning

confidence: 99%

Section: The Model and Optimal Control Problemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optimal control of diffuser shapes for non-uniform flow

et al. 2018

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Effects of shear layer growth on the indirect noise in compound nozzles

Younes

Hickey

2020

Journal of Sound and Vibration

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Vertical confinement effects on a fully developed turbulent shear layer

2022

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The effects of vertical confinement on a turbulent shear layer are investigated with large-eddy simulations of a freely developing shear layer (FSL) and a wall-confined shear layer (WSL) that develops between two horizontal walls. In the case of the WSL, the growth of the shear layer is inhibited by the walls. Once the walls prevent the development of the shear layer, highly anisotropic velocity fluctuations become prominent in the flow. These anisotropic velocity fluctuations are recognized as elongated large-scale structures (ELSS), whose streamwise length is much larger than the length scales in the other directions. Spectral analysis confirms that the turbulent kinetic energy is dominated by the ELSS, whose streamwise length grows continuously. A proper orthogonal decomposition can effectively extract a velocity component associated with the ELSS. The isotropy of the Reynolds stress tensor is changed by the presence of the ELSS. These changes in flow characteristics due to the ELSS are not observed in the FSL, where the shear layer thickness increases continuously. These behaviors of the WSL are consistent with those of stably stratified shear layers (SSSLs), where flow structures similar to ELSS also develop when the vertical flow development is confined by the stable stratification. The vertical confinement by the walls or stable stratification strengthens mean shear effects. The flow behavior at large scales in the WSL and SSSL is consistent with rapid distortion theory for turbulence subject to mean shear, suggesting that the development of ELSS is caused by the mean shear.

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Turbulent shear layers in confining channels

Cited by 5 publications

References 38 publications

Optimal control of diffuser shapes for non-uniform flow

Optimal control of diffuser shapes for non-uniform flow

Effects of shear layer growth on the indirect noise in compound nozzles

Vertical confinement effects on a fully developed turbulent shear layer

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