On The Use of Entropy to Predict Boundary Layer Stability

Walsh, Edmond J.; Davies, Mark; McEligot, Donald M.

doi:10.3390/e6040375

Cited by 3 publications

(2 citation statements)

References 19 publications

(22 reference statements)

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“…The basic hypothesis is that the turbulent boundary layer could be defined as the region where the local entropy generation rate caused by viscous dissipation is the most significant [19]. A novel entropy concept, named entropy increment ratio s vis , was proposed as follows:…”

Section: Sst-sdesmentioning

confidence: 99%

An Entropy-Assisted Shielding Function in DDES Formulation for the SST Turbulence Model

Zhou

Zhao

Shi

2017

Entropy

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Abstract:The intent of shielding functions in delayed detached-eddy simulation methods (DDES) is to preserve the wall boundary layers as Reynolds-averaged Navier-Strokes (RANS) mode, avoiding possible modeled stress depletion (MSD) or even unphysical separation due to grid refinement. An entropy function f s is introduced to construct a DDES formulation for the k-ω shear stress transport (SST) model, whose performance is extensively examined on a range of attached and separated flows (flat-plate flow, circular cylinder flow, and supersonic cavity-ramp flow). Two more forms of shielding functions are also included for comparison: one that uses the blending function F 2 of SST, the other which adopts the recalibrated shielding function f d_cor of the DDES version based on the Spalart-Allmaras (SA) model. In general, all of the shielding functions do not impair the vortex in fully separated flows. However, for flows including attached boundary layer, both F 2 and the recalibrated f d_cor are found to be too conservative to resolve the unsteady flow content. On the other side, f s is proposed on the theory of energy dissipation and independent on from any particular turbulence model, showing the generic priority by properly balancing the need of reserving the RANS modeled regions for wall boundary layers and generating the unsteady turbulent structures in detached areas.

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Section: Sst-sdesmentioning

confidence: 99%

An Entropy-Assisted Shielding Function in DDES Formulation for the SST Turbulence Model

Zhou

Zhao

Shi

2017

Entropy

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confidence: 99%

Entropy Generation in Steady Laminar Boundary Layers with Pressure Gradients

McEligot

Walsh

2014

Entropy

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In an earlier paper in Entropy [1] we hypothesized that the entropy generation rate is the driving force for boundary layer transition from laminar to turbulent flow. Subsequently, with our colleagues we have examined the prediction of entropy generation during such transitions [2,3]. We found that reasonable predictions for engineering purposes could be obtained for flows with negligible streamwise pressure gradients by adapting the linear combination model of Emmons [4]. A question then arises-will the Emmons approach be useful for boundary layer transition with significant streamwise pressure gradients as by Nolan and Zaki [5]. In our implementation the intermittency is calculated by comparison to skin friction correlations for laminar and turbulent boundary layers and is then applied with comparable correlations for the energy dissipation coefficient (i.e., non-dimensional integral entropy generation rate). In the case of negligible pressure gradients the Blasius theory provides the necessary laminar correlations.How can one conveniently predict C f {x} and C d {x} for pure laminar boundary layers with pressure gradients? (The nomenclature we use is defined by Walsh et al. [3].) One approach would be a full computational fluid dynamics (CFD) calculation with the turbulence model suppressed. An alternate approach is to employ the Thwaites integral technique [6,7] which can be programmed on a simple spread sheet. Then, if the local freestream velocity can be approximated by a power law, U ∞ {x} ~ x m , the correlations to be used in the Thwaites approach can be derived from Falkner-Skan solutions [7,8]. OPEN ACCESS

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Entropy Generation, or Exergy Destruction

Bejan

2016

Advanced Engineering Thermodynamics

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On The Use of Entropy to Predict Boundary Layer Stability

Cited by 3 publications

References 19 publications

An Entropy-Assisted Shielding Function in DDES Formulation for the SST Turbulence Model

An Entropy-Assisted Shielding Function in DDES Formulation for the SST Turbulence Model

Entropy Generation in Steady Laminar Boundary Layers with Pressure Gradients

Entropy Generation, or Exergy Destruction

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