Entropy Generation in Steady Laminar Boundary Layers with Pressure Gradients

Abstract

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

Entropy Generation for Bypass Transitional Boundary Layers

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Effect of Incidence Angle on Entropy Generation in the Boundary Layers on the Blade Suction Surface in a Compressor Cascade

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