Modelling of natural and bypass transition in aerodynamics

Jiří Fürst,Petr Straka,Jaromír Příhoda

doi:10.1051/epjconf/20146702030

Abstract

Most of transition models are proposed for modelling of the bypass transition common in the internal aerodynamics especially in turbomachinery where free stream turbulence is the dominant parameter affecting the transition onset. Free-stream turbulence level in the external aerodynamics is usually noticeably lower and so the natural transition often occurs in flows around airfoils. The transition model with the algebraic equation for the intermittency coefficient proposed originally by Straka and P�ihoda (3) for the bypass transition was modified for modelling of the transition at low free-stream turbulence. The modification is carried out using experimental data of Schubauer and Skramstad (18). Further, the three-equation k-kL- model proposed by Walters and Cokljat (10) was used for the modelling of the transition at low free-stream turbulence. Both models were tested by means of the incompressible flow around airfoils at moderate and very low free-stream turbulence.

Highlights

The modelling of the laminar/turbulent transition is crucial for the adequate simulation of flows in internal and external aerodynamics, especially for flows around blades and airfoils where substantially influences the prediction of energy losses and heat transfer
The Reynolds-averaged Navier-Stokes equations are closed partly by the explicit algebraic Reynolds stress turbulence model (EARSM) according to Hellsten [9] connected with the algebraic transition model modified by Straka and PĜíhoda [3] and partly by the threeequation k-kL-Z model of Walters and Cokljat [10]
The transition models were tested by means of the incompressible flow around airfoils at relatively low freestream turbulence

Summary

Introduction

The modelling of the laminar/turbulent transition is crucial for the adequate simulation of flows in internal and external aerodynamics, especially for flows around blades and airfoils where substantially influences the prediction of energy losses and heat transfer. Most of transition models are based on the transport and/or algebraic equation for the intermittency coefficient (see e.g. Langtry and Menter [1], Lodefier and Dick [2], Straka and PĜíhoda [3]). The so-called en method based on the linear stability theory is often used for low freestream turbulence flows in aeronautics (see Drela and Giles [4], Stock and Haase [5]), but this method cannot do without a relation between the critical amplification factor n and free-stream turbulence Tu. Besides, threeequation k-kL-Z model by Walters and Leylek [6] with the equation for the energy of non-turbulent fluctuations can be used for modelling of the natural and bypass transition as well

Mathematical model

Algebraic transition model

Results

Conclusions