The study of mesh quality influence on the location of boundary layer transition over a swept wing

Аuthors

Platonov I. M.^*, Bykov L. V.^**

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: platonov@mai.ru
**e-mail: bykovlv@mai.ru

Abstract

While performing mathematical modeling, it is imperative to have in mind the inherent inaccuracy of numerical methods and the precision of the solution, which depends on the finite elements discretization. In this paper the influence of mesh quality on results accuracy will be studied based on the case of fluid flow over a swept wing NFL(2)-0415. A series of experiments were performed on a wing with above mentioned profile in the Arizona State University.

To perform a mathematical modeling a system of Navier-Stokes equations and a turbulence model were used. In this instance the turbulence was modeled using the intermittency model.

To estimate mesh quality the location of boundary layer transition along the chord length was determined by the intermittency parameter. When intermittency equals 0 the flow is considered laminar, when it equals 1 — it is fully turbulent. Results acquired during CFD modeling were compared to experimental data.

An important factor to consider is the local wall distance y+, a parameter which signifies the normal distance fr om the surface to the center of first cell. The correct description of boundary layer highly depends on such parameter, which, consequently, affects flow regime and aerodynamic parameters, such as lift and drag.

Three different sizes of mesh were reviewed. A mesh independent solution was achieved, wh ere the results stopped improving with increasing mesh size. These sizes were 1.4 and 2.3 million elements, with the appropriate local wall distance y+<10.

It is a good practice to always perform mesh independence studies whenever mathematical modeling is involved. Mesh quality criterion such as y+ must be applied to cases of near wall flows, i.e. the boundary layer flow.

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