HiFi-TURB-DLR rounded step

Semi-confined Flows

Underlying Flow Regime 3-36

Abstract

The Underlying Flow Regime (UFR) studied here, is a Turbulent Boundary layer (TBL) subjected to an adverse pressure gradient (APG) inducing flow separation on a smooth curved surface. The physically and industrially significant flow phenomenon remains challenging to predict with state-of-the-art RANS turbulence models despite the numerous existing experimental and numerical studies. Popular examples are the 2D NASA Wall-mounted Hump of Greenblatt et al. [‌1][‌2] as well as the curved backward facing step (see UFR 3-31 Test Case)[‌3][‌4] . For both cases, experimental data, LES/DNS-data as well as results from RANS turbulence models exist [‌4][‌5].

In contrast to the latter cases, the UFR described here was designed as a purely numerical test case that cannot be directly transferred to a wind tunnel experiment. The geometry is part of a study comprising four different geometries, each computed with two different Reynolds numbers ( ${Re_{H}=78,490}$ and ${Re_{H}=136,504}$ ) based on the step height $H$ . The objective is to provide a test case suitable for DNS computations in order to generate a comprehensive database that can be exploited by data-driven approaches employing Machine Learning (ML). The final design of this UFR testcase is based on a study applying several state-of-the-art Reynold-Averaged Navier-Stokes (RANS) models as well as an experimental test case designed by NASA [‌6].

From the four different configurations designed by the German Aerospace Center (DLR) for the purpose and the two different Reynolds numbers, only one test case is discussed here. The configuration presents a moderate APG which results in a flow incipient to separation in the step region. For this configuration RANS simulations are performed using a Differential Reynolds Stress model by DLR and a two-equation model by the University of Bergamo (UNIBG). The results of both RANS computations are subsequently compared to an under-resoved numerical simulation (uDNS) performed by UNIBG and made available in DNS 1-5. The work presented here is part of the European project “HiFi-TURB”, that has received funding from the European Union’s Horizon 2020 research and innovation programs under grant agreement n° 814837.

Contributed by: Erij Alaya and Cornelia Grabe — Deutsches Luft-und Raumfahrt Zentrum (DLR)