Numerical simulation of a turbulent wake subjected to adverse pressure gradient

Results are presented of high-fidelity scale-resolving simulations of the wake flow exposed to adverse pressure gradient (APG). Specifically, zonal RANS-IDDES computations are performed of the flow model designed and manufactured at the Technische Universität Braunschweig in the framework of a joint German-Russian project "Wake in Adverse Pressure gradient". The model includes a flat plate as the wake generator and two pairs of thin liner foils creating APG. Results of the computations of mean flow characteristics agree with currently available experimental data and differ from those of the RANS predictions. This suggests the necessity of RANS models improvement which is planned to be done with the use of the combined experimental/numerical database on the mean flow and turbulence statistics of the wake accumulated in the course of the project

Active Flow Separation Control on a High-Lift Wing-Body Configuration - Part 1: Baseline Flow and Constant Blowing

This paper describes the influence of grid resolution and turbulence modeling for a 3D transport aircraft in high lift configuration with massive flap separation. The flap is equipped with spanwise slotted active flow control (AFC) devices to allow studies on active separation control. The effects of constant slotted blowing on the high lift performance are highlighted. Oil flow pictures from a mid-scale experiment in the low speed wind tunnel of Airbus in Bremen (B-LSWT) serve as a validation database for the baseline CFD results. RANS calculations are carried out with and without constant blowing boundary conditions. The baseline flow is also investigated with a time-accurate URANS approach. One of the major outcomes of the AFC study is the demonstration of the feasibility to simulate AFC concepts on a 3D configuration. Constant blowing shows the beneficial effect that separation can largely be suppressed because of the energy added to the flow on the suction side of the flap. This study serves as a preceding validation for the subsequent pulsed blowing approach treated in Part 2

Active Flow-Separation Control on a High-Lift Wing-Body Configuration

This contribution discusses the implementation of active flow-separation control for a three-dimensional high-lift wing-body configuration under atmospheric low-speed wind-tunnel conditions. The slot actuators are applied on the suction side of the trailing-edge flap to prevent local flow separation. The experimental results indicate that the pulsed blowing flow control technique is effective on the present configuration with a global performance enhancement. Numerical investigations are the focus of this article. The baseline case is characterized by substantial portions of separated flow. Thus, the influence of grid resolution and turbulence modeling is investigated. Based on this an intermediate mesh in combination with the Shear Stress Transport model gives the best compromise between quality and computational turnaround times. The steady Reynolds Averaged Navier Stokes (RANS) calculations carried out with constant blowing demonstrate the feasibility to simulate active flow control concepts. The key flow control method is the pulsed blowing. The verification of the unsteady RANS approach with active flow control shows that high computational resources are required for consistent numerical evaluations. The computational results highlight the ability of pulsed blowing at moderate blowing momentum coefficients to suppress the flow separation on the trailing-edge flap. The numerical results show an acceptable agreement with the experiments

Prediction Capabilities of Two Reynolds Stress Turbulence Models for a Turbulent Wake Subjected to Adverse Pressure Gradient

The present contribution focuses on the behavior of two RANS Reynolds stress turbulence models in the prediction of flow reversal occurring in turbulent wakes subjected to strong adverse pressure gradients. RANS results are compared to a high-fidelity RANS-IDDES solution for an experimental set-up from Driver and Mateer. The tested models are the JHh-εh v2 and the SSG/LRR-ω. Additionally, the comparison includes a modified version of the SSG/LRR-ω model where the sensitivity to pressure gradients is enhanced by the Sε4 term, which is already present in the JHh-εh v2 model. None of these RANS approaches was able to capture the flow recirculation as shown by the IDDES. The analysis aims at characterizing the wake flow and identifying possible sources of the RANS shortcomings, such as departure from dynamic equilibrium and strong Reynolds stress anisotropy

A Strategy for RANS Turbulence Model Improvement

The vision and final goal of DLR’s guiding concept of a virtual aircraft is the highly accurate numerical and digital modelling of an aircraft with all its properties and components. This requires the development and maturation of highly accurate, cost-effective computing methods including simulation methods for external aerodynamic flows. On the one hand, the related flow regimes are characterized by very high Reynolds numbers. On the other hand, the design and optimization of an aircraft at full coverage of the flight envelope requires an extremely large number of simulations. Hence, the only cost-effective way of doing computational flow simulations is to apply the Reynolds Averaged Navier-Stokes (RANS) equations and the related RANS turbulence models. State-of-the-art RANS turbulence models are an integrated part of wing design for cruise flight, but reliability and maturity for computational flow simulations towards the borders of the flight envelope has not yet been achieved, for example, for the high-lift flow regime. The presentation will give an overview of the activities at the C²A²S²E department at DLR in terms of improving RANS turbulence models and understanding certain flow phenomena in high detail for flow simulations towards the borders of the flight envelope based on experimental and numerical high-fidelity data