J.C. Kok

Destabilizing Free Shear Layers in X-LES Using a Stochastic Subgrid-Scale Model

In this paper, a stochastic term is introduced in the subgrid-scale model of the X-LES method in order to improve the computation of turbulent free shear layers. These shear layers may develop too slowly in X-LES and similar DES-type methods, even when fine grids and high-order numerical methods are used. For a plane free shear layer, the stochastic subgrid-scale model induces rapid development of fully 3D turbulence in contrast to the standard method for which the flow remains purely 2D. A comparison is made with experimental results and with results of a zonal RANS–LES method with LES content added at the RANS–LES interface.

X-LES Simulations Using a High-Order Finite-Volume Scheme

This paper focuses on numerical aspects for hybrid RANS–LES computations using the X-LES method. In particular, the impact of using a high-order finite-volume scheme is considered. The finite-volume scheme is fourth-order accurate on non-uniform, curvilinear grids, has low numerical dispersion and dissipation, and is based on the skew-symmetric form of the compressible convection operator, which ensures that kinetic energy is conserved by convection. A limited grid convergence study is performed for the flow over a rounded bump in a square duct. The fourth-order results are shown to depend only mildly on the grid resolution. In contrast, second-order results require at least half the mesh size to become comparable to the fourth-order results. Additionally, the high-order method is extended with shock-capturing capability in such a way that interference with the subgrid-scale model is avoided. The suitability of this extension is demonstrated by means of a supersonic flow over a cavity.

Performance evaluation of gas turbine labyrinth seals using computational fluid dynamics

The paper presents an investigation on the characteristics of flow through labyrinth seals. The focus of the paper lies in the application of the Computational Fluid Dynamics (CFD) methodology. The Reynolds-Averaged Navier-Stokes equations are employed as the flow governing equations. Turbulence is incorporated through a variant of the two-equation k-ω turbulence model. Three test cases are considered. The first test case concerns a labyrinth seal configuration with a honeycomb land. The computational results are compared to those obtained from seal test rig measurements. The second test case addresses the same labyrinth seal where the honeycomb land is replaced by a solid smooth land. The third test case addresses the flow through a labyrinth seal with canted knives. The CFD method is considered as an analysis tool complementary to rig-testing and enables investigating the effect of new seal design features. Additionally CFD is seen as a tool to support the correct representation of test-data in semiempirical engineering models for seal design. An industrial perspective is presented towards the exploitation of these modeling capabilities for real-life design of seals.Copyright

A High-Order Finite-Volume Method with Block-Structured Local Grid Refinement

Time-dependent vortex-dominated flows are computed accurately with a high-order finite-volume method on structured grids. In order to attain the required grid resolution in the vortex region, block wise local grid refinement is employed. A new topology-based block refinement algorithm allows the efficient generation of such block-wise refined meshes. The high-order finite-volume method is extended with high-order interpolation to deal with the partially continuous grids at block interfaces that result from the refinement. Results are presented for three applications: one time-accurate RANS computation of a helicopter flow case and two hybrid RANS-LES computations of strongly separated flows.

Non-zonal Approaches for Grey Area Mitigation

The term non-zonal approach is applied in Go4Hybrid to refer to hybrid RANS-LES methods in which the model, not the user, defines the regions in which RANS and LES modes are active.

Aeroelastic Testcases in IDIHOM Project

In the IDIHOM Project three aeroelastic testcases have been calculated. Two of them - LANN Wing and DLR-F6 wing-body configuration - have been conducted by PUT. The last one, the HART II rotor has been prepared by NLR. Each partner has used different technology and software tools, hence each of the testcases describes the results of the simulation and technology which has been used.