Patrick Queutey

Three-Dimensional Flow Computation with Reynolds Stress and Algebraic Stress Models

A quadratic explicit algebraic stress model (EASM) that takes into account the variation of production-to-dissipation rate ratio is compared with an implicit algebraic stress model (ASM) and with their parent Reynolds stress model (RSM) in this paper. A new implementation of ASM model where the turbulent eddy viscosity provided by the explicit solution is employed is found to be robust. Computations for ship flows at model and full scale are performed to assess the accuracy of different models. Explicit and implicit algebraic stress models give similar prediction for the flow investigated. The RSM model provides better prediction in the region dominated by convex curvature. However, no much improvement is observed near the concave surface.

RANS prediction of the KVLCC2 tanker in head waves

The present study is devoted to the computation of the KVLCC2 tanker in head wave with free heave and pitch motion. A RANS solver using finite-volume discretization and free-surface capturing approach is employed for the computation. Free ship motion is captured with a mesh deformation approach. Three different wave lengths (0.6Lpp, 1.1Lpp and 1.6Lpp) are computed. We focus on numerical uncertainty estimation in this paper. For each test case, three different meshes and at least three different time steps have been used to access both time and spatial discretization error. Additional computations with different setups aimed at identifying different numerical discretization errors will also be performed. It is demonstrated that special attention needs to be paid to time discretization. To keep the same time accuracy, time step needs to be reduced on fine mesh for such kind of unsteady free-surface computation involving important pitch or roll motion.

2-D COMPUTATIONS OF UNSTEADY FLOW PAST A SQUARE CYLINDER WITH THE BALDWIN-LOMAX MODEL

The unsteady turbulent flow past a square cylinder is calculated with the Baldwin-Lomax Model. The influence of the numerical schemes is studied. Comparisons with experimental data and with previous calculations using a Reynolds stress model and 3-D large eddy simulations are presented. It is shown that a good prediction is obtained with a Baldwin-Lomax model by using the recently proposed CPI discretization scheme.

Turbulent flow prediction around appended hulls

Two appended hull configurations have been simulated using all hexahedral unstructured grids. Numerical uncertainty is assessed with grid refinement. Influence of turbulence model and wall function approach have been investigated. Scale effect has been studied for one configuration. Numerical results are validated both with measurement data and with computational results using structured grid when possible.

A comparison between full RANSE and coupled RANSE-BEM approaches in ship propulsion performance prediction

The paper compares the development of the coupling between a viscous Reynolds-averaged Navier-Stokes (RANSE) method and an inviscid Boundary Element method (BEM) with application to the prediction of the propulsive performance of a propelled ship. The BEM computational model is implemented into the PRO-INS code developed by CNR-INSEAN. It is based on a boundary integral formulation for marine propellers in arbitrary onset non-cavitating and cavitating flow conditions. The RANSE approach is based on the unstructured finite-volume flow solver ISIS-CFD. An essential feature for full RANSE simulations with the ISIS-CFD code developed by ECN-CNRS is in the use of a sliding grid technique to simulate the real propeller rotating behind a ship hull. The STREAMLINE tanker and propeller are proposed as validation test case. Full RANSE simulations are performed for design speed only, while hybrid RANSE/BEM self-propulsion computations are performed for a speed range. Both computations are compared with experimental data and show good agreement for ship resistance and for propeller thrust and torque.Copyright

Numerical Study of the Turbulent Flow Around a Square Cylinder Near a Wall

Calculations are reported for the flow around a two-dimensional, square cylinder at Re = 22,000 (based on the prism side dimension, D, and the free-stream velocity) placed at various distances from an adjacent wall. The nominal boundary layer thickness is 1.5D. Experiments have indicated that unsteady vortex shedding is suppressed when the wall is relatively close to the cylinder. The turbulent fluctuations are simulated with three turbulence models: the one-equation model of Spalart & Allmaras (1992), the two-equations SST K–ω model (Menter, 1993) and a Reynolds stress Rij –ω closures (Deng & Visonneau, 1999). The paper consists in comparing simulation and experimental results for configurations S/D = 1 (periodic case) and S/D = 0.25 (stationary case). Predicted and measured distributions of the mean velocity, Reynolds stress tensor and surface pressures are compared. Although the agreement is very good in general, observed discrepancies are discussed.© 2002 ASME

Can adaptive grid refinement produce grid-independent solutions for incompressible flows?

Abstract This paper studies if adaptive grid refinement combined with finite-volume simulation of the incompressible RANS equations can be used to obtain grid-independent solutions of realistic flow problems. It is shown that grid adaptation based on metric tensors can generate series of meshes for grid convergence studies in a straightforward way. For a two-dimensional airfoil and the flow around a tanker ship, the grid convergence of the observed forces is sufficiently smooth for numerical uncertainty estimation. Grid refinement captures the details of the local flow in the wake, which is shown to be grid converged on reasonably-sized meshes. Thus, grid convergence studies using automatic refinement are suitable for high-Reynolds incompressible flows.

Creating Free-Surface Flow Grids with Automatic Grid Refinement

The objective of this work is to create grids for free-surface water flow simulation entirely with automatic grid refinement. It is shown why it is necessary to refine the mesh iteratively as the solution converges and why refinement and derefinement of hexahedral cells must be treated anisotropically.The proposed refinement criterion is a combination of the pressure Hessian with refinement at the free surface, in order to capture the flow which drives the surface motion and the position of the surface itself. Smoothing is needed in the computation of the Hessian in order to remove oscillations in the pressure, the pressure Hessian is extrapolated through the free surface to remove its discontinuity there.Two test cases confirm that effective fine meshes for wave computation can be created with the proposed automatic refinement procedure.

Sliding Grids and Adaptive Grid Refinement for RANS Simulation of Ship-Propeller Interaction

Abstract The paper describes a computational approach for a numerical propulsion test. Key techniques concern the computation of free-surface viscous flows around propellers using the sliding grid technique and accurate wave capturing around the hull. An advanced numerical technique resolves very small-scale flow motion such as tip vortex. Efficiency and accuracy are balanced using an adaptive mesh refinement technique. This approach is validated against the KCS test case proposed for the Tokyo 2005 and Gothenburg 2010 CFD validation workshops.

Wake Prediction of a Marine Propeller: The Role of the Turbulence Closures

The marine propeller is the principal ship component to provide the necessary propulsion and when working at the aft of a ship, the propeller operates in a heterogeneous field because of the wake, created by the hull, which can have an effect on performance since the interaction is directly related to vibrations, noise and propulsion performances. So, the physical mechanisms that characterize the interactions between the propeller and the hull is very complex.