Efficient Flow Solution Research Articles

Sensitivity of Rotorcraft Hover Predictions to Mesh Resolution in Strand Grid Framework

The strand grid approach is a flow solution method where a prismatic like grid using “strands” is grown to a short distance from the body surface to capture the viscous boundary layer and the rest of the domain is covered using an adaptive Cartesian grid. The approach offers a potential for nearly automatic grid generation and adaptation requiring very few input parameters while, at same time, offering the ability to obtain fast and efficient flow solution. This paper explores the sensitivity of rotor hover predictions to various meshing parameters in the strand grid framework. Surface mesh resolution has minimal impact on the predictions, whereas both the outer extent of the strand mesh and the Cartesian mesh resolution have significant effect on rotor performance and wake predictions. A strand mesh extending out to half a chord distance away and a Cartesian mesh spacing of less than two times the outer boundary spacing of the strand mesh are recommended for most rotor blade simulations.

Implementation Strategies for Accurate and Efficient Control Volume-Based Two-Phase Hydrothermal Flow Solutions

Numerical models of magmatic hydrothermal systems have become powerful tools for linking surface and seafloor observations to chemical and fluid-dynamic processes at depth. This task requires resolving multi-phase flow over large distances of several kilometers, a wide range of pressure (p) and temperature (T) conditions, and over timescales of several thousands of years. The key numerical challenge is that realistic simulations have to consider the high nonlinearity and strong coupling of the governing conservation equations for mass and energy, while also being numerically efficient so that the required spatial and temporal scales can be resolved. Here we outline possible solutions to this problem by evaluating different implementation strategies and presenting a numerical scheme for fully coupled accurate and efficient flow solutions. The general scheme, based on the Newton–Raphson (NR) method, is presented for the simplified case of 2-D pure water convection and uses a control volume discretization on unstructured meshes. We find that the presented techniques significantly reduce the computational effort with respect to sequential/decoupled schemes. Key to this is a theta-time-differencing method for better accuracy, stability and convergence behavior of the NR-iterations, as well as improvements regarding upwinding. These features make the presented methods useful for coupled simulations of magmatic hydrothermal systems and a potential basis for future 3-D multi-phase codes.

Cell-vertex Based Parallel and Adaptive Explicit 3D Flow Solution on Unstructured Grids

A parallel adaptive Euler flow solution algorithm is developed for 3D applications on distributed memory computers. Significant contribution of this research is the development and implementation of a parallel grid adaptation scheme together with an explicit cell vertex-based finite volume 3D flow solver on unstructured tetrahedral grids. Parallel adaptation of grids is based on grid-regeneration philosophy by using an existing serial grid generation program. Then, a general partitioner repartitions the grid. An adaptive sensor value, which is a measure to refine or coarsen grids, is calculated considering the pressure gradients in all partitioned blocks of grids. The parallel performance of the present study was tested. Parallel computations were performed on Unix workstations and a Linux cluster using MPI communication library. The present results show that overall adaptation scheme developed in this study is applicable to any pair of a flow solver and grid generator with affordable cost. It is also proved that parallel adaptation is necessary for accurate and efficient flow solutions.

Tide and Storm Surge Predictions Using Finite Element Model

A finite element (FE) model is used to study tides and hurricane storm surge in the Gulf of Mexico in the region ranging from the Mississippi Sound to the northwest coast of Florida. Issues that are emphasized include the use of large domains, the importance of a high degree of grid resolution in coastal regions of interest, the use of meshes with highly varying nodal densities to minimize the size of the discrete problem, and the use of the generalized wave‐continuity equation (GWCE) for FE‐based solutions to the shallow‐water equations. The computations presented are unprecedented in their scope, level of localized detail, and degree of grid‐size variability. The GWCE‐based FE model leads to very accurate and efficient flow solutions.