Inlet conditions for large eddy simulation of gas-turbine swirl injectors

Copyright © 2008 American Institute of Aeronautics and AstronauticsIn this paper, we present a novel technique for generating swirl inlets for large eddy simulation. The velocity a short distance downstream of the inlet to the main domain is sampled and the flow velocity data are reintroduced back into the domain inlet, creating an inlet section integrated into the main domain in which turbulence can develop. Additionally, variable artificial body forces and velocity corrections are imposed in this inlet section, with feedback control to force the flow toward desired swirl, mean, and turbulent profiles. The method was applied to flow in an axisymmetric sudden expansion, with and without swirl at the inlet, and compared against experimental and literature large eddy simulation data and against similar results in the literature. The method generates excellent results for this case and is elegant and straightforward to implement

An LES Turbulent Inflow Generator using A Recycling and Rescaling Method

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.The present paper describes a recycling and rescaling method for generating turbulent inflow conditions for Large Eddy Simulation. The method is first validated by simulating a turbulent boundary layer and a turbulent mixing layer. It is demonstrated that, with input specification of mean velocities and turbulence rms levels (normal stresses) only, it can produce realistic and self-consistent turbulence structures. Comparison of shear stress and integral length scale indicates the success of the method in generating turbulent 1-point and 2-point correlations not specified in the input data. With the turbulent inlet conditions generated by this method, the growth rate of the turbulent boundary/mixing layer is properly predicted. Furthermore, the method can be used for the more complex inlet boundary flow types commonly found in industrial applications, which is demonstrated by generating non-equilibrium turbulent inflow and spanwise inhomogeneous inflow. As a final illustration of the benefits brought by this approach, a droplet-laden mixing layer is simulated. The dispersion of droplets in the near-field immediately downstream of the splitter plate trailing edge where the turbulent mixing layer begins is accurately reproduced due to the realistic turbulent structures captured by the recycling/rescaling method

Ad-hoc boundary conditions for CFD analyses of turbomachinery problems with strong flow gradients at Farfield boundaries

This paper reports on the improvements of flux enforcement and auxiliary state farfield boundary conditions for Euler and Navier–Stokes computational fluid dynamics (CFD) codes. The new conditions are based on 1D characteristic data and also on the introduction in the boundary conditions of certain numerical features of the numerical scheme used for the interior of the domain. In the presence of strong streamwise gradients of the flow field at the farfield boundaries, the new conditions perform significantly better than their conventional counterparts in that they (a) preserve the order of the space-discretization and (b) greatly reduce the error in estimating integral output. A coarse-grid CFD analysis of the compressible flow field in an annular duct for which an analytical solution is available yields a mass flow error of 62% or 2%, depending on whether the best or the worst farfield boundary condition (BC) implementation is used. The presented BC enhancements can be applied to structured, unstructured, cell-centered, and cell-vertex solvers

Analysis of unsteady flows past horizonatal axis wind turbine airfoils based on harmonic balance compressible Navier-Stokes equations with low-speed preconditioning

This paper presents the numerical models underlying the implementation of a novel harmonic balance compressible Navier-Stokes solver with low-speed preconditioning for wind turbine unsteady aerodynamics. The numerical integration of the harmonic balance equations is based on a multigrid iteration, and, for the first time, a numerical instability associated with the use of such an explicit approach in this context is discussed and resolved. The harmonic balance solver with low-speed preconditioning is well suited for the analyses of several unsteady periodic low-speed flows, such as those encountered in horizontal axis wind turbines. The computational performance and the accuracy of the technology being developed are assessed by computing the flow field past two sections of a wind turbine blade in yawed wind with both the time-and frequency-domain solvers. Results highlight that the harmonic balance solver can compute these periodic flows more than 10 times faster than its time-domain counterpart, and with an accuracy comparable to that of the time-domain solver