A Computational Methodology for Large-Eddy Simulation of Tip-Clearance Flows

Abstract

A large-eddy simulation (LES) solver which combines an immersed-boundary technique with a curvilinear structured grid has been developed to study the temporal and spatial dynamics of an incompressible rotor tip-clearance flow. The overall objective of these simulations is to determine the underlying mechanisms for low-pressure fluctuations downstream of the rotor near the endwall. Salient features of the numerical methodology, including the mesh topology, the immersed boundary method, the treatment of numerical instability for non-dissipative schemes on highly skewed meshes, and the parallelization of the code for shared memory platforms are discussed. The computational approach is shown to be capable of capturing the evolution of the highly complicated flowfield characterized by the interaction of distinct blade-associated vortical structures with the turbulent endwall boundary layer. Simulation results are compared with experiments and qualitative as well as quantitative agreement is observed.

Large-eddy simulations in mixed-flow pumps using an immersed-boundary method

“…As of today very few applications of immersed-boundary methods to such flows can be found in the literature and usually deal with simplified configurations (see for example [30,31]). The aim of the present work is to explore the feasibility of utilizing such an approach in the case of turbopumps, where the complete machine is simulated.…”

“…As of today very few applications can be found in the literature, which usually deal with simplified configurations. You et al [30,31], for example, performed LES using an immersed-boundary method and a structured generalized curvilinear coordinate solver, to study the viscous losses associated to the tip-clearance flow in a linear cascade. To reduce the cost of the computations a single vane was considered, using periodic boundary conditions.…”

Comparative study of large eddy simulation of film cooling using a dynamic global-coefficient subgrid scale eddy-viscosity model with RANS and Smagorinsky Modeling

“…These shortcomings of the Smagorinsky model were overcome by Germano et al [27] through a dynamic procedure for determining the model coefficient. The shortcoming of dynamic procedure proposed by Germano et al is numerical instability since its value often becomes negative and/or highly fluctuates in space and time which needs additional numerical procedures [28][29][30][31]. Vreman [32] developed a new subgrid-scale eddy-viscosity model.…”

Experimental investigation on unsteady pressure fluctuation of rotor tip region in high pressure stage of a vaneless counter-rotating turbine

“…In modern high load turbines, the loss induced by tip clearance leakage flow is remarkable. A number of investigations on tip clearance leakage flow have been performed by many researchers [9][10][11][12][13][14][15][16][17][18][19][20][21][22] to decrease the flow loss. Farokhi [9] analyzed the tip clearance loss in an axial flow turbine and proposed a model that accounts for tip pressure loading, relative wall motion and stage characteristics.…”

“…The structure of the aerothermal losses in the passage changed dramatically when the outer casing motion was incorporated, but the total losses in the passage remained very similar. You et al [18] carried out a study on the temporal and spatial dynamics of an incompressible rotor tip clearance flow by means of a large-eddy-simulation-based flow solver. The computational approach was shown to be capable of capturing the evolution of the highly complicated flow field characterized by the interaction of distinct blade-associated vortical structures with the turbulent end-wall boundary layer.…”