Factors Influencing Computational Predictability of Aerodynamic Losses in a Turbine Nozzle Guide Vane Flow

Abstract

This paper deals with the computational predictability of aerodynamic losses in a turbine nozzle guide vane (NGV) flow. The paper shows that three-dimensional (3D) computations of Reynolds-Averaged Navier Stokes (RANS) equations have the ability to adequately represent viscous losses in the presence of laminar flows, transitional regions, and fully turbulent flow areas in the NGV of an high pressure (HP) turbine stage. The Axial Flow Turbine Research Facility (AFTRF) used for the present experimental results has an annular NGV assembly and a 29-bladed HP turbine rotor spinning at 1330 rpm. The NGV inlet and exit Reynolds numbers based on midspan axial chord are around 300,000 and 900,000, respectively. A general purpose finite-volume 3D flow solver with a shear stress transport (SST) k–ω turbulence model is employed. The current computational study benefits from these carefully executed aerodynamic experiments in the NGV of the AFTRF. The grid independence study is performed with static pressure coefficient distribution at the midspan of the vane and the total pressure coefficient at the NGV exit. The effect of grid structure on aerodynamic loss generation is emphasized. The flow transition effect and the influence of corner fillets at the vane–endwall junction are also studied. The velocity distributions and the total pressure coefficient at the NGV exit plane are in very good agreement with the experimental data. This validation study shows that the effect of future geometrical modifications on the turbine endwall surfaces will be predicted reasonably accurately. The current study also indicates that an accurately defined turbine stage geometry, a properly prepared block-structured/body-fitted grid, a state-of-the-art transitional flow implementation, inclusion of fillets, and realistic boundary conditions coming from high-resolution turbine experiments are all essential ingredients of a successful turbine NGV aerodynamic loss quantification via computations. This validation study forms the basis for the successful future generation of nonaxisymmetric endwall surface modifications in AFTRF research efforts.

A simultaneous use of a leading-edge fillet and a non-axisymmetrically contoured endwall in a turbine stage

“…Based on the discussion and the results presented by the authors in [31] and [32], a structured mesh to represent the flow field was applied. The three-dimensional computational mesh was created by GridPro, which is capable of generating a multi-block, body-fitted structured grid.…”

Statistical and Computational Evaluation of Axial Loss Correlations Applied to Centrifugal Turbines

“…The grid type and quality ratings could solely rely on some theoretical groundwork and few guidelines based on past experience. From a practical standpoint and by comparison to other existing grid varieties, hexahedral grids produce results of better numerical accuracy for RANS simulations of turbine flows [66] and have thus been adopted in this framework. Semi-automatic grid generation has been conducted by means of AutoGrid5 TM .…”

Unsteady Flow Structures within a Turbine Rim Seal Cavity in the Presence of Purge Flow—An Experimental and Computational Unsteady Aerodynamics Investigation

“…The solver was distributed in parallel mode with as many as 48 licenses used at a time. A comprehensive assessment and validity of the current computational infrastructure and the computer program was reported in a comprehensive report by Turgut and Camci [21]. Although a direct uncertainty analysis on the computed quantities were not reported, the computational results were compared against carefully measured aerodynamic NGV and rotor quantities.…”