Flow analysis of combined impingement and film cooled gas turbine nozzle guide vane
In the present study, a typical nozzle guide vane (NGV) is considered with twenty six rows of impingement holes combined with thirteen rows of film cooled rows for the flow analysis. The coolant mass flow variations in different rows of the film holes externally subjected to the hot main stream are obtained by making a three dimensional computational analysis of NGV. The analysis is performed with the help of Fluent software. Attempts were made to study the effect of two parameters: (i) inlet coolant mass flow rate and (ii) external flow Reynolds number for a typically cooled NGV. Detailed coolant flow mass flow rate, pressure drop and temperature distributions are presented with an array of multiple jets impinging on a gas turbine high pressure NGV with a staggered array of film cooled rows. Results are presented for three laboratory test cases by varying flow rates for FIT and AIT. Coolant flow rate values at each row of film hole are compared among these test cases. The each row of a film hole is noticed with coolant mass flow rate, pressure drop and temperature rise across the hole found to increase with increase of coolant supply conditions at the two plenums. Owing to the interaction between hot main stream and the coolant that effuses out of the film holes, occasional presence of hot gas ingestion is noticed for certain flow rates. This causes nonlinear distribution in mass flow, pressure drop and temperature rise. These behaviors suggest a possibility of locally optimized solutions for a combination of coolant mass flow and mainstream Reynolds number.
Coupled flow network model and CFD analysis for a combined impingement and film cooled gas turbine nozzle guide vane
The nozzle guide vane (NGV) of a gas turbine engine possesses complex cooling passages, with inherent thermo-fluid dynamic interactions between the vane and the main stream. The present paper is an attempt to make use of the Computational Fluid Dynamics(CFD) tools as well as the flow network analysis tools, in combination, for analyzing typical cooled NGV flow passages. CFD results containing the static and total pressure contours are presented in the paper and are summarized as simple correlating relations; these in turn are used to generate the discharge coefficients as input to the flow network. The pressure conditions at different boundary nodes are further input to the flow network analysis. The mass flow rate and pressure drop values through the impingement and film holes are obtained as output from the flow network model. Comparison of the results from one-dimensional approach coupled with threedimensional CFD analysis with the available literature by Jin et al. [7] shows a good agreement for the operating pressure ratio in the range of 1.2 to 1.5 at pressure surface rows of the film cooling holes in the leading edge region of the vane. The accuracy of the calculated total pressure ratio on the pressure surface rows of the leading edge circuit has been found satisfactory.The coolant from FIT and AIT are 25.5% and 74.5% respectively. The secondary fluid flows from FIT is 24.3% fed to the leading edge film holes, while 51.9% of coolant is fed to the mid-chord region through the film holes, 22.5% coolant flows out of the trailing edge film holes and the remaining 1.3% flows through trailing edge slot
Heat Transfer for a Turbine Blade With Nonaxisymmetric Endwall Contouring vortical secondary flows that are present near the endwall of an axial gas
turbine blade are responsible for high heat transfer rates and high aerodynamic losses. The application of nonaxisymmetric, three-dimensional contouring to the endwall surface has been shown to reduce the strength of the vortical flows and decrease total pressure losses when compared with a flat endwall. The reduction in secondary flow strength with nonaxisymmetric contouring might also be expected to reduce endwall heat transfer. In this study, measurements of endwall heat transfer were taken for a low-pressure turbine blade geometry with both flat and three-dimensional contoured endwalls. Endwall oil flow visualization indicated a reduction in the passage vortex strength for the contoured endwall geometry. Heat transfer levels were reduced by 20% in regions of high heat transfer with the contoured endwall, as compared with the flat endwall. The heat transfer benefit of the endwall contour was not affected by changes in the cascade Reynolds number. DOI: 10.1115/1.4000542 A fundamental issue in the design of gas turbine engines is the detrimental effects of vortical flows that are present near the junction of the airfoil and its endwall. These flows, generally termed secondary flows, increase aerodynamic losses through the turbine leading to lower overall engine efficiency. Furthermore, the vortical flows result in high heat transfer rates due to mean flow distortion and high turbulence levels. For highly loaded parts such as the low-pressure turbine blade in this study, part durability can be significantly impacted by high heat transfer. It is obvious that reducing or eliminating the effects of the secondary flows would result in appreciable benefits in an engine, and thus, much research has been conducted to understand these flows and control them. Past research has shown that three-dimensional modifications to the endwall surface, generally referred to as nonaxisymmetric contouring, are an effective method of reducing or eliminating secondary flows. The peaks and valleys in the endwall locally decrease or increase the static pressure, respectively, which can reduce the pressure gradient between adjacent airfoils that strengthens secondary flows. Weaker secondary flows result in lower aerodynamic losses, as has been documented by many researchers. However, few studies have considered the effect of nonaxisymmetric contouring on endwall heat transfer, and thus, the overall benefit of contouring in an engine is not completely understood as of yet. This paper discusses the effect of nonaxisymmetric contouring on the endwall heat transfer for a low-pressure turbine blade. The effect of varying the cascade Reynolds number for both the flat and contoured endwalls is also considered.