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.
Heat Transfer Distribution of Semicylindrical Concave Surface Impinged by Circular Jet Rows
The impingement cooling of the leading edge of a gas turbine airfoil is modeled by considering impingement of three rows of jets on a semicylindrical concave surface. Experimental investigations are conducted to study the influence of jet-to-jet distance (s/d = 2.83, 4, and 6) and jet-to-plate distance (z/d = 2, 4, 6, and 8) on the local heat transfer of a semicylindrical concave surface impinged by three rows of multiple jets for different Reynolds numbers (12,000, 15,000, and 18,000). The local heat transfer coefficient is estimated using thermal images obtained by infrared thermal imaging technique. The local distribution of Nusselt numbers and the overall average Nusselt numbers were computed and compared. It was observed that the local heat transfer coefficients at 0 = 0° decrease with increase in z/d, whereas the heat transfer coefficients at θ = 60 and 80° increase with an increase in z/d at all Reynolds numbers. The configuration with s/d = 2.83 and z/d = 4 is observed to have the maximum heat transfer distribution with minimum coefficient of variance compared to other configurations at all Reynolds numbers covered in this study.
Conjugate Heat Transfer Analysis for Film Cooling Configurations With Different Hole Geometries
Secondary flows in the cooling jets are the main reason for the degradation of the cooling performance of a film-cooled blade. The formation of kidney vortices can significantly be reduced for shaped holes instead of cylindrical holes. For the determination of the film cooling heat transfer, the design of a turbine blade relies on the conventional determination of the adiabatic film cooling effectiveness and heat transfer conditions for test configurations. Thus, additional influences by the interaction of fluid flow and heat transfer and influences by additional convective heat transfer cannot be taken into account with sufficient accuracy. Within this paper, calculations of a film-cooled duct wall with application of the adiabatic and a conjugate heat transfer condition have been performed for different configurations with cylindrical and shaped holes. It can be shown that the application of the conjugate calculation method comprises the influence of heat transfer on the velocity field within the cooling film. In particular, the secondary flow velocities are affected by the local heat transfer, which varies significantly depending on the local position.Copyright © 2003 by ASME