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.
Optimization of pre-swirl nozzle shape and radial location to increase discharge coefficient and temperature drop
Hole-type pre-swirl nozzle was optimized using CFD analysis and experiments. CFD methodologies were validated by comparing the CFD results with experiments. Four design variables were considered in the optimization process: Nozzle inlet length (L), outlet length (l), inlet diameter (D), and radial location (rp). The optimization process included the optimal Latin hypercube design sampling method with the Kriging surrogate model and genetic algorithm. The single-objective optimization was performed to maximize the discharge coefficient. Results showed that the optimized nozzle reduced total pressure losses and increased mass flow rate. Total temperature drop effectiveness was increased from 0.07 to 0.29. The total temperature in pre-swirl system could be characterized as the reduction in temperature by nozzle acceleration and elevation by aerodynamic losses due to friction and viscous effects in the system. The optimized model showed a discharge coefficient of 0.846, which was 31.7 % higher than the baseline condition. By improving the discharge coefficient the pre-swirl system reduced aerodynamic losses, and the mass flow rate was increased at certain pressure ratios or satisfied the pressure margin for blade cooling.
Numerical Simulation of a Simulated Film Cooled Turbine Blade Leading Edge Including Conjugate Heat Transfer Effects
A conjugate numerical method was used to predict the normalized “metal” temperature of a simulated turbine blade leading edge. This computational study was done in conjunction with a parallel effort to experimentally determine normalized metal temperature, i.e. overall effectiveness, using a specially designed model blade leading edge. Also examined in this study were adiabatic models which provided adiabatic effectiveness results. Two different film cooling configurations were employed. The first configuration consisted of one row of holes centered on the stagnation line. The second configuration had two additional rows located at ±25 degrees from the stagnation line. These simulations were run at two different blowing ratios, M = 1 and M = 2. The coolant to mainstream density ratio was 1.5. The computational simulation was conducted using the FLUENT code using the realizable k-e turbulence model and with grid resolution within the viscous sublayer. Adiabatic effectiveness distributions were predicted well by the computational simulations, except for localized areas near the holes. Predictions of overall effectiveness were higher than experimentally measured values in the stagnation region, but lower along downstream section of the leading edge. Reasons for the differences between computational predictions and experimental measurements were examined.Copyright © 2009 by ASME