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چكيده انگليسي :

Numerical Analysis of Inlet Boundary Condition Effects on Heat Transfer Simulation Results in a Gas Turbine Blade Mahdi Arezoomand m arezoomand@me iut ac ir April 19 2010 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiM Ashrafizadeh Email mahmud@cc iut ac irAbstractGas turbines are widely used in industry As the inlet gas temperature increases thermal efficiency andoutput power of the gas turbine increases However we should consider the maximum temperature limit forthe inlet burned gas due to metallurgic properties pertaining to the melting temperature of the blade In orderto investigate the cooling system implemented in the passing ways of the gas turbine it is necessary tosimulate the flow through turbine blades using appropriate softwares before starting with experiments A realnumerical simulation always requires complete information from turbine operating conditions which aregenerally unknown and expensive to acquire Therefore we have to make rational approximations of theoperating conditions enabling us to run some numerical simulation and assess the percentage of the variationin the results due to these approximations so that we will understand as to how much careful we shouldmove forward with the collection of the information First of all the heat transfer and turbulent flow field through the blades are solved using the a commercialCFD software in which the conjugate heat transfer method is implemented Numerical results obtainedthrough this endeavour are in good agreement with the experimental results which shows that the conjugateheat transfer is an efficient method for predicting flow pattern and heat transfer through gas turbine vanes After ensuring the accuracy of the simulation results the effect of reasonable estimation on boundaryconditions used in each boundary has been studied Results clearly indicate that by changing the turbulence length scale in a reasonable range at the inlet sectionof the main channel maximum variation of the predicted temperature does not exceed 0 6 By changing theturbulence intensity in a reasonable range at the inlet section of the main channel maximum variation of thepredicted temperature is about 1 8 By making reasonable suggestions for the inlet velocity profile maximum variation of the predicted temperature reaches about 3 8 If there is not enough informationabout the inlet velocity profile it is strongly recommended to use a profile similar to those of experimentaldata that is used in this study Using this profile could reduce maximum effects on the predicted temperatureto about 2 2 Results show that the type of curved profiles used for the inlet temperature causes only 0 7 variation on the temperature of the vane However the difference between the temperature of the vaneobtained using the uniform inlet temperature profile and the results of the curved profiles are considerable Close review of the results reveals the fact that the results of the curved profiles are in good agreement withindustrial observations Results show that by changing the turbulence intensity in a reasonable range at the inlet of the coolingsection maximum variation of the predicted temperature is less than 1 By changing the inlet velocityprofile of cooling channel between two extreme profiles maximum variation of the predicted temperaturereaches about 2 Results show that the effect of vane end wall cooling heat flux on the vane temperature isneglectable Obviously these conclusions are applicable to a specific vane and in general they only representthe scale of variation of the numerical results due to boundary conditions variations Key WordsGas Turbine Conjugate heat transfer Boundary sensitivity Cooling

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