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چكيده انگليسي :

Numerical study of blade coolings on gas turbine Behnam Abbasi b abbasi@me iut ac ir Date of Submission 2011 Department of mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Ahmadreza Azimian azimian@cc iut ac irAbstractGas turbines are widely used in industry The turbine inlet temperature of modern gas turbine engines has beenincreased to achieve higher thermal efficiency However the increased inlet temperature can result in materialfailure of the turbine system due to the higher heat transfer and induced thermal stresses In order to overcomethe potential problem from the high temperature environment and prevent failure of turbine components filmcooling has been widely employed as an active cooling method In a film cooled component relatively coolerair is injected through several discrete holes which form a protective film between the hot mainstream gas andthe turbine component to maintain the surface at a lower temperature thus protecting the turbine componentfrom failure The blade edge regions including the blade tip the leading edge and the platform are exposed tothe most extreme heat loads and therefore must be adequately cooled to maintain safety The leading edge ofthe rotor blade experiences the highest values of heat transfer coefficient That s why the most conventionalresearches including the present research places film cooling holes on leading edge of blade The cooling holeshave been made at three parallel rows The Gambit grid generation software was used to generate unstructuredgrids with fine grid clustering near the wall Computations have been followed upon the heat transfercoefficient of blades by Fluent to solve compressible Reynolds Averaged Navier Stokes equations This stephas been performed using the finite volume method to discrete the equations The turbulent equations are veryimportant because of complexity and turbulency within the flows in turbomachines At first to choose the mostproper model several turbulent models have been used from The models such as k k and derivativemodels from there and v2f model can be mentioned for this step The results have been compared withexperimental evidences In compare with experimental data Heat transfer coefficient shows a good agreementon pressure surface while the results on suction surface don t seem satisfactory The reason for this pooragreement could be placed on decreasing of pressure at suction surface that lead to instability of flow Bestpredictions have been made by k SST model and v2f model Because of expense matters the model of v2f hasbeen abandoned at this work Most researches on this subject are placed at stationary status while presuminghigh velocities for turbine blades The ignorance of blade motion can be justified by this notion At First blades film cooling has been studied without motion Then the effects of mass and temperature coolant have beenfollowed Secondly rotary blades have been studied for the variations of mass coolant at three velocities Temperature reduction of coolant doesn t have a great effect on heat transfer coefficient but decreases the heattransfer coefficient in small areas on the blades pressure surface Increasing mass coolant up to 1 percent of hotfluid decreases heat transfer coefficient at most area especially at pressure surface Also growth of mass coolantup to 1 5 percent of hot fluid increases heat transfer coefficient at some areas of suction surface near the leadingedge which is because of expansion in turbulency near the holes Variant of mass coolant has been studied withthree flows at rotator status Decreasing Heat transfer coefficient have caused raising mass coolant up to 1 5percent of hot gas Variations of mass coolant have been studied with three kinds of flows concerning rotatorstatus First of all under low and moderate velocities increasing mass coolant up to 1 5 percent causes areduction on heat transfer coefficient Second of all concerning high

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