شبيه سازي و بررسي سه بعدي اثر زبري سطح روي پديده هاي سرج و استال بر روي يك مرحله كمپرسور محوري

چكيده انگليسي :

72Three Dimensional Simulation and Investigation of Surface RoughnessEffects on Surge and Stall Margins in One Axial Compressor Amir Bagherzadeh a bagherzadeh@me iut ac ir Date of Submission 2015 07 06 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Ahmad Sedaghat Sedaghat@cc iut ac irAbstract Aerodynamic instabilities are one of the most important issues for compressor designers Manyexperimental works have already studied these instabilities that occur around the maximum of the total to total pressure ratio However the basic mechanisms of these flow phenomena are not yet fully understood Usually the first instability encountered in most compressors is rotating stall that is characterized by one ormore cells of stalled flow that rotate at a fraction of the rotor speed This instability is usually responsible fora performance reduction efficiency pressure ratio etc and large vibrations that reduce the blade lifeduration Moreover it can induce surge a low frequency instability that leads to a mechanical failure of thewhole system In order to avoid such instabilities designers usually apply a safety margin called the surgemargin Unfortunately this strong constraint limits the efficiency and leads to an over dimensioning of thecompression system The possibility to reduce the surge margin is thus of a great interest for designers However operation closer to the stability limit increases the probability of stall inception The lossesaccompanied with instabilities decrease life duration and performance of compressors It is anticipated thatsurface roughness may reduce compressor performance although it may enhance surge characteristics ofcompressor stages Surface roughness increases significantly due to erosion corrosion and deposition duringoperation under high pressure and temperature condition and even exists on new made blades The increasedsurface roughness of compressor passage walls limits airflow and leads to flow loss However the partialincrease of roughness may also restrain flow separation and reduce flow loss It is necessary to exploremethods that will lower compressor deterioration thereby improving the overall performance In this paper one state of an axial compressor of a turbo shaft engine is computationally investigated Numerical resultsare obtained in three dimensions using a finite volume solver for incompressible RANS equations with SSTturbulence modeling Effects of surface roughness on performance and instabilities of the stage in differentrotational speeds have been explored In high rotational speeds from to increasingsurface roughness will improve the surge margin at the cost of lower efficiency of the stage however inlower rotational speed than there is an unexpected phenomenon of improving surge marginsimultaneously by increasing efficiency of the stage These results also show that the main effect ofinstability is to decrease flow rate hence to decrease the stage compression ratio Therefore differentcombination of uniform and non uniform surface roughness on rotor and stator blades was examined Computational results revealed that the rotor has contributed higher effects on the performance ofcompressor In particular the effects of roughness on pressure surface are higher than suction surfaces ofblades The effects of variable roughness on rotor blade surfaces in span wise direction were also examinedwhich show significant effects on work redistribution along rotor blades It has been found that for thefunctions with increasing values from root to tip aerodynamic performance and efficiency have betterconditions These may have important desirable effects on design of compressor stages with improved surgemargin and efficiency Keywords Axial compressor Surge Stall Surface roughness Efficiency Rotational speed

باقرزاده، امير

شبيه سازي و بررسي سه بعدي اثر زبري سطح روي پديده هاي سرج و استال بر روي يك مرحله كمپرسور محوري

استال , بازده , نسبت فشار , سرعت دوراني