Study on the influence of pneumatic probe on the wake flow field of transonic turbine cascade

The pneumatic probe is widely used for contact measurements in turbomachinery flow field research.However,it inevitably interferes with the original flow field,leading to additional errors,particularly in wake flow fields or transonic regions with significant pressure gradients.This study employed Reynolds-Averaged Navier-Stokes delete and high-fidelity numerical simulation to investigate the impact of an inserted pneumatic probe on the wake flow field of a transonic turbine blade and compared it to the baseline flow field.Results indicate that the probe causes the shock waves premature occurrence in the high subsonic wake region near the turbine blade trailing edge.These shock waves affect vortex shedding by thickening the boundary layer near the trailing edge and changing the shedding pattern from high-frequency-low-energy to low-frequencyhigh-energy.In addition,the extra flow loss is incurred,and the blade's heat transfer characteristic is changed.This research provides a reference for testing experiments in complex transonic flow fields,guiding experimental researchers to minimize instrument interference with the original flow field.

Shock Wave Spectrum Forming around the Compound Five-Hole Probe and its Influence on Pneumatic Parameters Acquisition during Subsonic to Supersonic Flow

Supersonic wind tunnel experiment is one of the important measurements for developing advanced gas turbines,and supersonic multi-hole probes are sophisticated tools to measure pneumatic parameters in such experiments.However,shock waves form around the probe head in supersonic flow,which affect the accuracy of results.In this study,a supersonic five-hole probe is selected as the research object.Firstly,a compound five-hole pressure-temperature probe was designed and produced with 3D-printing technology.Then,the shock wave spectrum was numerically calculated by three methods,which were the Mach number,density gradient,and shock function;in contrast to the other two methods,the shock function could accurately identify the types and ranges of shock and expansion waves.The results show that a strong shock wave is formed at the front section of the probe head,and the shock wave generated around the pressure measuring tube affects the total pressure and Mach number of the flow field,which causes the increase of entropy.The intensity of the shock wave at the head of the pressure measuring tube is the largest,causing a decrease in the total pressure around the flow field.Afterwards,to reduce the calculation errors caused by neglecting the compressibility of gases and the entropy increase,a gas compression factor δ_(s) was introduced.It is proved that the error of the calculated pneumatic parameters is less than 5% and 10% in subsonic and supersonic condition,respectively,with the gas compression factor considered.The research results of this paper provide theoretical reference for the design and use of pneumatic probes during subsonic to supersonic flow.