Comparison of the performance of cobra probe and hotwire in circular cylinder wake

The performance of cobra probe and hotwire is compared in a circular cylinder wake at the Reynolds number of 7200,including time-averaged velocity,Reynolds stresses,probability density functions,auto-correlation coefficients and spectra.Based on the experimental results,it is found that the rejection rate of cobra probe increases with turbulence intensity.However,its effect on the time-averaged results is negligibly small.Although the acceptability rate of cobra probe is higher than 95%,it over estimates the Reynolds stresses compared to hotwire.Particu-larly,for the main Reynolds shear stress u*v*,the difference of measurements between cobra probe and hotwire is significantly larger than those for the Reynolds normal stresses.Since cobra probe can not capture high frequency fluctuation,the auto-correlation coefficients of velocities present stronger periodicity relative to that of hotwire.The responses of cobra probe are different for u and v,resulting in significant difference in their spectra in the inertial sub-range,and thus it can not reveal the local isotropy of small scale turbulence in the inertial sub-range.