Universality in small scale structures in pressure fluctuation in turbulence

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In this study we report on the experimental result of pressure statistics measured in the free jet in the range of Reynolds number ; 200 【less than or equal】 R_λ 【less than or equal】 1200. And the traditional theories for the scaling properties of pressure statistics. Which are not yet confirmed in a number of important aspect, are checked. The measurement of pressure fluctuation in the flow field was accomplished with standard quarter-inch condenser microphone and the small transducer, respectively. They were fitted with a tubing as a pressure duct and were inserted into the flow domain in such a way that the axis of the microphone (or the transducer) body was aligned with the mean stream. The static tube is 1mm in diameter and 15mm in length which has four static holes (0.4mm in diameter) on the surface. The frequency response of the microphone with the necessary ancillary equipment is flat up to 15kHz. But the lower frequency can be measured down to 20Hz. This is not enough for high Reynolds number flow or the flow in which the large scale motions are contained. So we adopted the small transducer in the case of 300 【less than or equal】 R_λ. There seems to be no agreement about the scaling of pressure spectrum when compared to the case of energy spectrum. The present experiment shows that the clear -7/3 power-law was confirmed for 650 【less than or equal】 R_λ. This is significantly higher Reynolds number than those needed for inertial scaling in velocity statistics. Smaller than this Reynolds number, but R_λ 【greater than or equal】 350, the spectral exponent departs from -7/3. The coefficient C_p is not universal but depends on the Reynolds number. If we approximate the relation by the linear fit in log-log coordinate, it is C_p ∝ R_λ^<1.3>. We think these results are rally new experimental results.