Newsletter  2023.11  Index

Theme : "Mechanical Engineering Congress, 2023 Japan (MECJ-23)" Preface Hideo MORI, Tetsuya KANAGAWA Why do mistakes communicate and spread? (Diffusion and prevention of misperceptions regarding fluid mechanics) Ryozo ISHIWATA (Kanagawa Institute of Technology) Toward Digital Twin Numerical Turbine Satoru YAMAMOTO (Tohoku University) Measurements of turbulent wall pressure fluctuation field in a turbulent boundary layer and the wing-flat plate juncture flow using the many-channel microphone array Yoshitsugu NAKA (Meiji University) PSP and TSP for measuring pressure and temperature fields on wall surfaces and their applications Yasuhiro EGAMI (Aichi Institute of Technology) Flow measurement using MEMS differential pressure sensor Hidetoshi TAKAHASHI (Keio University), Takuto Kishimoto (Keio University), Kei Ohara (Keio University), Kyota Shimada (Keio University) Flexible Sheet Sensor for Advanced Flow Monitoring Masahiro MOTOSUKE (Tokyo University of Science)

 

Measurements of turbulent wall pressure fluctuation field in a turbulent boundary layer and the wing-flat plate juncture flow using the many-channel microphone array

Abstract

Yoshitsugu NAKA Meiji University

Many-channel microphone array has been developed for turbulent wall pressure fluctuation measurements. The microphone array consists of custom-made PCB boards with digital MEMS microphones shown in Fig. 1 and an FPGA signal controller. The digital data stream from the microphone is bundled and recorded. The pressure signals are recovered using a decimation sinc2 filter in the post-processing. The measurements have been performed in a turbulent boundary layer and in a wing–flat plate juncture flow. For the turbulent boundary layer, the instantaneous space-time distribution of the wall pressure fields shown in Fig.2 exhibits negative and positive wall pressure with packets of strong intermittent fluctuations. Statistical evaluations have been made: comparison of the rms values, the probability density function, and the power spectra. For the wing–flat plate juncture flow, the wall pressure fluctuations at 672 points on the flat plate and the velocity field in the stagnation plane have been measured simultaneously. The distribution of the RMS values of the wall pressure fluctuation shown in Fig. 3 indicates the trace of the strong wall pressure fluctuations. The relation between the wall normal velocity and the wall pressure fluctuations is quantitatively evaluated with the proper orthogonal decomposition (POD) analyses. Figure 4 indicates the POD modes of the wall normal velocity fluctuations having a significant correlation with the wall pressure fluctuations. Highly correlated POD modes indicate that the size of the turbulence structure is 0.2c, which can be associated with the wall pressure fluctuation near the wing on the stagnation line. It is demonstrated that the proposed microphone array can capture the wall pressure field that represents the turbulent flow characteristics.

Key words

Wall pressure fluctuations, Microphone array, Turbulent boundary layer, Flat plate-wing juncture flows

Figures

Fig. 1  A 56ch MEMS microphone array.

Fig. 2  Instantaneous space-time distribution of the wall pressure fluctuations in a turbulent boundary layer.

Fig. 3  Distribution of the RMS values of the pressure fluctuations on the flat plate in the wing-flat plate juncture flow. The color is normalized by the dynamic pressure .

Fig. 4  Shapes of the principal POD modes of the wall normal velocity fluctuations having a significant correlation with the wall normal velocity fluctuations.