LDV and PIV Measurements of the Organized Oscillations of Turbulent Flow over a Rectangular Cavity

• Published in: Journal of Fluid Science and Technology Vol. 5; no. 3; pp. 370 - 383
• Main Authors: MORI, Takayuki, NAGANUMA, Kenji
• Format: Journal Article
• Language: English
• Published: Tokyo The Japan Society of Mechanical Engineers 2010; Japan Science and Technology Agency
• Subjects: Cavity Oscillation; Turbulent Flow
• ISSN: 1880-5558; 1880-5558
• DOI: 10.1299/jfst.5.370

This paper presents results of an experimental study of the organized oscillation of incompressible turbulent flow over a rectangular cavity. Experiments were carried out to clarify the oscillation frequencies and the strength of shear layer-cavity trailing edge interaction. LDV and PIV measurements were made in a closed re-circulating water tunnel for rectangular cavities with L/D (L; cavity length, D; cavity depth) =2 and L/D=4. Measurements were also made for a backward facing step flow. Reynolds number based on momentum thickness was 8,300. LDV-measured velocity spectra reveal that self-sustained oscillations due to shear layer-trailing edge interaction are absent or very weak. At the upstream part of the cavity, dominant frequencies of the velocity fluctuations show little variation with L/D, and the frequencies are close to those of the shear layer instability. As the measuring point moves to the downstream, oscillation frequencies decrease and the peaks of the spectra become unclear. PIV-measured instantaneous flow fields show the existence of organized vortical structures in the cavity shear layer. From PIV images, frequencies of cavity oscillation are visually estimated and the results are compared to the LDV-measured velocity spectra.