This paper presents results of an experimental study on incompressible turbulent flow over a rectangular cavity. The experiment was carried out to clarify the strength and three-dimensional nature of cavity oscillations for fully turbulent inflow. Particle image velocimetry (PIV) and fluctuating pressure measurements were made in a closed, re-circulating water tunnel for cavity length-depth ratio from L/D=1 to 4 at a momentum thickness based Reynolds number, Re θ =8,300. Measured power spectra of pressure fluctuations show dominant frequencies with broad peak width indicating the absence of resonant oscillations. Pressure fluctuations at two spanwise separated locations are well correlated at the frequency range in which dominant peaks are found. Instantaneous flow fields reveal strong three-dimensional distortions. Although formation and passage of turbulent eddies are observed in the instantaneous x (streamwise)-y (vertical) plane flow field, instantaneous x-z (spanwise) plane flow fields show strong spanwise variations.

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.

Experimental study on tip vortex cavitation (TVC) was carried out for elliptical hydrofoils with various chord lengths. The purpose of the experiment was to clarify the influences of Reynolds number and water quality on tip vortex cavitation. Experiments were made in a large cavitation tunnel of the Naval Systems Research Center, TRDI/Ministry of Defense Japan. The elliptical hydrofoils tested were NACA 0012 cross section with chord lengths of 500mm, 250mm and 50mm. Reynolds number based on hydrofoil chord length was 2×105 < ReC < 7.4×106. Water quality of the tunnel was characterized by air content and nuclei distribution. Air content of the tunnel was varied between 30% and 80%. Nuclei distribution was measured by a cavitation susceptibility meter (CSM) with center-body venturi. Cavitation inception was determined from high speed video observation. A standard formula, (σL/σS) = (ReL/ReS)n, was applied for the scaling. In the present study, exponent of the scaling law n was found to be 0.2 < n < 0.4. High speed video observation showed that the process of the TVC inception strongly depends on water quality. In the experiments, unsteady behaviors of TVC were also investigated. Strong interactions between sheet cavitation and TVC were observed.

The Flow Noise Simulator (FNS) is a new large and quiet cavitation tunnel constructed by Naval Ship Systems Research Center of TRDI/Ministry of Defense, Japan for naval hydrodynamic and hydroacoustic research. This paper describes several results obtained from the initial evaluation tests of the facility involving, 1) flow uniformity and turbulent intensity at the test section, 2) LDV (Laser Doppler Velocimetry, 3) High Reynolds number turbulent boundary layer on the test section wall, 4) Acoustic noise source detection capability of the hydrophone array.

The Flow Noise Simulator (FNS) of the 1st Research Center of TRDI/JDA (Japan Defense Agency) is a large, variable pressure, recirculating water tunnel with very low background noise level. The tunnel is 20m high and 49m long, containing 2000m3 of water. The test section has a square cross section of 2m × 2m with 10m in length. It will accept large size surface ship models of 6m, submarine models of 4m in length and full scale ship appendix models. The FNS is currently under construction and will be accomplished in 2005. It will be used for a wide variety of hydrodynamic and hydroacoustic testing of surface ships and submarines, such as propeller cavitation noise measurements and propeller-hull interaction observation, with sufficiently large scale models. Conceptual design of the FNS was started in 1996 and evaluated by following scale model studies. This paper discusses some technical issues of the FNS.