Speed Water Tunnel Research Articles

Vibration and damping analysis of flexible aluminum tube under the variation of support plate geometry using low speed water tunnel

Vibration response and damping effects on flexible aluminum tube placed in tube-bundle under fluid interaction velocity of 0.5 m/s using water tunnel, is analyzed experimentally for drag and lift direction. The study is undertaken to reduce the flow-induced instabilities in heat-exchanger, proposing low-vibrating design approach. Therefore, three tube bundles in triangular arrangement using distinct support plate thickness of 2 mm, 2.8 mm, and 3.6 mm under (P/D) ratio of 1.45 are developed, respectively. The vibrations are sensed through tri-axial accelerometer mounted at top of central-tube. The damping factors are assessed for monitored/central tube of each tube-bundle at tuned natural frequencies of 9, 8, 7, and 6 Hz, respectively. Whereas, tube-vibration response is further analyzed in terms of RMS-acceleration and dimensionless magnitude at fixed natural frequency of 8 Hz. The results highlight that, the damping factors (under all four natural frequencies) exhibit increasing and the tube-vibrations show decreasing trend with increase in support plate thickness, respectively. Moreover, successive decrease in natural frequency of tube (9-6 Hz) influence the damping factors to increase for each tube bundle. Based on assessment, it is noted that tube-bundle comprising 3.6 mm thick support plate along 8 Hz natural frequency, shows maximum stability for given setup.

Design of a bubble collecting section in a high speed water tunnel for ventilated supercavitation experiments

The main objective of the present study is to design a bubble collecting section for use in ventilated supercavitation experiments. The large amounts of air ventilated around a cavitator split into small bubbles that follow the water’s passage through the water tunnel. The presence of these bubbles in the test section of the water tunnel prevents effective observation of supercavitation. To enable the clear observation of cavitation shape, a bubble collecting section with large volume is necessary upstream of the test section to collect bubbles. The buoyancy of bubbles provides a simple means for their collection. However, the bubbly flows in such systems have rather high velocities and a non-uniform velocity distribution, which degrades the buoyancy effect. In the present study, a bubble collecting section with three porous plates that produce a uniformly low velocity distribution is designed and analyzed with numerical methods. The effectiveness of this approach is assessed experimentally with the 1/10 miniature model. The reduction of the void fraction downstream of the bubble collecting section was also assessed in the test section. The bubble collecting section in the full-scale water tunnel was also eventually found to be well designed through flow speed measurements and bubble visualization in the test section.

S0503-1-3 十字交差円柱/平板系の縦渦励振を利用したマイクロ発電([S0503-1]自然の流体エネルギー利用技術(1))

The target of this research is to develop a micro electric power generator for a low cost small river monitoring device. The power generator extracts an energy from flow of the river through the trailing vortex induced vibration (TVIV) occurred on a cruciform circular cylinder/strip-plate system. A prototype model for water flow was made and tested in high speed water tunnel. It was confirmed that TVIV occurs in water flow from 0.5 to 4 m/s. Power generation experiments were carried out in the water tunnel and the electric power was obtained in the same velocity range. The experiments show that this micro electric power generator is appropriate for a natural river of which flow velocity changes greatly. The power generator affects on TVIV as a damper. The obtained electric power was almost the same as a energy which was estimated from energy balance analysis, assuming the power generator is damper.

Experimental Studies of Coaxial Jet Flows

An experimental study was carried out to investigate the effect of coaxial nozzle operating conditions on near-field jet plume development. The study was conducted in a low speed water tunnel as well as in a high-speed airflow nozzle test facility. Laser Doppler Anemometry (LDA) and Laser Induced Fluorescence (LIF) techniques were employed to identify the flow structure as well as the mean velocity and turbulence structure of a coaxial nozzle under low speed flow conditions. Schlieren flow visualization, LDA and nozzle wall static pressure measurement surveys were performed in high speed flows. The effect of a nozzle shroud on jet development was studied and found very effective on suppression of the shock cells and on reduction of turbulence levels within the core region. The effect of the outer and inner Nozzle Pressure Ratios on shock cell structure and the nozzle internal wall pressure field were documented. LDA measurements in the water tunnel confirmed that the flow pattern produced of the Reynolds numbers and velocity ratios selected for this study was typical of practically occurring developing jet flow fields. Sufficient measured profiles of velocities, turbulence quantities and nozzle wall static pressures as well as jet plume images have been captured to serve as benchmark validation data for time-averaged turbulence-model-based RANS CFD predictions.

Streamwise Distribution of the Skin Friction Reduction by Microbubbles

Local Skin friction reduction with microbubbles was measured in a two dimensional channel flow. Microbubbles are expected to reduce the skin friction which takes up a large part of the total ship drag. To adapt the process to a real ship is difficult because of the very large amount of microbubbles. In order to adapt the process to a real ship, we must search for more effective bubble conditions and the persistence of the effectiveness in streamwise direction.The local skin friction reduction was measured in the small high speed water tunnel, systematically changing the averages of void ratio, the main flow velocity and the measurement position from the bubble injection point. The results confirmed the persistence of the effect at the 200δ point (boundary layer thickness) downstream air injection. The local void ratio and the velocity profile using the PIV system were measured. The measurements indicated that the local void ratio near the wall was important to the skin friction reduction.

134 マイクロバブルを含む流れのPIV計測

Skin friction reduction devices for ships have been studied, but a reliable device has not been found. The authors are experimentally investigating one of the devices, which is Microbubbles. The microbubble-is a more effective device for reduction of local skin friction, but the reduction mechanism is not made clear.We successed in visualizing the microbubbles in a boundary layer of a high speed flow, U=10m/s, in a small high speed water tunnel using PIV and two YAG lasers system. The shape and the distribution of microbubbles in a boundary layer are found by photography. Next target is to measure the velocity distribution with microbubbles in a boundary layer.

Control of natural laminar instability waves on an axisymmetric body

Abstract : An experimental investigation of the control of natural laminar instability waves on an axisymmetric body was conducted in the NOSC high speed water tunnel. The body was a 9:1 ellipsoid of revolution, 50mm in diameter at the midsection. Control perturbations were introduced into the boundary layer through a suction/blowing slot of 0.075mm width at 130mm from the nose. Hot film sensors before and after the slot were used to measure the passage and attenuation of the instability waves. A very simple invert and delay control loop was used to control a speaker embedded in the suction/blowing slot. At a freestream velocity of 8.67m/sec, and approximately 50 percent reduction in the RMS fluctuations of the instability waves was achieved after control. At this velocity the frequency of the instability waves was about 1kHz. The experimental run conditions corresponded to Reynolds numbers, at the slot location, of 1.24 million and 1520 based on axial location and boundary layer displacement thickness respectively. Torpedo systems, Subsystems, Components, Propellers.

The high speed water tunnel facility at the Indian Institute of Science

The present article about the high speed water tunnel facility at the Indian Institute of Science, Bangalore, provides a general description of the tunnel circuit, and brief reports on the performance of the facility and some typical results from investigations carried out in it. A unique aspect of the facility is that it has a horizontal resorber in the form of a large cylindrical tank located in the lower leg of the circuit. The facility has been used, among other things, for flow visualization studies, and investigations on marine propeller hydrodynamics and “synthetic cavitation”. The last topic has been primarily developed at the Indian Institute of Science and shows considerable promise for basic work in cavitation inception and noise.

A Comparison of Two Optical Techniques for Measuring Cavitation Nuclei

Several devices have been developed or adapted to the use of measuring “nucleating sources” in a liquid including acoustic methods, direct observation (e.g. microscopy and holography), single particle counters, light scattering and light extinction. With experience two techniques have become more favored than the others, namely: holography and light scattering. However, with the exception of Peterson et al’s study no attempt has been made to simultaneously compare these two techniques under actual test conditions so that some confidence may be gained in deducing the number and type of nuclei from the record produced by either method. The purpose of the present paper is then to report and compare some nuclei populations which were recorded simultaneously by both methods during a series of cavitation inception tests. Measurements of nuclei populations were made in two facilities located at the California Institute of Technology, the Low Turbulence Water Tunnel (LTWT) and the High Speed Water Tunnel (HSWT) which are known to have substantially different nuclei distributions. In each facility nuclei populations were recorded at various combinations of tunnel velocity, pressure and pressure-time histories in an effort to produce different distributions and also to enable one to deduce from the laser scattering results the composition of the nuclei, i.e., solid particulates or bubbles. This deduction could then be checked with the holographic results. Simultaneous nuclei population measurements were recorded in the LTWT, whereas measurements of nuclei in the HSWT were obtained at separate times approximately eleven months apart. Since both methods have different characteristic size detection ranges, they could be compared directly only in the overlapping size range, namely: 10-50 microns diameter. In the LTWT where the populations were recorded simultaneously, there was some good agreement between not only the numbers but also the type of nuclei (mainly gas bubbles). However, the scattering technique indicated somewhat fewer nuclei in most cases. In addition, the scattering technique indicated fewer nuclei in the HSWT than had been previously measured by holography. Although there was some discrepancy between numbers of nuclei, both techniques demonstrated (directly from holography and by inference from the scattering results) that the nuclei were primarily solid particulates rather than gas bubbles.

Cavitation on hemispherical nosed teflon bodies1

In a high speed water tunnel, incipient and desinent cavitation are investigated on a series of hemispherical nosed teflon bodies. The results are compared with those measured previously on a series of stainless steel bodies. The experiments cover a

Water Tunnel Techniques for Force Measurements on Cavitating Hydrofoils

The paper reviews briefly experimental techniques and data-correction procedures developed in connection with studies in the High Speed Water Tunnel, California Institute of Technology, for hydrofoil force measurements. The matters discussed relate chiefly to problems of force measurement in cavitating flow and to procedures devised to solve them. Items considered in this connection are water-tunnel balances, the effects of tip-clearance flows, tare corrections, the importance of cavity-pressure measurements, cavitation scaling, tunnel-wall effects, and hydroelastic effects.

Proposed Acoustic System for Ordnance Research Laboratory Water Tunnel

A description is given of the acoustic methods and equipment for detecting and locating sources of cavitation on underwater bodies and propellers (under test) in the high speed water tunnel now under construction at the Ordnance Research Laboratory at the Pennsylvania State College. Sound arising inside the tunnel will pass through an acoustically transparent window to an external tank in which is placed a small piezoelectric crystal hydrophone at the focus of an ellipsoidal reflector. The source of sound can thus be located because the hydrophone is most sensitive to sounds originating at the conjugate focus of the ellipsoid which is inside the tunnel. The reflector and hydrophone assembly has three degrees of freedom.