Takeyoshi Kimura

Hydrodynamic characteristics of a butterfly valve — Prediction of pressure loss characteristics

Abstract Investigation on fluidmechanic performance on a butterfly valve has been carried out. A practical valve model of a given thickness and a hub is used for the loss coefficient theory. A theoretical loss coefficient has been formulated from a contraction factor obtained by applying the generalized Borda mouthpiece theory. Cavitation stages (such as cavitation inception, supercavitation inception, cavitation damage inception, choking cavitation) have been theoretically predicted from the valve loss coefficient. The cavitation prediction has been carried out by applying the free streamline theory, where the relation between the loss coefficient and the critical cavitation factor has been formulated. The results of the theoretical prediction equations agree well with the experimental results.

Fluid dynamic effects of grooves on circular cylinder surface

It is shown that a groove on the surface of a circular cylinder affects movement of the separation point backward and reduces draw even at Reynolds numbers of about a few thousand. Several types of circular-arc cross-section grooves are studied using flow visualisations and numerical simulations. Whether these grooves are effective depends strongly on their positions, and the most effective positions are about 80 deg, measured from the foremost point. When they are effective, cavity flows are developed inside the grooves. This effect corresponds to that of dimples on golf balls and will explain unique characteristics of the drag curve.

Hydrodynamic characteristics of a butterfly valve — Prediction of torque characteristics

Abstract This study has focused on the prediction of torque characteristics of butterfly valves and we propose a prediction equation derived from theoretical investigation and experimental results. The free-streamline theory is applied to the prediction of the torque characteristics because the flow separation was confirmed on the rear surface by flow visualization. Actual valves are affected by the duct wall. These effects are considered as the change of attack angles and approaching velocities of the flows. Thus, the correction for these effects is added to the theoretical torque equation obtained by the free-streamline theory. The results of our prediction are shown to be successful comparing with the experimental results.

Wake of a rotating circular cylinder

Flow about a rotating circular cylinder is one of the classical problems of fluid mechanics. The Karman vortex street in the wake of a still circular cylinder is one of the most well-known phenomena in fluid mechanics. It is of interest how the vortex street is affected by the rotation of the cylinder. It is so far known by experiments that the Strouhal number of vortex shedding becomes larger as the rotating speed becomes higher and that the meandering of the wake due to the Karman vortex street disappears when the rotating speed of the cylinder is high enough, that is, when the spin parameter, which is defined as the ratio of the peripheral speed of the cylinder surface of the uniform velocity, is about 2. The Reynolds number in which these experiments have been done is of order 104-105 so that it is rather high. Kimura and Tsutahara simulated these phenomena by the discrete vortex method. Their simulation corresponds to very high Reynolds number flows because the diffusion of the vorticity is neglected. For a rather wide range of the Reynolds number, the initial stage of the flows about rotating circular cylinders has been studied numerically and experimentally by Badr and Dennis and Badr and Coutanceau. Who state that at a Reynolds number of 103 a periodic variation appears in the time variation of the lift for the flow at the spin parameter of unity, but no periodic variation appears for the flow at a spin parameter of 3. However, the effect of the Reynolds number on these phenomena has never been explicitly described. In this study, the effect of the rotation of the cylinder and that of the Reynolds number are investigated by experiments and numerical simulations.

Visualization of Shock Wave by Electric Discharge

Theme O PTICAL systems such as schlieren systems, MachZehnder interferometers, and shadowgraphs have been used as typical methods to observe shock waves around models. However, any shock shape cannot necessarily be observed by these optical systems. For instance, it is difficult to measure a cross-section of a shock wave around a model, especially that around a winged body as shown in Fig. 1. In this case the shock shape in the shaded region (dotted line) cannot be observed by any optical method, because a part of the optical axes is intercepted by the body. In this paper, an observing method of shock waves by using an electric discharge has been tried. The principle of the method is based on the fact that a radiation intensity of an electric discharge depends on gas densities. When an electric discharge is generated across a shock wave, the radiation intensity in the shock layer is different from that in the freestream according to the difference of each density, consequently the location of the shock wave can be easily found by taking a photograph of this discharge column. Since the location of the electrodes may be chosen arbitrarily and the discharge column can be observed from any direction, it will be expected to be able to observe cross-sectional shock shapes or the shock wave in a shaded region as stated above. W I N G E D BODY

New method for measurement of surface pressure using magnetic tape

A new method of surface pressure measurement has been developed using magnetic tape as a sensor—instead of the usual strain gage, piezogage or semiconductor —within a diaphragm-type pressure transducer. The method is based on the idea that a pressure value applied to the diaphragm is related to the deflection of the diaphragm, and the deflection can be related to the value of magnetization strength sensed in the tape. The merit of the new method is that it can be easily applied for measurement of pressure distributions on model surfaces because many pressure transducers are contained in a single sheet only about 1-mm thickness. The proposed method can be used in the high-temperature, short-duration measurement conditions, and so it is well suited to hypersonic wind-tunnel use. The sheet can be bonded onto a model surface. In this study, experiments using the new pressure sensor were performed in a hypersonic gun tunnel at a Mach number of 10 for a duration time of 10 ~2 s. Pressure distributions around two models in hypersonic flow were measured successfully.

Preliminary Study on Forward Loaded Cascades Designed With Inverse Method for Low Pressure Turbine

To reduce the number of the turbine vanes or the solidity as far as possible without increasing energy loss, the preliminary study on so called forward loaded turbine cascades had been done. These new cascades were designed for the typical velocity diagrams of the first and the second stage of a jet engine low pressure turbine. With regard to the design procedures, the improved inverse method based on the channel flow method and also boundary layer analysis technique were employed to optimize the surface velocity distributions, and then, compute the cascade geometry. These forward loaded cascades, and the stage-of-the-art aft loaded conventional ones designed for almost equivalent velocity diagrams had been tested in the High Speed Cascade Wind Tunnel of KHI’s Technical Institute. These forward loaded cascades had shown the lower kinetic energy loss coefficient characteristics and the wider useful incidence ranges over the wider region extended to the high subsonic regime comparing with the aft loaded ones, in spite of its higher loading. In addition to some main parts of the design procedures, theoretical and experimental results are discussed.Copyright

On a Pilot Pump Using the Weis-Fogh Mechanism

A pilot pump using an efficient lift-generating mechanism found in hovering flights of small insects, which is called the Weis-Fogh mechanism, was built and its characteristics were studied experimentally and it was shown that this mechanism works well for pumps. The maximum efficiency was larger than 45%. A flow visualization about the wing was performed and clusters of vortices were found to be produced periodically in the wake. Some possibilities for raising the efficiency were discussed.

Analysis of compressible flows around a uniformly expanding circular cylinder and sphere

The flows caused by a uniformly expanding circular cylinder or sphere in a perfect gas at rest at various (from small to very large) expansion velocities are analysed by a method of successive approximations in which the first approximation represents the incompressible flow. The shock waves which form around the bodies are also treated. The results for a sphere, even up to the third approximation, agree closely with Taylors (1946) calculations for all the expansion rates.

Development of a Diaphragmless shock Tunnel Using a Butterfly Valve.

A diaphragmless shock tunnel is developed using a butterfly valve, which has generally lower energy loss than that of a piston valve. The valve and its driving unit can be made from commercially available parts. Incident shock Mach numbers and stagnation pressures at the barrel end were measured and compared with those obtained when an aluminum diaphragm was used. The faster the velocity of opening of the valve (or the diaphragm), the larger the incident shock Mach number and the stagnation pressure. Moreover, uniformity of hypersonic flow in the test section was ensured by Mach number distribution based on Pitot pressure measurement. Those results show the feasibility of the valve mechanism.