Kazuo Matsuuchi

Unsteady flow field around a human hand and propulsive force in swimming

Much effort has been undertaken for the estimation of propulsive force of swimmers in the front crawl. Estimation is typically based on steady flow theory: the so-called quasi-steady analysis. Flow fields around a swimmer, however, are extremely unsteady because the change direction of hand produces unsteady vortex motions. To evaluate the force correctly, it is necessary to know the unsteady properties determined from the vortex dynamics because that unsteadiness is known to make the force greater. Unsteady flow measurements were made for this study using a sophisticated technique called particle image velocimetry (PIV) in several horizontal planes for subjects swimming in a flume. Using that method, a 100 time-sequential flow fields are obtainable simultaneously. Each flow field was calculated from two particle images using the cross-correlation method. The intensity of vortices and their locations were identified. A strong vortex was generated near the hand and then shed by directional change of the hand in the transition phase from in-sweep to out-sweep. When the vortex was shed, a new vortex rotating in the opposite direction around the hand was created. The pair of vortices induced the velocity component in the direction opposite to the swimming. Results of this study show that the momentum change attributable to the increase in this velocity component is the origin of thrust force by the hand.

Unsteady hydrodynamic forces acting on a robotic arm and its flow field: Application to the crawl stroke

This study aims to clarify the mechanisms by which unsteady hydrodynamic forces act on the hand of a swimmer during a crawl stroke. Measurements were performed for a hand attached to a robotic arm with five degrees of freedom independently controlled by a computer. The computer was programmed so the hand and arm mimicked a human performing the stroke. We directly measured forces on the hand and pressure distributions around it at 200 Hz; flow fields underwater near the hand were obtained via 2D particle image velocimetry (PIV). The data revealed two mechanisms that generate unsteady forces during a crawl stroke. One is the unsteady lift force generated when hand movement changes direction during the stroke, leading to vortex shedding and bound vortex created around it. This bound vortex circulation results in a lift that contributes to the thrust. The other occurs when the hand moves linearly with a large angle of attack, creating a Kármán vortex street. This street alternatively sheds clockwise and counterclockwise vortices, resulting in a quasi-steady drag contributing to the thrust. We presume that professional swimmers benefit from both mechanisms. Further studies are necessary in which 3D flow fields are measured using a 3D PIV system and a human swimmer.

Unsteady hydrodynamic forces acting on a robotic hand and its flow field.

This study aims to clarify the mechanism of generating unsteady hydrodynamic forces acting on a hand during swimming in order to directly measure the forces, pressure distribution, and flow field around the hand by using a robotic arm and particle image velocimetry (PIV). The robotic arm consisted of the trunk, shoulder, upper arm, forearm, and hand, and it was independently computer controllable in five degrees of freedom. The elbow-joint angle of the robotic arm was fixed at 90°, and the arm was moved in semicircles around the shoulder joint in a plane perpendicular to the water surface. Two-component PIV was used for flow visualization around the hand. The data of the forces and pressure acting on the hand were sampled at 200Hz and stored on a PC. When the maximum resultant force acting on the hand was observed, a pair of counter-rotating vortices appeared on the dorsal surface of the hand. A vortex attached to the hand increased the flow velocity, which led to decreased surface pressure, increasing the hydrodynamic forces. This phenomenon is known as the unsteady mechanism of force generation. We found that the drag force was 72% greater and the lift force was 4.8 times greater than the values estimated under steady flow conditions. Therefore, it is presumable that swimmers receive the benefits of this unsteady hydrodynamic force.

Unsteady hydrodynamic forces acting on a hand and its flow field during sculling motion

The goal of this research is to clarify the mechanism by which unsteady forces are generated during sculling by a skilled swimmer and thereby to contribute to improving propulsive techniques. We used particle image velocimetry (PIV) to acquire data on the kinematics of the hand during sculling, such as fluid forces and flow field. By investigating the correlations between these data, we expected to find a new propulsion mechanism. The experiment was performed in a flow-controlled water channel. The participant executed sculling motions to remain at a fixed position despite constant water flow. PIV was used to visualize the flow-field cross-section in the plane of hand motion. Moreover, the fluid forces acting on the hand were estimated from pressure distribution measurements performed on the hand and simultaneous three-dimensional motion analysis. By executing the sculling motion, a skilled swimmer produces large unsteady fluid forces when the leading-edge vortex occurs on the dorsal side of the hand and wake capture occurs on the palm side. By using a new approach, we observed interesting unsteady fluid phenomena similar to those of flying insects. The study indicates that it is essential for swimmers to fully exploit vortices. A better understanding of these phenomena might lead to an improvement in sculling techniques.

Numerical and experimental investigations of human swimming motions

ABSTRACT This paper reviews unsteady flow conditions in human swimming and identifies the limitations and future potential of the current methods of analysing unsteady flow. The capability of computational fluid dynamics (CFD) has been extended from approaches assuming steady-state conditions to consideration of unsteady/transient conditions associated with the body motion of a swimmer. However, to predict hydrodynamic forces and the swimmer’s potential speeds accurately, more robust and efficient numerical methods are necessary, coupled with validation procedures, requiring detailed experimental data reflecting local flow. Experimental data obtained by particle image velocimetry (PIV) in this area are limited, because at present observations are restricted to a two-dimensional 1.0 m2 area, though this could be improved if the output range of the associated laser sheet increased. Simulations of human swimming are expected to improve competitive swimming, and our review has identified two important advances relating to understanding the flow conditions affecting performance in front crawl swimming: one is a mechanism for generating unsteady fluid forces, and the other is a theory relating to increased speed and efficiency.

Research and Development on Cycloidal Propellers for Airships

Cycloidal propellers are known to be high thrust propulsors. They generate thrusts by controlling cyclically attack angles of rotating blades. In addition, they have characteristics of omni-directional and instantaneous control capabilities to yield high thrusts from small input power. We have been working to analyze their performances for several years. Experimental tests on thrust and power consumption measurements were performed with a three bladed propulsor, and indoor flight tests were carried out on an airship of 20 meters in length with a pair of these thrusters, and its flight performances were evaluated.

Investigation of the Unsteady Mechanism in the Generation of Propulsive Force While Swimming Using a Synchronized Flow Visualization and Motion Analysis System

The highly efficient locomotion of birds, insects and fish is based on unsteady dynamics. The central mechanism in their locomotion is related to the unsteady behaviour of vortices such as the formation and shedding of boundary layers developed on their bodies. The relation between an object and vortex movement was first noticed in the field of aeronautics. The problem of a thin aerofoil performing small lateral oscillations in a uniform stream of an incompressible fluid, which is at the heart of all flutter prediction, has received interest for many years. A great deal of research within the scope of the linear perturbation theory has been published in past times. Well-documented summaries can be seen in Bisplinghoff et al. (1955). Recently, significant attention has been given to the lift-sustaining flight of insects and birds despite their weight, and many fruitful discoveries have been made. Flow unsteadiness was found to play an important role in the flights. However, the unsteady mechanism in swimming propulsion has received relatively little interest. The first important contribution related to the mechanism of propulsion in a swimming stroke was made by Counsilman (1971), who divided the force of a swimming stroke into two components: a lift component normal to the hand motion and a drag component parallel to it. He pointed out the greater importance of lift force rather than drag force. The next critical contribution was made by Schleihauf (1979), who measured the lift and drag forces on hand models for various geometrical configurations of flow. Berger et al. (1995) carried out similar measurements using hand and arm models in fixed geometrical configurations within a flow and obtained the results consistent with those of Schleihauf. Subsequently, Bixler and Riewald (2002) used a numerical approach under a scenario similar to the experiments described above. Each of the approaches mentioned above can be termed a quasi-steady analysis, which depends on the assumption that the flow at each instance is nearly steady. Studies using flow visualisation have revealed the importance of a rotating water mass (Ungerechts (1981)), which focused attention on the contribution of vortices in propulsion.

On the force and vortex shedding on a circular cylinder from subcritical up to transcritical Reynolds numbers.

Pressure distribution and vortex shedding were measured in a cryogenic wind tunnel from subcritical up to transcritical Reynolds numbers(105 ≤ Re ≤ 107 ) and Mach numbers up to 0.3 without changing experimental arrangement. Drag coefficients were calculated using pressure distributions. Pressure distributions and drag coefficients show characteristic changes for subcritical, lower transition, critical, under transition and transcritical Reynolds number ranges respectively. Strouhal number takes constant value with an increase in Reynolds number for 105 ≤ Re < 3.2 × 105. Narrowband vortex shedding could not be measured in the critical Reynolds number range ( 3.2 × 105 ≤ Re ≤ 6.9 × 105). It was also measured again in the upper transition and transcritical Reynolds number ranges. Spectra of the pressure distributions and velocity fluctuations measured are presented for several characteristic values of Reynolds numbers. Results are also compared with those of the other authors.

Suppression Effect of Vortex Generator Jets With Non-Circular Orifices on Separating Flow

Jets issuing through small holes in a wall into a freestream have proven effective in the control of boundary layer separation. Longitudinal (streamwise) vortices are produced by the interaction between the jets and the freestream. This technique is known as the vortex generator jet method of separation or stall control because it controls separation in the same general way as the well-known method using solid vortex generators. The vortex generator jet method is active control of flow separation that has the ability to provide a time-varying control action to optimize performance under wide range of flow conditions. In this study, the suppression effect of the jet orifice shape of vortex generator jets on flow separation in the diffuser is investigated for three types of jet orifice (circular, triangle and square orifices). The triangle orifice makes strong the vorticity of longitudinal vortices and effective the pressure recovery in the diffuser in comparison with the other orifice shapes. Furthermore, it is found that the orifice shape of vortex generator jets causes the different tendency of the pressure recovery in the downstream direction.Copyright

Competition between dispersion and nonlinearity in deep water waves

A simple wave system consisting of a fundamental wave and its second harmonic has been studied for infinitely deep water waves. Two competing effects of the waves, nonlinearity and dispersion, were investigated. These two effects make up the behavior of the second harmonic complex. From a stability consideration in phase space it was clarified that trajectories displaced with a small amount deviate from the original ones. The asymptotic aspect of the Stokes wavetrain, which is the steady wave solution, was also discussed.