Evolution of vortical structures behind an inclined flat plate

2D3C TR-PIV technique was utilized to investigate streamwise-oriented vortical structures behind an inclined flat plate. The angle of attack was set to 7 deg, several fields of view in the wake were investigated. The instantaneous velocity vector fields were captured, dynamics of the flow was studied using POD method. The streamwise structures are determined by vorticity and low- and high-velocity streaks are defined. The acquired results are in a good agreement with the new hypothesis of a principle of flight.

Echo-PIV Measurement Around the Pump System in the Nuclear Reactor

Echo-PIV system was applied to measure the velocity fields of a pump system inside the nuclear reactor model. The scale-downed model of pump system driven by a motor was built for this study. 2D instantaneous velocity vector fields of the downstream region of impeller were obtained. The flow rate was calculated and compared with the result from the flow meter. From this study, the feasibility of echo-PIV for studying the opaque flow in the fluid machinery was shown.

Analysis of Instantaneous Turbulent Velocity Vector and Temperature Profiles in Transitional Rough Channel Flow

The instantaneous velocity vector and instantaneous temperature in a turbulent flow in a transitionally rough channel have been analyzed from unsteady Navier–Stokes equations and unsteady thermal energy equation for large Reynolds numbers. The inner and outer layers asymptotic expansions for the instantaneous velocity vector and instantaneous temperature have been matched in the overlap region by the Izakson–Millikan–Kolmogorov hypothesis. The higher order effects and implications of the intermediate (or meso) layer are analyzed for the instantaneous velocity vector and instantaneous temperature. Uniformly valid solutions for instantaneous velocity vector have been decomposed into the mean velocity vector, and fluctuations in velocity vector, as well as the instantaneous temperature, have been decomposed into mean temperature and fluctuations in temperature. It is shown in the present work that if the mean velocity vector in the work of Afzal (1976, “Millikan Argument at Moderately Large Reynolds Numbers,” Phys. Fluids, 16, pp. 600–602) is replaced by instantaneous velocity vector, we get the results of Lundgren (2007, “Asymptotic Analysis of the Constant Pressure Turbulent Boundary Layer,” Phys. Fluids, 19, pp. 055105) for instantaneous velocity vector. The comparison of the predictions for momentum and thermal mesolayers is supported by direct numerical simulation (DNS) and experimental data.

Ultrasonic Measurement of Instantaneous Velocity Vector Profile

This paper proposes a new technique that enables the measurement of an instantaneous velocity vector profile in multi-dimensions on a line of the flow field. A system to achieve this goal was developed based on ultrasonic velocity profiling (UVP) by using multiple transducers. A focusing transducer, which reduces the effective diameter of ultrasonic beams around the focal point, was used to minimize the spatial uncertainty in the measurement. A two-dimensional system was constructed by using a normal transducer as a receiver and a focusing transducer as both an emitter and a receiver, and successfully applied to an actual flow field, rigid body motion of fluid in a rotating cylinder, for two-dimensional velocity vector measurements. To estimate the influence of existence of an intermediate wall, acoustic field under the developed system was computed by solving two-dimensional wave equation and then the focal point of an ultrasonic beam was determined to optimize the system. The system was applied to measure two dimensional velocity components of a periodic velocity fluctuation in a wake of a cylinder in a shallow channel as an example of unsteady flow. Obtained temporal variation of velocity vector profile confirmed an applicability of the developed system to unsteady flow. The vortex shedding in the wake was well reproduced as in the vorticity distribution, which was computed from the temporal variation of the vector field using Taylor frozen hypothesis. Although a temporal resolution is still not high, we conclude that applicability of the measurement system has been confirmed.

Interpreting Orthogonal Triple-Wire Data From Very High Turbulence Flows

For turbulence intensities of up to 30 percent, an orthogonal triple-wire probe can be used to make accurate measurements of the instantaneous velocity vector. Above this limit difficulties arise in the interpretation of the data due to the problem described as rectification. This paper presents a means by which data from an orthogonal triple-wire probe may be interpreted for single point measurements in Gaussian turbulence with intensity up to 50 percent resulting in unbiased estimates of the velocity mean vector, Reynolds stress tensor, and time correlation coefficients.