Two-dimensional Laser Doppler Velocimeter Research Articles

Turbulence Characteristics of Supersonic Turbulent Boundary Layer Reattaching downstream of Backward-Facing Step.

The aim of this paper is to clarify the turbulence characteristics of the supersonic boundary layer which is reattaching downstream of a backward-facing step. The boundary layer flow was analyzed by a two-dimensional laser Doppler velocimeter and flow visualizations. The results showed that there was a higher level of momentum exchange between the reattaching boundary layer flow and the main supersonic stream than that of over a flat plate case. Numerical simulation was conducted in this flow field, and the results were compared with the experimental ones. It was clarified that the present CFD code exhibits good performance of simulation for the mean characteristics of flow field, and it was suggested that the improvement of the compressible turbulence model was needed.

Fluid Flow Phenomena in a Cylindrical Bath Agitated by Top Lance Gas Injection.

Fluid flow phenomena in a cylindrical bath agitated by gas injection from a submerged top lance were investigated on the basis of cold model experiments. A swirl motion of liquid, which was sumilar to the rotary sloshing, was observed under a certain blowing condition. The critical condition for the cessation of the swirl motion was first experimentally clarified and subsequently the following experiments were made in the absence of the swirl motion. The vertical migration distance of bubbles from the lance exit was measured using an electro-resistivity probe, and an empirical correlation for it was proposed as a function of the modified Froude number. The axial and radial velocity components of liquid were measured for a water-air system using a two-dimensional laser Doppler velocimeter. Applicability of previous emperical correlations of the axial mean velocity proposed for the gas injection through a centric bottom bozzle to the present case was examined. An electro-chemical method was used to measure the mass transfer coefficient between a platinum flat plate and aqueous FeSO4 solution. In the region below the bubble plume, the so-called dead water region was observed.

上吹き浸漬ランスからのガス吹込みを伴う円筒浴内の流動現象

Fluid flow phenomena in a cylindrical bath agitated by gas injection from a submerged top lance were investigated on the basis of cold model experiments. A swirl motion of liquid, which was similar to rotary sloshing, was observed under a certain blowing condition. The condition was experimentally clarified and subsequently the following experiments were made for cases without swirl motion. The vertical migration distance of gas from the lance exit was measured using an electro-resistivity probe and an empirical correlation of the migration distance was proposed as a function of the modified Froude number. The axial and radial velocity components of liquid phase were measured for a water-air system using a two-dimensional Laser Doppler Velocimeter. Applicability of the previous correlations of axial mean velocity proposed for gas injection through a centric bottom nozzle to the present case was examined. An electrochemical method was used to measure the mass transfer coefficient between a platinum flat plate and aqueous FeSO4 solution. In the axial region below the bubble plume, the so-called dead water region was observed.

Turbulent separated reattached flow in a two-dimensional curved-wall diffuser

A turbulent separation-reattachment flow in a two-dimensional asymmetrical curved-wall diffuser is studied by a two-dimensional laser doppler velocimeter. The turbulent boundary layer separates on the lower curved wall under strong pressure gradient and then reattaches on a parallel channel. At the inlet of the diffuser, Reynolds number based on the diffuser height is 1.2×105 and the velocity is 25.2m/s. The results of experiments are presented and analyzed in new defined streamline-aligned coordinates. The experiment shows that after Transitory Detachment Reynolds shear stress is negative in the near-wall backflow region. Their characteristics are approximately the same as in simple turbulent shear layers near the maximum Reynolds shear stress. A scale is formed using the maximum Reynolds shear stresses. It is found that a Reynolds shear stress similarity exists from separation to reattachment and the Schofield-Perry velocity law exists in the forward shear flow. Both profiles are used in the experimental work that leads to the design of a new eddy-viscosity model. The length scale is taken from that developed by Schofield and Perry. The composite velocity scale is formed by the maximum Reynolds shear stress and the Schofield-Perry velocity scale as well as the edge velocity of the boundary layer. The results of these experiments are presented in this paper.

Experimental measurements of the flow in a scramjet inlet at Mach 4

Wind-tunnel measurements have been carried out in a scramjet inlet model at a freestream Mach number of 4.00. Measurements included velocity profiles using a two-dimensional laser Doppler velocimeter (LDV), Mach number surveys, skin friction measurements with Preston probes, wall static pressure distributions, density profiles with a laser holographic interferometer, and qualitative shadowgraph photography. The effect of boundary-layer bleed on the viscous flow entering the inlet was also investigated. It was determined that bleeding off the boundary layer increased the inlet efficiency substantially.

Measurement of Velocities in Solitary Waves

The water surface profiles and corresponding water particle velocities of several solitary waves have been obtained. The measurements of the horizontal and vertical velocity components are conducted using a two-dimensional laser-Doppler velocimeter (LDV). Results are presented for three different wave height-to-depth ratios: ϵ = 0.11, 0.19 and 0.29. The experimental results are compared with existing theories which follow different orders of approximation, and the theories are found to agree well with the experiments. It has been convincingly demonstrated that the LDV measurement technique offers an unmatched advantage to determine the water particle velocities under water waves, especially in the region above the still water level.