A study of an unsteady characteristic of a supersonic jet flow issuing from annular nozzle was performed by an experiment and numerical analysis. The influence that the nozzle shape of the center part of the annular nozzle exerted on the flow and the pressure vibration was clarified by the experiment. Furthermore, the vortex formed in low-pressure region of the flow of the nozzle exit was clarified by the numerical analysis. Especially, it was clarified that the nozzle shape influenced the vortex and pressure vibration.

View full abstract

This report has aimed to control the boundary layer of the flow. Especially, the research on the control of the separation point of the jet flow was done about the jet flow issued from the divergent nozzle in the region from the subsonic jet flow to the supersonic jet flow. The boundary layer of the jet flow was controlled by the control flow and the position of the separation point was controlled by this method. Moreover, the frequency analysis of total pressures was done by the experiment.
Furthermore, to examine the separation point of the flow issued from the divergent nozzle, the numerical analysis was done. Consequently, an unsteady characteristic of the flow was clarified. And, it was clarified that the boundary layer control influenced the total pressure. As a result of the numerical analysis, it was found that the control flow influenced the separation of the flow and the position of the separation point was different according to the stagnation pressure.

View full abstract

The aim of the present paper is to clarify the flow structure in a coaxial jet with axisymmetric and helical instabilities for low Reynolds number. The flow visualization and the measurements of mean and fluctuating velocities by the particle image velocimetry (PIV) technique were carried out in an open water tank. The Reynolds number based on the outer diameter and the mean velocity of the annular jet was 3000. The mean velocity ratio was 0.65. For the coaxial jet with helical instability, it was found that the streamwise velocity along the centerline of the jet decreased more than that of the coaxial jet with axisymmetric instability, and the amplitude of the velocity fluctuation was small near the nozzle exit. This shows that the increase of the velocity fluctuation in the outer mixing region is associated with the arrangement of the vortexstreet in the shear layer.

View full abstract

An annular impinging jet was used to enable uniform cooling over a wide area of a flat wall. The ratio of an inner diameter to an outer one of a coaxial pipe was fixed at 0.64. The ratios of the inner pipe gas flow to the outer one, velocity ratio, were varied from 0 to 1.0 for the fixed outer pipe gas flow at 20m/s. The heat transfer characteristics on the impinging wall were examined. For the purpose of uniform cooling, the optimum velocity ratio was found to be approximately 0.1. The influence of the velocity ratio on the flow structure was clarified by the flow visualization.

View full abstract

This study is to clarify the flow structure of a three-dimensional wall jet discharged tangentially on a flat surface from a circular nozzle. Instantaneous pattern of the secondary flow was visualized by tuft-grid methods, and the feature of the large-scale structures existed in the present wall jet was examined. It was revealed from cross-section views that the streamwise vortices with the scale as large as that of the jet height were dominant structures, and that these vortices were moving quasi-periodically toward the outside. And also, a surface flow was visualized with the depth-tuft grid. A dynamic behavior of the streamwise vortices was excellently shown in terms with the tuft image reconstructed at x/d ?? 40 and its two-dimensional spectrum.

View full abstract

In this paper, a window-deformation PIV was proposed in order to measure high shear-rate flows. For proper deformation, an appropriate velocity gradient tensor must be obtained. In the present approach, a method to extrapolate the velocity gradient from the region with higher reliability velocity was proposed. As a result of evaluation by using artificial images, it was found that the proposed method can be measure high-shear rate flows with little outliers.

View full abstract

A cellular neural network (CNN) algorithm is introduced in the particle pairing process of the 3-D particle tracking velocimetry. Unlike the Hopfield neural network, each neuron is connected only to its neighbors and thereby the time required for learning is drastically reduced with respect to its counterpart. In order to establish a single step profile of 3-D velocity, this neural network is used three times: two time of stereoscopic particle pairing and one more time of time-differential particle pairing. In the stereoscopic particle pairing, the network uses object functions aiming at minimization of the sum of the epipolar-line normal distances. In contrast, the time-differential particle pairing uses more abject functions, indicating minimization of the sum of the Euclid distances between the particles as well as smoothness of the velocity variance over the measurement field and rigidity of particle distribution patterns,

View full abstract