Yoshihiro Matsuoka

Behavior of a Confined Plane Jet in a Rectangular Channel at Low Reynolds Number I. General Flow Characteristics

The detailed characteristics of confined symmetric, asymmetric and wall jets at low Reynolds numbers were studied using the visualization technique and laser Doppler velocimetry. The behavior of these three different types of jet was found to be characterized by the aspect ratio of the rectangular channel used. Thus, no differences among the jets were found regarding the separation, the reattachment length and the conditions of instability of the jet flows. Furthermore, the three-dimensional effect of the flow was examined in detail by visualizing the secondary flow. The velocity distributions across the channel were measured by laser Doppler velocimetry and compared with those obtained by numerical analysis.

Behavior of a Plane Jet at Low Reynolds Number Confined in a Rectangular Channel II. Two Solutions by Numerical Analysis

Streamlines of confined symmetric and asymmetric channels at low Reynolds numbers were numerically analyzed by means of successive over-relaxation upwind schemes. Two different flow patterns were obtained for the same Reynolds number. These results gave examples in cases where the solution of the Navier-Stokes equation is not unique for the same Reynolds number. However, for a symmetric channel, one of these flow patterns with symmetry is unstable and makes a transition to the other asymmetric pattern.

Numerical Analysis of Open-Channel Flows

Turbulent flow characteristics of open channel flows over a weir were analyzed by the volume of fluid(VOF) and the, κ-e turbulent model. The VOF method was employed in order to represent the free surface by Eularian mesh. The effects of the weir shape and the Reynolds number were discussed in detail. It was found that the shape of free surface at the downstream of weir was affected by the height and crest width of weir. The height of free surface were greatly affected by the selection of the void fraction on numerical analysis.

Flow Visualization and Numerical Calculation in a Curved Diffuser. Effects of Existence of a Guide Vane.

In our previous experiments using a wind tunnnel, the flow in a two-dimensional curved diffuser with logarithmic spiral angle was clarified quantitatively about the variation of spiral angle and the existence of a guide vane. The wind tunnel method however requires much time for preparation of the experimental system and for the main experimental procedure.We have recently devised a new experimental method for identifying optimum diffuser forms in less time than that required by the conventional technique. This new method involves visualization of flow (using dye streaks and condensed milk) and numerical calculation using the finite element method. The results obtained with this new method were compared with those obtained with the wind tunnel method to assess its usefulness.The results of numerical calculation approximately agreed with the findings from flow visualization. The analysis using this method showed that the flow in the diffuser was improved by the existence of a guide vane, although some differences were observed depending on the magnitude of the logarithmic spiral angle. These findings are consistent with those obtained in our previous wind tunnel experiments. This method involving flow visualization and calculation is therefore expected to provide a simple and useful means of determining ideal forms of curved diffusers.

Study on Control of Jet Attachment

A numerical study is performed on control of jet attachment by parallel controlling jet. The analysis of this study was carried out for the several combination models in the width of controlling jet nozzle over a wide range of the flow rate ratio between main jet and controlling jet. The k-e turbulence model was chosen to calculate the velocity. The results obtained were as follows; the attachment distance of jet was increase with increasing flow ratio and flow direction changed discontinuously, and attachment distance decreased in high flow rate ratio region with increasing flow ratio. These numerical results gave fairly good agreement with the experimental results.

Effect of Fin Arrangement on Flow in Pipe

In this paper, the numerical analysis of the flow with heat transfer in two-dimensional pipe attached fins was studied. The analysis was carried out for the several of combination models in the length and the number of fin over a wide range of Reynolds number. The k-e turbulence model was chosen to calculate the velocity and temperature. The results obtained were as follows; the temperature differences between the inlet and outlet decreased and presented distinction each other with increasing Reynolds number, the pressure drag coefficient was constant approximately in each pipe, and temperature difference and pressure drag coefficients were especially influenced by long fin.

Interference Characteristics of Two Parallel Supersonic Jets Issuing from Pipes with Different Diameters.

In this work, the interference characteristics of two parallel underexpanded jets issuing from straight circular pipes with different diameters were studied. Further, the influence of the distance between the central axes of the two pipes on the interference of jets was investigated. The inner diameters of the pipes used were 4.1 and 6.1 mm, and 6.1 and 9.1 mm, respectively. Flow visualization and measurement of velocity distributions were conducted ; thus, the mechanism of pseudo-shock waves and equivelocity diagrams within a vertical section to the jets axes were clarified. As a result, it was found that the longitudinal vibration of flow was controlled by the difference between the cell lengths of the two jets. Thus, the supersonic flow was present in a considerably farther downstream range than the case with two parallel jets with equivalent inner diameter.

Numerical Analysis of Flow with Heat Transfer in Pipe

In this paper, the numerical analyses of the flow with heat transfer flow in pipe having fins were studied. The analyses were carried out for the several of combination models in the length and interval of fin over a wide range of Reynolds number. The k-e turbulence model was chosen to calculate the velocity and temperature. The results obtainded were as follows ; (a) the temperature differences between the inlet and outlet decreased and presented distinction each other with increasing Reynolds number, (b) the pressure drag coefficient was constant approximately in each pipe, and differ greatly from each other.

An Experimental Investigation of the Flow in a Curved Diffuser. Effects of the Position of the Leading Edge of a Guide Vane Interposed in a Diffuser with Uniform Inlet Velocity Distribution.

This paper deals with an experimental study of the flow in a logarithmic spiral curved diffuser with uniform inlet velocity distribution. In this study, the effects of the variation in the interposed position of the guide vane in a diffuser and the position of its leading edge on the pressure distributions along both diffuser walls, velocity and vector distributions, and the diffuser efficiency are clarified. The results obtained from this study are summarized as follows : In the case where the ratio, bn/B1, of the distance bn between the convex wall and the interposed position of the guide vane at the diffuser inlet to the diffuser inlet breadth B1 is in the region of about 0.25∼0.375, the diffuser efficiency indicates the most desirable value. When the leading edge of the guide vane is placed upstream, superior diffuser efficiency can be obtained, in every interposed position of a guide vane.

FLOW VISUALIZATION USING DYE-STREAK METHOD AND NUMERICAL CALCULATION IN THE CURVED DIFFUSER

The purpose of this study is to clarify the flow pattern in the curved diffuser and to improve its performance using dye-streak method.In this study, when the diffuser inlet velocity profile is increased towards the diffuser convex wall, the effects of the interposed position and position of leading edge of a guide vane on the flow patterns in a logarithmic spiral curved diffuser are clarified by. the flow visualization using dye-streak method, and streak lines obtained are compared with the numerical solutions obtained by the finite element method.As the results, it was found that the flow patterns obtained by the flow visualization agreed comparatively with numerical results, in case a guide vane was interposed and the performance of the curved diffuser was affected considerably by the position of leading edge.of a guide vane.