Etsuo Morishita

Effects of an air stream on turbulent diffusion of a helium jet from a small nozzle

In a round helium jet with a small nozzle, and a Reynolds number of 2.95 × 103, with and without an air stream, mean profiles, instantaneous fluctuations, and correlations of velocity and matter are investigated using the hot‐wire technique. The characteristic difference in the behavior of the jet due to the presence of an air stream is extensively studied and summarized as follows: (1) Similarity in mean profiles is not reached at least in terms of r/z and the spreading and decay of the jet follow some slower laws, and (2) lateral turbulent diffusion is reduced while active axial turbulent diffusion is induced in the middle of the distribution of the jet. The correlations between fluctuations are established as a whole, but those between concentration and velocity fluctuations are reduced in the lateral direction. It seems that the turbulent motion of large eddies plays an important role in the transport mechanism of the flow field.

Spreadsheet Fluid Dynamics for Aeronautical Course Problems

Computational Fluid Dynamics is now used daily in scientific and engineering practices. Thecomputations themselves are now based on commercially available software. Personal computersare widely utilized elsewhere these days and many people are using spreadsheets as well as wordprocessors. It is now well known to the scientific and engineering communities that spreadsheets canbe used, not only for statistics and data processing calculations, but also for matrix inverse,iteration in a finite difference equation, and for special functions of mathematics. This situationallows us to realize SFD, i.e., Spreadsheet Fluid Dynamics. The authors have demonstrated thatthe fluid dynamics equations could be solved efficiently by using a spreadsheet. The cells in thespreadsheet are viewed as either natural grids in CFD or elements of a matrix. The computationaldomain corresponds to the real physical shape and/or the computational space by grid generation.The result can be visualized on the same spreadsheet with inherent graphics. The pre- and post-processors are all in one in SFD.

Biplane Aerodynamics Revisited

Biplane is a classical aerodynamic problem. In this paper, we first introduce a well-known simple analytical method based on a pair of vortices on each airfoil. This method give a pretty accurate result in spite of its simplicity. We then revisit Moriya’s conformal mapping approach which is an exact analytical solution. This method is an old one with some mathematical beauty and the present author think that it is worthwhile to repeat it here, because it was written in his native language and possibly not known to the rest of the world. We finally use the modern discrete vortex method for comparison. The lift ratio, a biplane to two isolated airfoils, is obtained as a function of pitch and stagger.

Schwartz-Christoffel Panel Method Improvements and Applications

Schwartz-Christoffel panel method is improved and applied to general and unique airfoils. A potential flow around a two-dimensional circular cylinder can be transformed to that of a two-dimensional airfoil by the Schwartz-Christoffel conformal mapping. Multiple straight panels approximate a two-dimensional airfoil. This method is particularly effective for very thin airfoils. The conventional panel method would suffer for these extremely thin airfoil problems. First, the method is improved and tested against a circular cylinder and the analytical Joukowski airfoil. Several real airfoils are studied together with the unique polygonal airfoil sections for the propeller of Mars exploration and the dragonfly airfoil. It is shown that the method gives satisfactory results for all cases.

Unsteady Aerodynamic Characteristics of Deformable Airfoil

The transient aerodynamic characteristics of a deformable two-dimensional airfoil during a stepwise incidence variation were studied experimentally. The instantaneous aerodynamic forces of the deformable airfoil were higher than those of the non-deformable one primarily due to the unsteady deflection of the deform-able airfoil. The pressure distributions on the airfoil surface were obtained. The flow around the deformable airfoil was also visualized with a high speed camera.

Some design problems of scroll compressor.

The design problems of scroll compressors are discussed in this paper. The critical machine element of scroll compressors is the thrust bearing when the compressors are employed for air conditioning and refrigeration, viz, very long time operation. Not only the thrust but also the moment act on the thrust bearing. The theory of Rumbarger is applied to describe the load condition of the thrust bearing. How to optimize the geometric shape of the spiral elements is also the prime interest of the designers. It is explained in this paper that the spiral geometry is able to be optimized when the stability condition, weight, thrust and outer diameter of the orbiting scroll are taken into account. The optimum design would minimize the overturning moment of the orbiting scroll when the outer diameter of the thrust bearing is predetermined.