Flows through the passage between two parallel discs from inner to outer radii accompanying strong circumferential swirl have been investigated in view of flow stability in vaneless diffuser of centrifugal pumps and compressors. Particular concern is on the phenomenon of rotating stall which is observed as the flow rate is reduced to a critical value. Experiments have been carried out and the results have been put in order, showing (i) diffuser characteristics, (ii) streamline and vorticity distributions, (iii) loss coefficients, (iv) stall cell propagation speed and fluctuation amplitude, (v) rotating pressure patterns, wherefrom a proposition has been made for explaining the mechanism of stall cell propagation.
In order to examine the supersonic mixing process in a high enthalpy supersonic flow, the shock tunnel using the quick-action valves has been developed and confirmed their operation. The present shock tunnel enables to make a high enthalpy flow without contamination in high reproducibility by easy operation. The nozzle is designed to make parallel supersonic flows which are comprised of high-enthalpy air stream and helium stream. Mach number of air and helium flow are 3.4 and 4.2, respectively. The structure of mixing region of parallel supersonic flows thus obtained was examined by means of the mass-sampling probe which enables one to examine directly the concentration ration of the mixture gases. The measurement shows that the mixing region almost agrees with the region observed by Schlieren photograph.
Damage and residual strength of [0°/90°/45°/-45°]s graphite/epoxy composite laminated plates subjected to normal impacts were investigated experimentally. A steel ball of 10mm or 12mm in diameter was collided with the composite plate with an air gun in the velocity range of 5m/s-40m/s. Delaminations were evaluated by two methods. One was a destructive inspection using fluorescent penetrant: the impacted plate was cut off, and placed in fluorescent liquid for one night. It was then dried and peeled off lamina by lamina and ultra violet rays were projected on it. The other method was SAM (Scanning Acoustic Microscopy) which made it possible to distinguish delamination portions on different interfaces non-destructively by adjusting the focus of the acoustic lens and the gate timing for the reflected wave history. The following results were obtained: delaminations were generated only on interfaces where neighboring fiber directions are orthogonal i. e. on 1/2, 3/4, 5/6, 7/8 interfaces, where the first lamina was the impact side and the 8th lamina was the back side. The delamination areas of the interfaces which were further from the impact side were larger, i. e. 1/2<3/4<5/6<7/8. However, a damaged area distinguished on the outer surface of the 8th lamina was smaller than the delamination area on the 7/8 interface, therefore it is possible that some extent of delamination exists on the inner interface even though no damage can be recognized visually. The residual strength of impacted composite plates was evaluated by a four-point bending test. Bending strength seemed to begin to decrease at the same time that the delamination started to be generated.
Methods for calculating induced drag are divided into two main categories, “Near Field Method (NFM)” and “Far Field Method (FFM).” “Conventional Vortex Lattice Method (VLM)” gives not-so-good results when NFM is used, because of its poor prediction of leading-edge suction forces. Some patch-works for it have been published, all of those results however are more or less unsatisfactory; only method holding consistency and rationality may be the Quasi-VLM by C. E. Lan. This paper reports the results of the induced drag calculated by BIS (Box-In-Strip), a new numerical lifting surface method developed by the present authors. Both leading-edge suction forces in NFM and Manglertype singular integral in FFM are evaluated satisfactorily. Analytical evaluation of the induced drag for elliptical wings, in steady incompressible flow, is devised referring to the Kida's theory. BIS yields excellent correlation with analytical solutions for both of NFM and FFM on elliptic planform wings. Besides BIS gives closer agreement between the calculated results by NFM and FFM than Quasi-VLM for the general wing planforms.