Kida and Miyai's theory, which treats theoretically the problem of the minimum induced drag of nonplanar ground effect wings, is refined and extended. The gap clearance between the wing tip and the ground is assumed to be so small that the method of matched asymptotic expansions may be used. Except for this restriction, this method has a remarkable flexibility in wing front-view geometry. The theory is applied to some typical cases such as semielliptic, rectangular, and triangular ground effect wings over flat surface and a flat plate in a rectangular guide way. Special attention is concentrated on the two limiting cases with very high and low front views. Kida and Miyai's errors are corrected.

Minimum induced drag of ground effect wings

The flow field around a circular cylinder elastically suspended with a cantilever-type plate spring in the jet impingement region was visualized to investigate the mechanism of the impingement heat transfer. The impingement distance H was kept constant at 3 or 5 times as large as the jet slot width, h = 15 mm.The Reynolds number was fixed at 10,000, or 5000 in the case of flow visualization. The self-induced periodic swing motion of the cylinder across the jet axis was caused by the interaction between the jet and the elastically suspended cylinder. It was found that this swing motion has direct effects on the flow and heat transfer characteristics of the stagnation region. The ensemble-averaged values of the flow velocity and its fluctuations depended on the cylinder diameter and the impingement distance. The local Nusselt number in the case of H/h = 3 with the oscillating cylinder of the smallest diameter D = 4 mm was increased to 1.15 times as large as that without the cylinder. The interesting patterns of the intermittency function defined with a certain threshold level of turbulence intensity were obtained under the above experimental conditions. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 313–330, 2001

Flow field and heat transfer of a two‐dimensional impinging jet disturbed by an elastically suspended circular cylinder

The static instability of a slender front-free-aft-fixed elastic strip in the nuiform air stream the free end of which is the leading edge is studied analytically. The elastic strip is held vertically. The analysis is performed using the slender wing theory and beam theory and the effect of gravity force are considered that is the effect of the lateral buckling due to the gravity force. The approximate analysis is done by using energy method, and the static aeroelastic divergence speed is obtained. When the flexural rigidity approaches to the lateral buckling condition, the aeroelastic divergence speed becomes lower till zero wind speed.

Aeroelastic Divergence and Lateral Buckling of Free-Fixed Elastic Strip in Uniform Flow

The dynamic instability of an elastic supported sphere in the uniform flow is studied experimentally by using the low speed open wind tunnel. If the oscillation was made by an initial deformation due to the outer disturbance, the oscillation was damped when the wind speed was below the some critical wind speed. However, if the wind speed increased over that critical wind speed, the limitcycle oscillation appeared. This oscillation disappeared and the small amplitude randam oscillation appeared, when the wind speed increased over the another higher critical wind speed, and the oscillation of the sphere damped rapidly even if the oscillation was made by the initial deformation due to outer disturbance. In the present study, eight series of the wind tunnel tests were done i. e. the two spheres and the four pairs of the spring were used. The limitcycle dynamic instability were observed in the Reynolds number range 3×103<Re<4×104. The ratio of the limitcycle dynamic instability disappearing critical wind speed to the one appearing wind speed was between 4.8 to 2.2 in the each wind tunnel test. The maximum vibration amplitude of the sphere oscillation was about 0.5d in the each test.

Oscillation of a Spring-Supported Sphere in Uniform Flow.

The stability of a slender fixed-free elastic strip in a uniform air stream is studied analytically. The analysis is performed using slender body aerodynamic theory and beam theory. It is seen that the aerodynamic instability occurs as a result of coupling between first and second bending modes.

Yuzo Yamamoto

Papers

Oscillation of a Spring-Supported Sphere in Uniform Flow.

Flutter Analysis of Fixed-Free Slender Elastic Strip in Uniform Flow

Some Notes on the Induced Drag of Nonplanar Ground Effect Wing

Aeroelastic Divergence and Lateral Buckling of Free-Fixed Elastic Strip in Uniform Flow

Aeroelastic Divergence of Front-Free-Aft-Fixed Elastic Plate in Supersonic Flow