Increase In Lift Coefficient Research Articles

Numerical study of a linear shear flow past a rotating cylinder

Abstract The effects of shear rate on flow past a rotating circular cylinder in a linear shear flow have been investigated by using a hybrid vortex method at a Reynolds number of 1000. The velocity gradient of the shear flow K ranges from −0.3 to 0.3 and the rotational to translational speed ratio α is 0.5. The results show that the form of vortex shedding is controlled by the shear parameter K . The drag coefficient decreases with increasing | K |. On the other hand, the lift coefficient and Strouhal number increase as K increases. As K increases, the separation positions shift downstream, the wake becomes narrower and the amplitude of fluctuation of the instantaneous lift and drag coefficients decreases.

Discrete vortex method analysis of the wall effect on a separated flow past an elliptic cylinder.

The wall effects on a separated flow past an elliptic cylinder are numerically investigated by a method combining the discrete vortex method with the image one. Present results for the mean drag and lift coefficients and the pressure distribution are in fairly good agreement with previous experimental data. The mean drag and lift coefficients and the fluctuating lift coefficient increase with the increase of blockage ratio, but their increasing rates depend on the axis ratio of the elliptic cylinder and its angle of attack. The Strouhal number increases slightly with the blockage ratio, but its increasing rate is small compared to that of the rectangular cylinder.

The effect of trailing edge extensions on the performance of the Göttingen 797 and the Wortmann FX 63-137 aerofoil sections at Reynolds numbers between 3 x 105 and 1 x 106

SummaryThe effect of trailing edge extensions was tested for the twodimensional Göttingen 797 and Wortmann FX 63-137 aerofoil sections with smooth surfaces at chord Reynolds numbers from 3 x 105 to 1 x 106 in the 8ft x 6ft low speed wind-tunnel at the Cranfield Institute of Technology. Force measurements were made on the basic aerofoil sections and with extension plates of 10% and 20% chord set tangential to the upper surface at the trailing edge. It was verified that the addition of an extension plate effectively brings about an increase of maximum lift coefficient and an improved lift-to-drag ratio for the Göttingen aerofoil section. However, the effect of the extension plate was small on the Wortmann aerofoil section.

Fluid dynamics of airfoils with moving surface boundary-layer control

Effectiveness of the moving surface boundary-layer control is assessed with reference to a symmetrical Joukowsky airfoil modified with a leading-edge rotating cylinder. Results of the test program and the numerical models suggest the following: 1) The surface singularity method is essential in modeling the complicated flow. With the inclusion of the boundary-layer correction scheme, it becomes an effective tool for obtaining useful information concerning moving surface boundary-layer control. The predicted pressure distributions are in good agreement with experiment almost up to the point of complete separation from the airfoil surface, except in the separation region, where the prediction of separated boundary layers with flow reversal would require the solution of the full Navier-Stokes equations. 2) The concept of moving surface boundary-layer control appears quite promising. The tests showed a significant improvement in maximum lift and stall characteristics. With cylinder rotation, the flow never separated completely from the upper surface for angles of attack as high as 48 deg. The higher rates of rotation (UC/U>1, Uc = cylinder surface velocity, U = freestream velocity) promoted reattachment of the partially separated flow, giving an increase in lift coefficient by as much as 150% for Ue/U = 4.

Flow around a pair of circular cylinders arranged side by side at high Reynolds numbers.

Flow and aerodynamic characteristics of a pair of circular cylinders arranged side by side in a uniform flow were experimentally studied at high Reynolds numbers near and over the critical one. Pressure distributions, lift and drag coefficients and Strouhal numbers were measured at different spacings in a wind tunnel. There are good agreements between the present results and others at subcritical Reynolds numbers. At high Reynolds numbers over critical one, we examined the relationships among the formation of separation bubbles, the aspect of wakes, and the lift and drag coefficients. Separation bubbles are formed only on the outward sides of two cylinders at small spacings and this leads to a positive and significant increase in lift coefficient, and biased flow with a high Strouhal number like at subcritical Reynolds numbers cannot be observed to appear.