Experimental and numerical study of an airfoil in combination with a cross flow fan

Abstract

In this article, the airfoil comprising a cross flow fan has been studied at various boundary conditions by experiment and numerical solution. The airfoil generates high lift at low forward speeds and shows excellent potential for short take off and landing and vertical take off and landing. According to the experiments, lift and pitching moment coefficients of the airfoil increase and its drag coefficient reduces with the fan rotational velocity. The pitching moment coefficient enhancement demonstrates that the aircraft is more stable at higher rotational speeds. Experiments showed that the aerodynamic coefficients decrease with the free stream Reynolds number. Flow field over the airfoil has been studied by the computational fluid dynamics technique and compared with the experimental data. Numerical solution was in good agreement with the experiments. Solution showed that skin friction coefficient on the airfoil bottom wall is not sensitive to the rotational velocity, but on the upper surface, especially inside the casing, it is deeply influenced by the fan speed, while it increases with the Reynolds number on the both surfaces. According to the numerical solution, the static pressure difference between the airfoil surfaces increases with rotational velocity demonstrating higher lift coefficients at higher fan speeds, and also increases with the Reynolds number that is equivalent to the enhancement of the aerodynamic forces as shown by the experiments. Because of a sharp edge a sudden jump was observed in the pressure distribution on the airfoil upper wall. By replacing this sharp edge with a smooth and round one this pressure jump reduced significantly and pressure distribution on the modified surface became smoother and its extremal value diminished considerably. The streamlines on the upper surface were closer than those on the bottom surface indicating higher pressure on the airfoil bottom wall. They became closer on the airfoil upper surface when fan speed increased. In addition, velocity gradient on the airfoil surfaces increased with the Reynolds number that is tantamount to a higher skin friction coefficient. Discrepancies between numerical and experimental data can be attributed to measurement uncertainty in the experiments and convergence precision in the numerical solution, two-dimensional solution in the computational fluid dynamics and three dimensionality of the flow at the wing tips in reality.