Entrainment in the trailing edge cavity of high-lift wings

Johanna Christine Malisani, Ryerson University

Date of Award

2005

Degree Type

Thesis Project

Degree Name

Master of Engineering (MEng)

Department

Mechanical Engineering

First Advisor

Paul Walsh

Abstract

The essence of this project is a computational fluid dynamics analysis of the trailing edge cavity of high-lift wings. The objective is to investigate the effects on the resulting flow field in the trailing edge cavity as the bute's length and deflection angle are altered. Of notable interest was the effect this had on the overall performance of the wing, as indicated by the lift coefficient. Also of keen interest was the effect of flow entrainment in the trailing edge cavity on the lift coefficient. In addition to the base case, the current trailing edge device configuration, four other cases were considered for angles of attack of -5, 0, 5 and 10 degrees.

The first case analyzed was that for a bute of half-length, the second case, a bute of three-quarters length, the third case, a bute with a 25.45 degree deflection angle and the fourth case, a bute with a 45.45 degree deflection angle. All the cases were examined at a Mach number of 0.28 and compared to the base case. It was found that the 25.45 degree deflected bute case had the best lift qualities for all angles of attack. This is attributed to the fact that the high-energy flow from the bottom surface of the wing remains attached to the bute over a greater portion of it's length, thus delaying the boundary layer separation on the bute. By delaying the separation, the flow is better directed toward the slot passages of the trailing edge device, so that upper surface flow can be re-energized, stabilizing the boundary layer, and suppressing the onset of separation. It was also discovered that entrainment can be beneficial if the recirculation zones are appropriately located in the cavity, as these recirculation zones can further accelerate the high-speed flow from the bottom surface through the slot passages, to allow for greater control of the boundary layer.