Acoustics Shock Vibration Signal Processing September 2011 Newsletter Wake Turbulence by Tom Irvine Figure 1. Wingtip Vortices Introduction Meanwhile air curls up over the wing tips and then Airflow over an aircraft’s wings generates of pair of flows from the top of the wing downward, creating counter-rotating vortices, as shown in Figure 1. down wash, as shown in Figure 2. The two flow The vortices are hazards to other aircraft following effects combine at the wingtip and create a fast behind in the wake, or crossing through the wake. spinning vortex similar to horizontal tornadoes, A particular concern is that the trailing aircraft may trailing the aircraft. experience severe displacement and acceleration, Characteristics causing loss of control, structural damage, or even The main characteristics of aircraft wake vortices a fatal crash. are: Sink rate: 300 to 500 feet/minute Flow Mechanism Stabilization at 500 to 900 feet under the aircraft at The air pressure above the wing is less than the air the origin of the vortices pressure below the wing during flight. This is Lateral movement at 5 knots when reaching the necessary for lift. The high-pressure air below the ground wing flows upward to the low pressure region. Life span: 30 seconds to a few minutes The fuselage blocks this flow, so the path of least depending on the aircraft’s size, weight, speed resistance is toward the wingtips. and wing shape, as well as the wind conditions
Acoustics Shock Vibration Signal Processing September 2011 Newsletter Wake Turbulence by Tom Irvine Figure 1. Wingtip Vortices Introduction Airflow over an aircraft’s wings generates of pair of counter-rotating vortices, as shown in Figure 1. The vortices are hazards to other aircraft following behind in the wake, or crossing through the wake. A particular concern is that the trailing aircraft may experience severe displacement and acceleration, causing loss of control, structural damage, or even a fatal crash. Flow Mechanism The air pressure above the wing is less than the air pressure below the wing during flight. This is necessary for lift. The high-pressure air below the wing flows upward to the low pressure region. The fuselage blocks this flow, so the path of least resistance is toward the wingtips. Meanwhile air curls up over the wing tips and then flows from the top of the wing downward, creating down wash, as shown in Figure 2. The two flow effects combine at the wingtip and create a fast spinning vortex similar to horizontal tornadoes, trailing the aircraft. Characteristics The main characteristics of aircraft wake vortices are: Sink rate: 300 to 500 feet/minute Stabilization at 500 to 900 feet under the aircraft at the origin of the vortices Lateral movement at 5 knots when reaching the ground Life span: 30 seconds to a few minutes depending on the aircraft’s size, weight, speed and wing shape, as well as the wind conditions
September2011_NL.docx