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Current Research of Dr. Robert Nelson

Dr. Nelson conducts his research at the Hessert Laboratory for Aerospace Research.

Delta Wing Aerodynamics

Delta wings are extremely efficient for supersonic and hypersonic flight. At angle of attack the flow structure on the upper side of a delta wing is dominated by the vortices created at the sharp leading edge. The structure of the leading edge vortices can undergo a substantial change called "vortex bursting" or "breakdown" as the angle of attack is increased. When leading edge vortex breakdown occurs the aerodynamic characteristics of the delta wing can change significantly. Experimental studies are being conducted to improve the basic understanding of the mechanisms causing vortex breakdown on simple and complex delta wing configurations.

Leading Edge Vortex Dynamics

The aerodynamic forces associated with maneuvering flight will not respond simultaneously with the motion of the aircraft due to the convective time lag of the adjusting flow field. The unsteady aerodynamic characteristics of slender wings are not clearly understood. For oscillatory or transient motions, the leading edge vortices exhibit hysteresis behavior in location relative to the wing and with vortex breakdown. These nonlinear aerodynamic characteristics can lead to flight instabilities such as a self-induced limit cycle roll oscillation known as "wing rock."

High Lift Flow Physics

The performance and economics of commercial transport aircraft designs is very dependent upon the high lift system design. Studies have shown that high lift technology improvements are essential for the United States to retain its leadership in the commercial transport industry.

Improved high lift system performance requires a better understanding of the flow physics associated with multi-element airfoils and wings. An experimental program to address the flow physics of high left systems is being undertaken at Notre Dame under NASA sponsorship. A research program is being conducted to investigate confluent boundary layers and relaminarization.

Flow Bifurcation and Nonlinear Flight Dynamics

The maneuvering performance of an aircraft depends on its rolling characteristics. Dynamic rolling motions such as wing rock, wing drop and heavy wing are motions that are not commanded by the pilot. These unwanted rolling motions can seriously compromise the performance and safety of the aircraft. Flow separation is believed to be the underlying cause of most flight dynamic phenomena. The goal of the research is to provide a better understanding of the flow physics that create the aerodynamic characteristics that can cause unexpected roll excursions. Nonlinear dynamical systems theory may provide a means of detecting potential flight dynamic problems early in the design phase. The relationship between critical states (flow field bifurcations) and roll instabilities will be investigated using analysis techniques developed from nonlinear dynamical systems. Of particular interest is whether identification of critical states in static aerodynamic measurements can be used to predict unwanted rolling motions.