Aerodynamics

Enhanced aerodynamic performance that avoids flow separation on wing surfaces has been traditionally achieved by appropriate aerodynamic design of airfoil sections.  However, when the wing design is driven by non-aerodynamic constraints (stealth, payload, etc.) the forces and moments of the resulting unconventional airfoil shape may be much smaller than on a conventional airfoil.  Therefore, either active or passive flow control techniques can be used to enhance aerodynamic performance throughout the flight envelop.

Although passive control devices, such as vortex generators, have proven, under some conditions, to be quite effective in delaying flow separation, they offer no proportional control and introduce a drag penalty when the flow does not separate (or when they are not needed).

In contrast, active flow control enables coupling of the control input to flow instabilities that are associated with flow separation and thus may enable substanial control authority at low actuation levels.  Furthermore, active actuation is largely innocuous except when activated and has the potential for delivering variable power.  In previous studies, active control efforts have employed a variety of techniques including external and internal acoustic excitation, vibrating ribbons or flaps, and steady or unsteady blowing.

Over the past couple of decades, the synthetic jet actuator has emerged as a versatile actuator for active flow control.  The formation and evoluation of synthetic jets are described in detail in the work of Smith & Glezer (1998), Glezer & Amitay (2002), Amitay and Cannelle (2006), Van Buren et al. (2014).  The effectiveness of fluidic actuators based on synthetic jets is derived from the interaction of these jets with the flow near the flow boundary that can lead to the formation of a quasi-closed recirculating flow region, resulting in a virtual modification of the shape of the surface.

The aerodynamic research at CeFPaC has several objectives:  (1) understand the flow physics of the flow field of the system in question, (2) understand the flow mechanisms associated with the interaction between the flow and the actuators, (3) explore, experimentally and numerically, the feasibility of using active flow control for flight control, (4) develop low order models of the flow, and (5) develop a closed-loop control schemes.

dynamic vortex generators
Dynamic Vortex Generators
Currently many vertical tails on commercial aircraft are oversized in order to compensate for an extremely rare and specific emergency scenario: A single engine out in high crosswind during takeoff and landing. Our goal is to improve the performance of a smaller vertical tail, which would allow for higher deflection angles, and therefore higher sideforce, in order to compensate for the high yaw produced during these emergency scenarios. This would allow for a significant decrease in weight and drag, since the majority of an airplanes flight time is spent at cruise conditions.
Representation of EAPs on a Micro Air Vehicle
Electroactive-Polymer-Based Flow Control at Low Reynolds Numbers
Micro air vehicles (MAV) are a major focus of aerodynamics today with many military as well as civilian applications. MAV flight is dominated by the unsteady characteristics of low Reynolds number flows. In this work an Electro-Active Polymer (EAP) actuator was examined as a feasible flow control actuator with application to low Reynolds number flows. The actuation of the EAP was found to be very effective in altering the boundary layer as well as mitigating laminar separation bubbles.
Experimental Investigation and Characterization of Stall Cell Formation
Experimental Investigation and Characterization of Stall Cell Formation
Drones and High Altitude Long Endurance vehicles typically operate at moderate to high Reynolds numbers based on airfoil chord length, i.e., Rec ≈ 105 to 106. These vehicles are becoming increasingly important to applications like national security-related surveillance, search and rescue in dangerous terrain, scientific research, and animal conservation, among others. As such, the understanding flow conditions in such a way to ensure the safety of these aircraft is of paramount importance.
Fail-Safe actuator
Fail-Safe Actuator
Passive (vortex generator) and active (a pair of synthetic jets) devices have been used in unison to create a Hybrid “fail-safe” device, which proved to be more effective than either device on its own and is the focus of this study.
Finite Span Cylinder
Finite Span Cylinder
The effectiveness of a finite span synthetic jet oriented parallel to the freestream direction, actuated on a finite span cylinder of low aspect ration and issuing normal to the cylinder surface was investigated experimentally using stereoscopic particle image velocimetry (SPIV), surface pressure measurements, and hotwire anemometry.
Schlieren Experiments
Flow Control in a Transonic Diffuser through Mass and Vorticity Injection to Mitigate Massive Separation
Compact inlets with an S-shape have become widely used in aircrafts due to the numerous advantages compared to conventional ducts. However, due to their low length to diameter ration and low aspect ration, there are some flow phenomena, which are undesirable such as massive separation leading to losses in total pressure and secondary flow structures causing distortion at the Aerodynamic Interface Plane (AIP). These drawbacks need yet to be overcome in order to apply these ducts on a wider range of vehicles.

Center for Flow Physics and Control
Mechanical, Aerospace & Nuclear Engineering
School of Engineering, Rensselaer Polytechnic Institute
Watervliet Facility, 805 25th Street, Watervliet, NY USA 12189
Phone: (518) 276-2481 Fax: (518) 276-2728

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