Research at CeFPaC

The center has two main thrusts: (i) Aerodynamics of aerial, ground and underwater vehicles, (ii) wind energy (smart wind turbine blades, and buildings integrated wind).   

CeFPaC’s primary research areas include:

  • Flow Physics: 2-D, 3-D, and unsteady flows
  • Flow Control: Fundamental and applied experimental, numerical and theoretical investigations of flow control in macro and micro systems
  • Actuators: Design, fabrication, optimization, and modeling of actuators for flow control
  • Flow Sensing:  Flow sensors and controls to enable autonomous systems

Current Projects

sample TS cancellation

A turbulent boundary layer greatly increases the drag on a wing, and therefore aircraft fuel consumption.  By delaying the transition of organized, laminar flow into disorganized, turbulent flow, billions a year can be saved in fuel costs.  One way that this transition can be delayed is by using a vibrating surface element to suppress the Tollmien-Schlichting (TS) waves responsible.

This project focuses on the development and application of piezoelectric linear actuators in different examples of active flow control. The primary goal of this research is to build and quantify custom piezoelectric bending beam actuators; the piezoceramic used is Lead Zirconate Titanate. Different actuators with varying parameters such as piezoelectric thickness and beam length are being fabricated and tested. These devices are actuated with a periodic function, resulting in an oscillating platform on which to mount different flow control devices.

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.

Sample OFV results over a NACA0015 airfoil using static tips

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.

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.

Separation is an adverse aerodynamic effect resulting in loss of aerodynamic performance. Previous studies on separation have mainly dealt with a two-dimensional analysis due to the assumption that the third dimension was negligible or that it was too complicated to analyze, leading to an incomplete analysis on separation. However, literature has indicated that this is insufficient in understanding separation and needs to be studied as such.

Previously tested 1/19th scale vertical tail model based on Boeing 767 tail with synthetic jet actuators

The addition of active flow control devices, such as synthetic jet actuators, on three-dimensional aerodynamic surfaces (i.e. vertical tail, wings, etc.) can lead to significant flowfield modification for beneficial improvements in aerodyanmic performance.  Previous work by Dr. Nicholas Rathay and collaborators on this project focused on augmenting the side force generated by synthetic jets through separation control on scaled vertical tail models.  Since commercial airplane tails are sized based on a single engine failure situation, they are larger than necessary for normal flight.

This project is acutely focused on the fundamental fluid physics governing the unsteady loads experienced by non-streamlined objects. Bluff bodies, as they are commonly known, experience abrupt separation of the flow which subjects them to the consequences of flows which may be unsteady and in many cases, transitioning from laminar towards turbulence. Examples of bluff bodies include tall buildings, bridge decks, and slung-load containers. One archetype geometry which has proven itself to be a benchmark for other studies is the rectangular prism.

In general, the behavior in the wake of a wall-mounted circular cylinder with finite height is considerably different from that of two-dimensional bluff bodies. Unlike the flow field associated with a conventional 2D cylinder, a cantilevered finite-span cylinder is largely influenced by the presence of a spanwise (i.e., along the height of the cylinder) velocity component, most notably the downwash issued from the free end of the cylinder.

This project investigates the use of active flow control on square bluff bodies relevant to tall buildings. The research seeks to ameliorate the unsteady loading by controlling the formation and development of the von-Kármán vortex street, which is known to be the cause of undesirable building motion. More specifically, a fluidic jet is periodically excited at each of leading edges of a square prism where the shear layers separate and evolve into the large-scale vortex shedding in the wake.

Applying bio-mimicry intelligence to the aerodynamic performance of tall slender buildings has potential to lead to not only improved response to wind loading, but generate savings in material and construction costs, affect energy consumption by providing self-shading and controlling local air flow to promote local wind energy generation and ventilation strategies.

As wind turbines increase in size in order to capture more power, so do much of the adverse natural effects such as wind gusts and atmospheric turbulence. Specifically, one of the largest factors in wind turbine fatigue has been shown to be dynamic stall, a phenomena where the angle of attack seen by the turbine blade passes in and out of its stall angle, resulting in highly fluctuating blade loading. Our goal is to mitigate these loads by using active flow control to make wind turbines last longer.

Sketch of SIA concepts (a) single-disk configuration (b) dual-disk configuration

Synthetic jet actuators (SJA) are zero net mass flux (ZNMF) devices traditionally constructed by forming a cylindrical cavity with an orifice in either its side or one of its bases (See Figure 1).  Piezoelectric disks are used as either one (a) or both (b) of the bases.  The disks are then vibrated by means of AC voltages.  As the disks move inward and outward, the volume of the cavity changes and air is rapidly ingested and ejected through the orifice.