Ilan Fono

Suction and Oscillatory Blowing Actuator Modeling and Validation

Enhancing the ability to control flows in different configurations and flow conditions can lead to improved flow-related, energy-efficient systems. Certain active flow control actuators are effective at low Mach numbers, but the momentum and vorticity they provide limits their utilization to low speeds. At higher Mach numbers, robust, unsteady, effective, and practical fluidic actuators are a critical, enabling technology in any flow control system, though they are largely missing. A new actuator concept, based on the combination of steady suction and oscillatory blowing, is presented. The actuator achieves near-sonic speeds at a frequency range from 10 Hz to at least 1 kHz. It has no moving parts and therefore is expected to have superior effectiveness and reliability. The operating principles of the new actuator are presented along with two computational models and their experimental validation.

Large trucks drag reduction using active flow control

Aerodynamic drag is the cause for more than two-thirds of the fuel consumption of large trucks at highway speeds. Due to functionality considerations, the aerodynamic efficiency of the aft-regions of large trucks was traditionally sacrificed. This leads to massively separated flow at the lee-side of truck-trailers, with an associated drag penalty of at least a third of the total aerodynamic drag. Active Flow Control (AFC), the capability to alter the flow behavior using unsteady, localized energy injection, can very effectively delay boundary layer separation. By attaching a compact and relatively inexpensive “add-on” AFC device to the back side of truck-trailers (or by modifying it when possible) the flow separating from it could be redirected to turn into the lee-side of the truck, increasing the back pressure, thus significantly reducing drag. A comprehensive and aggressive research plan that combines actuator development, computational fluid dynamics and bench-top as well as wind tunnel experiments was performed. The research uses an array of 15 newly developed Suction and Oscillatory Blowing actuators housed inside a circular cylinder attached to the aft edges of a generic 2D truck model. Preliminary results indicate a net drag reduction of 10% or more.

Closed-Loop Vectoring Control of a Turbulent Jet Using Periodic Excitation

Closed-loop control strategies were studied experimentally at low Reynolds and incompressible Mach numbers using periodic excitation to vector a turbulent jet. Vectoring was achieved by attaching a short, wide-angle diffuser at the jet exit and introducing periodic excitation from a slot covering one quadrant of the circumference of the round turbulent jet. Closed-loop control methods were applied to transition quickly and smoothly between different jet deflection angles. The frequency response of the zero-mass-flux piezoelectric actuator was flat to about 0.5 kHz, but the jet responds up to 30-50 Hz only. This is still an order of magnitude faster than conventional thrust vectoring mechanism. System identification procedures were applied to approximate the systems transfer function. A linear controller was designed that enabled fast and smooth transitions between stationary deflection angles and maintained desired jet vectoring angles under varying system conditions. The linear controller was tested over the entire range of available deflection angles, and its performance is evaluated and discussed.

Roll control via active flow control: from concept to flight

This paper describes a series of experiments that enabled a flight demonstration of roll control without moving control surfaces. That goal was achieved using a wing with a partial span Glauert-type airfoil, characterized by an upper-surface boundary-layer separation from the two-thirds chord location at all incidence angles. The flow over that region was proportionally controlled using zero-mass-flux unsteady excitation emanating from piezofluidic actuators. The control was applied to one wing at a time, resulting in gradual suppression of the boundary-layer separation, increased lift, and reduced drag, leading to a coordinated turning motion of the small electric drone. The extensive multidisciplinary study (starting from the actuator adaptation, the airfoil integration, and the two dimensional wind-tunnel tests) led to the selection of a configuration for the flight demonstrator. Further development of a lightweight wing and piezofluidic actuators, along with a compact, lightweight, energy-efficient electronic drive system, was followed by full-scale wind-tunnel tests and three successful flight tests. It was flight demonstrated that active flow control can induce roll moments that are sufficient to control the vehicle flight path during cruise, as well as during landing. A linear model was used to predict the roll motion of the active-flow controlled drone, with reasonable agreement to the flight-test data. The current study resulted in several pioneering (to the best of our knowledge)achievements that should pave the way to further integration of active-flow-control methods in flight vehicles for hingeless flight attitude and flight-path control, as well as improved performance and increased reliability with lower observability.

Suction and Oscillatory Blowing Actuator

Enhancing the ability to control flows in different configurations and flow conditions can lead to improved systems. Certain active flow control (AFC) actuators are efficient at low Mach numbers but the momentum and vorticity they provide limits the utilization to low speeds. At higher Mach numbers, robust, unsteady, efficient and practical fluidic actuators are a critical, largely missing, enabling technology in any AFC system. A new actuator concept, based on the combination of steady suction and oscillatory-blowing (SaOB) is presented. The actuator can achieve near-sonic speeds at about 1 kHz. It has no moving parts and therefore is expected to have superior efficiency and reliability. The operation principle of the SaOB actuator is presented along with two predictive computational models and their experimental validation.

Experimental Validation of Sensor Placement for Control of a D-Shaped Cylinder Wake

The effectiveness of a sensor configuration, based on body mounted sensors, for feedback flow control of a D-shaped cylinder wake is investigated experimentally. The research is aimed at suppressing unsteady loads resulting from the von Karman vortex shedding in the wake of bluff bodies at a Reynolds number range of 100-1000. A low-dimensional Proper Orthogonal Decomposition (POD) procedure was applied to the stream-wise and cross-stream velocities in the near wake field obtained using Particle Image Velocimetry (PIV) with steady state vortex shedding. The data was collected from the unforced condition, which served as a baseline, as well as during influence of forcing but within the “lock-in” region. The design of sensor number and placement was based on data from a laminar direct numerical simulation of the Navier Stokes equations. A Linear Stochastic Estimator (LSE) was employed to map the surface mounted sensor signals to the temporal coefficients of the reduced order model of the wake flow field in order to provide accurate yet compact estimates of the low-dimensional states. For a three sensor configuration, results show that the root mean square estimation error of the first two cross-stream modes is within 20 – 40% of the PIV generated POD time coefficients. This level of error is acceptable for a moderately robust controller required to close the loop, based on previous investigation.