Center for Flow Physics and Control

Elma Center, NY, United States

Center for Flow Physics and Control

Elma Center, NY, United States
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Gildersleeve S.,Rensselaer Polytechnic Institute | Clingman D.,Rensselaer Polytechnic Institute | Clingman D.,Boeing Company | Amitay M.,Rensselaer Polytechnic Institute | Amitay M.,Center for Flow Physics and Control
AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting | Year: 2017

The implementation of an array of finite span, low aspect ratio circular pins as a flow control means to mitigate separation over a flapped airfoil was investigated experimentally in a wind tunnel. As a first step, the flowfield associated with the interaction of a single finite span, low aspect ratio static/dynamic cylindrical pin with a laminar boundary layer over a flat plate was explored. The local and global flowfields were explored for the single pin, which showed that adding a dynamic motion resulted in an increased magnitude of vortical structures associated with a low aspect ratio cylinder, increased downwash over the pin and entrainment of fluid around the cylinder sides. Additionally, the pin’s mean height is explored in a parametric study to determine the effects that the mean height of a static pin with respect to the local boundary layer imposed on the nearfield region. Results indicated that the magnitude of downwash and flow acceleration around the cylinder is directly related to its mean height and blockage effect to the free stream. The pin erected to approximately the same height as the local boundary layer appears to provide the most significant results in terms of enhanced downwash and minimal wake deficit. Lastly, the effect of an array of static cylinders, placed just upstream of a deflected control surface, on the separated flow over the control surface was explored via surface pressure and Stereo Particle Image Velocimetry measurements. The array of pins was embedded in a turbulent boundary layer, where the height of the pin was approximately ½ of the local boundary layer thickness. The static array of pins demonstrated reduction (or complete mitigation) of the separated flow over the control surface, as well as a change in the global circulation; thus, an enhancement of the lift force and reduction of drag is anticipated. Overall, the features discussed have provided strong evidence of the potential that finite span, low aspect ratio cylindrical pins provide as a new mechanism for flow control. © 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Duffin D.A.,University of Notre Dame | Duffin D.A.,Center for Flow Physics and Control | Jumper E.J.,University of Notre Dame | Jumper E.J.,Center for Flow Physics and Control
AIAA Journal | Year: 2011

A feedforward adaptive-optic correction was made on a known, repeatable aero-optical aberration caused by a two-dimensional heated jet. Since the bandwidth requirements for traditional closed-loop adaptive-optic correction are significantly higher than current technology limitations, an unconventional feedforward adaptive-optic correction scheme was experimentally tested to determine the feasibility of adaptive-optic corrections for aerooptical disturbances in general. The feedforward adaptive-optic approach was successful in correcting aero-optical disturbances at a frequency of 240 Hz, as evidenced through Shack.Hartmann wave front sensor measurements. The feedforward correction scheme exceeded simulated performance predictions when it was able to boost the timeaveraged Strehl ratio from 0.64 without correction to 0.88 with correction. © 2011 by D. Duffin and E. Jumper.

Van Buren T.,Rensselaer Polytechnic Institute | Amitay M.,Rensselaer Polytechnic Institute | Amitay M.,Center for Flow Physics and Control | Whalen E.,Boeing Company
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012

The effects of different geometries and input parameters on the flow structures of a finite span synthetic jet are explored in quiescent flow experiments using stereoscopic PIV. Common geometrical parameters, such as neck height, and orifice aspect ratio are varied along with the jet performance characteristics such as Strouhal numbers and Reynolds numbers. Orifice neck heights of 2, 4 and 6mm were tested at aspect ratios of 6, 12, and 18. Jet Strouhal numbers of 0.115 to 0.157 were tested at Reynolds numbers of 615. It is found that as the aspect ratio was increased the size of the vortical structures decreases, the vorticity dissipation rate increases, and axis switching occurred farther away from the orifice. The neck length had a large effect on the structures' size and strength, their dissipation rate, and the jet's spreading. Moreover, the driving frequency was found to affect the vortical structures spreading due to the streamwise spacing between structures, as well as drastically affecting dissipation of the structures in both planes. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

Monastero M.C.,Rensselaer Polytechnic Institute | Monastero M.C.,Center for Flow Physics and Control | Amitay M.,Rensselaer Polytechnic Institute | Amitay M.,Center for Flow Physics and Control
8th AIAA Flow Control Conference | Year: 2016

Synthetic-jet-based active flow control for separation control over a vertical tail is an ongoing area of research, the goal of which is reducing the size of the vertical tail on commercial airplanes. Before placing the actuators on an airplane, a detailed understanding of the effect different jets and test parameters have on side force enhancement must be obtained. Previous work investigated the performance enhancement of 1/19th scale and 1/9th scale vertical tail models and showed that the side force could be augmented by as much as 34%. The authors found an unexpected relationship between jet spacing (and number of jets) and side force enhancement that did not agree between the two models, where, under specific conditions, increasing the spacing between actuators increased the side force on the larger 1/9th scale model while decreasing it on the smaller 1/19th scale model. To further understand the interactions among jets as spacing varied, a new model was designed and tested in the Rensselaer Polytechnic Institute (RPI) Subsonic Wind Tunnel. The model was designed such that it is capable of varying sweep angle, rudder characteristics (chord length and deflection), and various actuator parameters. The experiments discussed in this paper focus on the unswept case with the rudder at a moderate deflection angle of 20o and the sensitivity of the side force produced by the unswept model to different parameters. The flow field around the new model was first characterized using particle image velocimetry and pressure measurements. The effect of synthetic jet flow control was found to significantly modify the pressure distribution globally around the model, which resulted in up to 17% improvement in the side force. The effect of sideslip angle and jet spacing were also studied and found to agree with the trends observed in previous work. The work discussed here is the foundation for continuing tests on a swept configuration of the model. These future tests will study how the addition of spanwise flow and variations in separation severity affect the performance trends as spacing is varied. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

Vasile J.D.,Rensselaer Polytechnic Institute | Amitay M.,Rensselaer Polytechnic Institute | Amitay M.,Center for Flow Physics and Control
52nd Aerospace Sciences Meeting | Year: 2014

An experimental investigation was performed to study the three-dimensional flow interaction of a finite-span synthetic jet located near the tip of a sweptback wing (crosssectional profile of the NACA 4421, AR = 4, sweep angle of 30°), at a Reynolds number of 105 and at three angles of attack of 0°, 9° and 15.5° (covering the range of attached to separated flow in the vicinity of the jet). Three blowing ratios were considered, 0.8, 1.2 and 2. Stereoscopic Particle Image Velocimetry (SPIV) data were collected at multiple 2-D planes in the vicinity of the jet’s orifice, which were then used to reconstruct the flow volume. The effect of the jet’s blowing ratio was analyzed using time-averaged and phase-averaged statistics. The study showed that the flow field in the vicinity of the synthetic-jet orifice becomes highly three-dimensional and is governed by the streamwise structures that are associated with the finite span of the orifice (edge vortices). The presence of a wing tip vortex results in the development of a non-uniform (in the spanwise direction) spanwise boundary layer that becomes more pronounced with increasing angle of attack. Consequently, the development of the jet and the associated flow structures are altered. © 2014, American Institute of Aeronautics and Astronautics Inc. All rights reserved.

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