Editor-in-Chief: Dr. Surya Raghu
published quarterly ISSN 1756-8250 2012 journal prices/format options
2012 is volume 4
The ability to control and manipulate fluid flows to reap technological benefits has a wide range of applications in both man-made and natural systems that have fluid flow in or around them. In recent years, flow control has become a highly multi-disciplinary research activity encompassing theoretical, computational and experimental fluid dynamics, acoustics, control theory, physics, chemistry, biology and mathematics.
In the field of aerospace engineering, the aerodynamic design of future civilian and military aerospace vehicles will be greatly influenced by flow control technologies available for jet engine inlet and exhaust systems, thrust vectoring, weapons-bay cavity flow/acoustics, impingement jet noise reduction, and propulsion devices such as jet engines and rockets. These flow control systems will be used in a variety of flow situations to modify the shear layers and control mixing, energize the boundary layers to control flow separation, produce jet deflections, and to control resonant cavity oscillations. Control of boundary layer transition in both low speed and high speed ablating and non-ablating conditions is also an important area of flow control. Associated with high-speed flows is also the control of aero-optics effects. Flow control in turbomachinery is needed to increase efficiency of thrust and power generation while reducing environmental footprints. Efficient combustor designs and stable compressor flows using flow control are needed for such purposes. The turbomachinery noise can be reduced by controlling the wake-rotor-stator interactions. In the area of alternative energy technologies, flow control over the wind turbine blades will lead to higher efficiencies of such systems. Progress in biomimetic flight systems could be based on new ideas for flow control in unsteady situations.
Drag reduction in trucks and passenger vehicles could decrease fuel consumption, there by reducing their pollution footprints into the environment.
In the field of biomedical engineering, modification of the flow properties of the blood for drag reduction in the arteries by addition of polymers/chemistry control in the blood could reduce the number of heart attacks or strokes due to clotting. Advanced drug delivery systems could be designed on the basis of our ability to control certain fluid properties and trajectories by direct physical manipulation or remote control of either the delivery systems or the fluids of interest.
In the field of chemical engineering, flow control could mean control of mixing to obtain highly efficient and controlled chemical reactions and development of chemical reactors based on new mixing control technologies.
Currently, the literature on flow control is spread over several journals - AIAA Journal, Journal of Aircraft, ASME/JSME Journal of Fluids Engineering, Physics of Fluids, Experiments in Fluids, Int. J. of Heat and Fluid Flow Gas Turbine Engineering, Journal of Fluid Mechanics, Combustion Science and Technology, SAE, etc. It is the objective of this International Journal of Flow Control to provide a forum for publication of articles covering all of the above areas in one place and is hoped that this will increase the cross-pollination of ideas on flow control into the various sub-disciplines. This will also reduce the time spent on searching for flow control articles in the all the journals.
Active Yaw Control of a Ducted Fan-Based MAV
Kiyoshi Otani1, William Gressick2, and Michael Amitay3
1National Defense Academy, School of Systems Engineering, Department of Aerospace Engineering, Hashirimizu 1-10-20, Yokosuka-shi, Kanagawa-Pref, Japan 239-8686
2Center for Automation Technologies and Systems, Rensselaer Polytechnic Institute, Troy, NY
3Mechanical, Aerospace and Nuclear engineering, Rensselaer Polytechnic Institute, Troy, NY. Corresponding Author; E-mail: email@example.com
The feasibility of using active flow control to stabilize a micro ducted fan unmanned aerial vehicle in a yaw motion was investigated experimentally. Flow control was implemented using synthetic jet actuators to manipulate the flow around the vehicles stator vanes. As a result, this mechanically simplified control approach can be used to yaw the vehicle instead of moving control surfaces and articulated rotor blades. The rotational control of the MAV (165.5mm in diameter and 177.8mm in height) was obtained activating surface-mounted synthetic jets that were flush mounted on a set of four fixed stators downstream of the duct. The synthetic jets were located downstream of a deliberately formed local separation to enable controlled flow reattachment. The flow field around the stators and in the wake was studied using particle image velocimetry (PIV) where the geometrical angle of attack of the stators is either 0o or 6o and the propeller rotational speed is either 4,200RPM or 9,000RPM (generating 2.2N or 8.8N, respectively). The torque generated by the propeller and the counter-torque induced by the combined stators-synthetic jets were measured using a load cell. Activation of the synthetic jets resulted in a partial or a full flow reattachment and thus a controlled increase and decrease of the lift and drag forces, respectively, induced on the stators. The modification of the aerodynamic forces yielded a rotational torque that counteracted the torque generated by the propeller. A closed-loop controller with gyroscopic feedback was implemented to regulate the yaw rate to zero and reject disturbances caused by changes in propeller speed.
Flow Control Using Synthetic Jet and Plasma Actuators on a Rotorcraft
Tail Boom Model
Sarah J. Haack
Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
Alison B. Flatauy
University of Maryland, College Park, MD, 20742, USA
This paper shows the time-averaged effect of synthetic jet and plasma actuators
over a representative two-dimensional rotorcraft tail boom for delaying flow separation
and, therefore, reducing pressure drag, whereas previous studies have evaluated these flow
control devices on a circular cylinder. The percentage of pressure drag reduction is used to
evaluate the effectiveness of these two unique actuators for varied applied voltage, actuator
position and flow velocity. Two non-dimensional parameters were used to evaluate the
e®ect of the actuators: coefficient of momentum (Cµ) and non-dimensional surface distance
between the location of the actuator and the flow separation point (SDC). Both actuation
techniques beneficially a®ect the pressure distribution by decreasing the pressure near the
location of the actuators and increasing the pressure in the separated flow region. Contour
plots displaying the variation of the percentage of pressure drag reduction as Cµ and SDC
vary illustrate optimal operating conditions based on these parameters.
Successes and Challenges for Flow Control Simulations
Christopher L. Rumsey
NASA Langley Research Center, Hampton, VA 23681-2199, USA
A survey is made of recent computations published for synthetic jet flow
from a CFD workshop held in 2004. The three workshop cases were originally cho-sen
to represent different aspects of flow control physics: nominally 2-D synthetic jet
into quiescent air, 3-D circular synthetic jet into turbulent boundary-layer crossflow, and
nominally 2-D flow-control (both steady suction and oscillatory zero-net-mass-flow) for
separation control on a simple wall-mounted aerodynamic hump shape. The purpose of
this survey is to summarize the progress as related to these workshop cases, particularly
noting successes and remaining challenges for computational methods. It is hoped that
this summary will also by extension serve as an overview of the state-of-the-art of CFD
for these types of flow-controlled flow fields in general.
Experimental and Numerical Investigation of Active Control of Inlet Ducts
John Vaccaro, Onkar Sahni, Joseph Olles, Kenneth Jansen, and Michael Amitay
Mechanical, Aerospace and Nuclear Engineering Department,
Rensselaer Polytechnic Institute, Troy, NY 12180, USA
Active flow control, via steady control jets, was implemented to improve the performance of a very aggressive (length to exit diameter ratio, L/D, of 1.5) inlet duct. Experiments were performed for a range of inlet Mach number from 0.2 to 0.45, with the latter simulated with computation. A brand new facility was designed and built to enable various actuation methodologies as well as multiple measurement techniques. In the present work, a pair of steady control jets was placed in streamwise locations where flow was expected to separate. Static pressure measurements, along the upper and lower walls of the duct, were performed for various combinations of actuation. The forcing level of the control jets as well as combinations of jets, were tested. In addition, total pressure measurements were conducted at the Aerodynamic Interface Plane (AIP) to obtain the distribution of the pressure recovery and compared to the results from the computation. The computational domain includes the full 3D geometry to precisely match to the experimental facility. Flow control was shown to have a substantial effect, mainly on the lower wall. It was found to be more effective at the lower Mach number where the blowing ratio was higher (for the same mass flux ratio). The data suggest that using 2-D flow control to affect a flow field that is highly three-dimensional is not optimal, and as such a spanwise varying actuation should be implemented.
Helmholtz Powered Resonance Tube Actuator
Authors: Ganesh Raman, Alan Cain and Edward Kerschen
A powered resonance tube actuator consists of a jet aimed at the open end of a tube that is closed at the other end. Large self-sustained oscillations can be produced without any moving parts and the frequency can be varied by changing the depth of the tube. In some applications that require relatively low actuator frequencies, geometrical constraints may be incompatible with the use of a quarter-wavelength resonance tube. Note that the resonance tube length is inversely proportional to the resonant frequency, and is therefore quite long for the case of low resonant frequencies. A Helmholtz resonator can achieve low frequencies without such large linear dimensions, by combining a narrow neck with a backing cavity of much larger cross section. For the Helmholtz resonator, the fluid in the narrow neck provides the mass, while the compressibility of the fluid in the backing cavity provides the spring constant. The frequency can be lowered by increasing the mass in the neck, or by increasing the capacitance of the backing cavity. Two theories for Helmholtz resonator behavior have been developed (Kerschen et al), the axial-wave theory and the low-frequency theory. In both theories, the cross-sectional dimensions of the resonator neck and cavity are assumed small compared to the acoustic wavelength. This allows transverse wave motion to be ignored in the analysis, leading to significant simplifications. Our work experimentally demonstrates the working of a Helmholtz powered resonance tube actuator and shows that numerical simulations, theory and experiment are in good agreement. Quantitatively, however, the simulations are predicting an slightly lower than the theoretical values for all but one of the cases simulated here. It is not yet clear why this is the case. It is possible that the limitations of the axi-symmetric and laminar assumptions are hampering the simulations. Alternatively, it may be that neglecting the mean flow in the theory is causing some error. Also, the end corrections for the neck are based on semi-infinite range for the flared neck. Since the flare only extends a short distance, this assumption might need to be modified.
Flow Measurement and Control of Orifice Free Jet (Effect of Nozzle Contraction)
Shakouchi, T., Kito, M., Sakamoto, T., Tsujimoto, K. and Ando, T.
Graduate School of Engineering, Mie University, Kurimamachiya-cho 1577, Tsu-shi, Mie 514-8507, Japan
Abstract. Nozzle configuration may offer the possibility of a passive control technique to provide high mixing and heat transfer rates. Thus, numbers of investigations have been carried out to reveal the influence of nozzle configuration on the flow characteristics. However, there are only several researches regarding orifice jets can be found. Despite the evidence indicating that orifice jets improve the mixing and heat transfer characteristics, we were unable to find a systematic study of them that focused on the contraction area ratio. The effects of varying the contraction area ratio CR from 1.00 to 0.11 on the flow characteristics of a free jet issuing from an orifice nozzle were examined. The large vortex structure of a submerged orifice water jet was visualized by the tracer method, which indicated the coherent vortex structure was highly affected by the CR value. The mean and fluctuating velocities of the orifice air jet were also measured using a single hot-wire and the effects of CR on them were demonstrated. It is found that the normalized centerline maximum velocity could be expressed by uc/um= 1.9 CR3 3.55 CR2 + 1.38CR + 1.53, showing a maximum value of 1.7 at CR=0.27. In addition, the high spreading and entrainment rates were obtained for smaller value of CR indicating that the potential of an effective passive control technique.
Dr. Surya Raghu,
Advanced Fluidics LLC, 8860 Columbia 100 Parkway, Suite 204,
Columbia, MD 21045
Prof. Thomas C. Corke, University of Notre Dame, Notre Dame, IN 46556, USA
Prof. Mohamed Gad-el-Hak, Virginia Commonwealth University, USA
Professor Ann R. Karagozian, UCLA, Los Angeles, CA 90095-1597, USA
Prof. Dr.-Ing. Rudibert King, Technische Universität Berlin, 10623 Berlin, Germany
Prof. Mohammad Samimy, The Ohio State University, USA
Prof. Anuradha Annaswamy, Massachusetts Institute of Technology, USA
Prof. Jean-Paul Bonnet, Université de Poitiers, France
Prof. Louis N. Cattafesta, University of Florida, USA
Dr. Tom Crittenden, Georgia Tech/VAST, USA
Prof. David Greenblatt, Technion, Israel Institute of Technology, Israel
Prof. James W. Gregory, Ohio State University, USA
Dr. John C. Lin, NASA Langley Research Center, USA
Prof. Graham 'Gus' Nathan, The University of Adelaide, Australia
Prof. Ganesh Raman, Illinois Institute of Technology, USA
Prof. Toshihiko Shakouchi, Mie University, Japan
Dr. Michael J. Stanek, Air Force Research Laboratory, USA
Mr. Xunnian Wang, China Aerodynamics Research and Development Center, P.R.China
Prof. Hong Yan, Northwestern Polytechnical University, P.R.China
Prof. Xin Zhang, University of Southampton, UK
Manuscripts should be sent to the editor: flowcontroljournal@ gmail.com