WorldCat Identities


Works: 17 works in 20 publications in 1 language and 20 library holdings
Publication Timeline
Management and Control of Unsteady and Turbulent Flows( Book )

2 editions published between 1988 and 1991 in English and held by 1 WorldCat member library worldwide

Progress in four areas of research has been achieved during the first year. I. Controlled Transitioning Boundary Layers: phase coupled plane TS waves and oblique waves are used to study various types of transition including detuned modes. II. Turbulent Boundary Layer Structure and Control: the structures responsible for the turbulence production in high Reynolds number boundary layers have been documented and manipulated. III. Management of Unsteady and Three-dimensional Flows: flows over airfoils, axisymmetric forebodies, vortex-wing interactions, and wing-body junctions, are examined with and without passive and active flow manipulators including zero-mass base bleed. IV. Scanning Laser Anemometry: a technique capable of mapping the flowfield in a plane has been developed. Keywords: Unsteady flow, Separated flow, Flow control, Instrumentation. (aw)
Coupled Experimental and Theoretical Investigations of Instability, Chaos and Turbulence in an Axisymmetric Jet Flow( Book )

1 edition published in 1990 in English and held by 1 WorldCat member library worldwide

This work focused on instability, routes to chaos, and transition to turbulence in an axisymmetric jet. The research focused on three basic tasks. The first involved the search for evidence of low dimensional strange attractors in a naturally excited condition. The theoretical analog was the construction of low-dimensional model equations for this flow. The second involved 3-D (non-axisymmetric) periodic forcing of the jet to lead to the enhanced growth of 3-D modes. This was to focus on natural resonant mechanisms involving natural instability modes of the shear layer and jet core. The theoretical analysis for this part was to predict the conditions for the most resonant interactions, which would maximize our ability to control the jet outcome. The third task was to integrate the previous tasks to exploit important mode interactions which lead to strong nonlinear regimes and or random or chaotic states. In this phase, we accomplished this through intrinsic forcing of the jet by 'enhanced feedback'. The results of the work have covered all these tasks, and yielded many new fundamental results basic to dynamical systems with feedback
Equipment to Upgrade the Facilities of the IIT (Illinois Institute of Technology) Fluid Dynamics Research Center( Book )

1 edition published in 1988 in English and held by 1 WorldCat member library worldwide

We are currently approaching the completion of the National Diagnostic Facility at IIT. The facility is based on a computer-controlled wind tunnel with a test section 4 ft. high, 5 ft. wide and 36 ft. long exhibiting very high quality flow conditions under both constant and oscillating free-stream velocity conditions. The funding of this facility was initiated under a 1983 DOD University Research Instrumentation Program (AFOSR-Grant-83-0339). A key aspect of the wind tunnel design is the manner in which heat energy produced by fan inefficiencies, is removed from the recirculating tunnel air. This involves the first use of turning vanes which also act as heat transfer elements. The system is sized to allow continuous operation of the wind tunnel at speeds of 250 fps, which is 2.5 times those of common university wind tunnels, and two hours of operation at the maximum tunnel velocity of 550 fps. This new and unique facility will be dedicated to basic research at near-flight Reynolds numbers, thereby, aiding in the design of the next generation of aircraft. The equipment acquired under this Grant has made many of these objectives become realities. Keywords: Laser doppler anemometer, Data acquisition. (edc)
Management and Control of Separation by Unsteady and Vortical Flows( Book )

1 edition published in 1988 in English and held by 1 WorldCat member library worldwide

Management and Control of two-and three-dimensional separated flows by unsteady and/or vortical flows is investigated in a number of configurations aimed at an enhanced basic understanding of governing mechanisms. The investigations are aimed at impacting the design of future generations of aircraft with improved maneuverability for better performance and safety. Also, novel techniques are being developed for the measurement, mapping and documentation of these complex unsteady flowfields. Keywords: Separation, Unsteady flows, Vortical flows. (MJM)
Investigation of Turbulent Boundary Layers Subjected to Internally or Externally Imposed Time-Dependent Transverse Shear( Book )

2 editions published in 1997 in English and held by 1 WorldCat member library worldwide

Both experimental and modeling efforts are aimed at understanding the non-equilibrium effects introduced by a 2-D turbulent boundary layer suddenly subjected to transverse wall shear. A new turbulence model has been developed which can be used to predict the Reynolds stress development in 3-D shear flows. This theta-l model allows for a misalignment to occur between the stress and strain as observed in 3-D turbulent boundary layers. The misalignment is determined by accounting for the flow history through solving a transport equation (first derived by Bradshaw, 1971) for theta. Excellent agreement is observed for both mean profiles and Reynolds stress when compared with the experiments of Driver and Johnston (1990). For the experiments, a 36' long 18" diameter cylinder surface is used. One section of the model is designed to rotate about its axis; thereby, introducing non-equilibrium effects into the developing 2-D boundary layer. Stereoscopic PIV is being used to acquire all three components of the velocity in both the x-y and x-z planes. Comparison of the detailed experimental results with subsequent modifications of the modeling should result in improved non-equilibrium turbulence prediction capabilities
The National Diagnostic Facility under Construction( Book )

1 edition published in 1988 in English and held by 1 WorldCat member library worldwide

The ITT Fluid Dynamics Research Center is nearing completion on the construction of a flexible diagnostic wind tunnel. This national facility will become a center for research at the university level on active and passive flow management of turbulent, unsteady and three-dimensional aerodynamics at high subsonic speeds. This unique wind tunnel will fill a serious void between other current basis research facilities in this country, and its use will be open to university, government and industry scientists. The facility is designed to operate at velocities up to 500 ft/sec in a test section of 4 ft by 5 ft cross section by 40 ft long. All operations of this facility, including optimum free-spectrum settings, unsteady flow operation, cooling of the tunnel air, the positioning and motion of aerodynamic models, the setting of streamwise pressure gradient as well as three-dimensional motions of traversing mechanisms and model positions, will be controlled by digital computers. (jes)
Closed-Loop Control of Acoustic Tones in Aircraft Cavities( )

1 edition published in 2002 in English and held by 0 WorldCat member libraries worldwide

An experimental investigation of acoustic mode noise suppression was conducted with a cavity model at the U.S. Air Force Academy Subsonic Wind Tunnel. Analog and digital control systems were used to suppress Rossiter tones over the Mach number range 0.25 to 0.5. The effectiveness of different closed-loop control strategies was investigated, including PD type, adaptive and a flow physics based algorithm. Experiments showed the Rossiter modes to have either a strong single-mode character or weak multimode character depending upon Mach number
A PIV System for Time-Resolved Measurements at High Reynolds Numbers in the National Diagnostic Facility( )

1 edition published in 1997 in English and held by 0 WorldCat member libraries worldwide

The necessary equipment for a two camera DPIV system was purchased. It included two cameras, two frame grabbers, a PC based computer, a laser and shutter, optics for the camera, optics for the laser, a workstation for computational processing, and control and signal conditioning electronics. A unique feature of this system is the utilization of special cameras which allow externally synchronized acquisition of two frames separated by only 1- 5 microns, permitting cross-correlation PIV analysis for flows up to 250 m/s. The DPIV system has been put together and tested in the Mark V Morkovin wind tunnel at IIT. Comparison between the statistics of the resulting velocity field and earlier hot-wire measurements in the same wind tunnel reveals the ability of the new DPIV system to provide high spatial resolution measurements with high accuracy. The new system is currently being adapted for use in the National Diagnostic Facility (NDF) at IIT
Interactive Control in Turbulent Shear Layers( )

2 editions published between 1992 and 1993 in English and held by 0 WorldCat member libraries worldwide

Using Particle Image Velocimetry in a turbulent pipe flow, instantaneous large-scale structures were observed, which are not seen in low Reynolds number direct numerical simulations of bounded turbulent shear flow. A probable explanation for this discrepancy is the much larger experimental Reynolds number as compared with the DNS results. Further support of this Reynolds number influence was found when quantifying the relative role of the outer-layer structures and wall-layer structures on the spanwise correlation coefficient between the wall-shear stress and streamwise velocity. That is, the results suggest that the influence of the outer flow on the streamwise velocity fluctuations at y+ = 10, increases with increasing Reynolds number. This outer-layer effect was then further examined in terms of the boundary layer intermittency/wall-layer dynamics coupling. Although the outer layer is directly influencing the wall-layer region, it was found that the alternating passages of laminar and turbulent regions in the intermittent part o the boundary layer were not directly influencing the buffer layer statistics. The mechanisms of this influence are currently being investigated
Instantaneous Velocity and Wall Pressure Features in a Turbulent Boundary Layer( )

1 edition published in 1997 in English and held by 0 WorldCat member libraries worldwide

Instantaneous organized motions in a turbulent boundary layer are related to characteristic wall pressure signatures for 1500 <Re(theta) <6000 and are compared with structures extracted from conditional averaging. The conditional velocity and pressure fields were obtained from velocity measurements performed at 176 separate locations in the streamwise-wall normal plane, and from one microphone mounted flush with the boundary layer test plate. Instantaneous realizations of the velocity and pressure field were obtained through high-resolution particle image velocimetry and an array of 39 microphones. The instantaneous and conditional flow fields showed that an adverse pressure gradient associated with a positive wall pressure was present beneath a large-scale shear layer structure separating high speed flow upstream from low speed flow (du'/dx<0). Only the instantaneous measurements showed that an isolated negative wall pressure was associated with a shear layer of positive du'/dx denoted here as an 'inverse' shear layer; the structure was washed out and therefore not observed in the conditional averaging calculations. The shear layer exhibited large vorticity with the same sense of rotation as the mean vorticity and localized regions of strong turbulence production along the interface, whereas the inverse shear layer did not
Investigation of the Physics of Screech in Supersonic Jets and Turbulent Boundary Layers at High Reynolds Number and Control of Separation Through Oscillatory Blowing( )

1 edition published in 1996 in English and held by 0 WorldCat member libraries worldwide

Using a flapped NACA 0015 airfoil, measurements of static pressure and lift, with and without oscillatory forcing from the leading edge and flap, demonstrated effective separation control and lift enhancement over the range 0.1<M<0.4. Measurements showed that the lift increment was sensitive to the dimensionless forcing frequency. Additionally, a suction pressure coefficient of nearly -5.0 was produced on a previously stalled airfoil at M=0.4, indicating a region of supercritical flow on the airfoil, and suggesting that oscillatory blowing is a viable separation-control technique under compressible flow conditions. Using both the NDF test-section floor boundary layer and a suspended axisymmetric body, a range of momentum thickness Reynolds numbers of 7000<Re<50000 was investigated with a hot-wire anemometer. Streamwise mean and rms velocity and spectra in these boundary layers showed good agreement with established scaling observations. An increasing separation of scales and the appearance of a second low-frequency spectral peak were observed indicating a clear discrimination between inner and outer scales at high Reynolds number. Although some dependence on both axial and momentum thickness Reynolds number was observed, there appeared to be a linear relationship between friction velocity and free-stream velocity over this wide range of Reynolds numbers
Investigation of Incipient Dynamic Stall at High Reynolds Numbers( )

1 edition published in 2000 in English and held by 0 WorldCat member libraries worldwide

In the first part of this study, surface shear-stress measurements were obtained on a NACA 0012 airfoil model, undergoing a pitch-up motion from 0 deg to 43 deg angle of attack at a constant rate using an array of surface-mounted hot-film sensors. Dominant features in these data and in the standard deviations computed from these data were examined and related to events in the development and evolution of the unsteady separation over the suction surface. Results were compared with well-known features of the dynamic stall process seen in the surface-pressure distributions. Trends in the behavior of these features are presented for a range of non-dimensional pitch rates and chord Reynolds numbers. Significant changes were seen in the behavior of these features at high Reynolds numbers. The results suggest that these changes are due to transition in the shear layer at high pitch rates and quasi-steady behavior at low pitch rates. In the second pan of this study, large amplitude sinusoidal motions were investigated for a wide range of Reynolds numbers and reduced frequencies. A combination of unsteady pressure and shear-stress data at the surface of the airfoil provided detailed information about the development and evolution of the flowfield. In particular, the formation of the dynamic stall vortex (DSV) during the upstroke of the motion profile was examined in detail as well as the reattachment process during the downstroke of the motion profile. Significant changes in behavior were seen with changing Reynolds number, reduced frequency, and amplitude of oscillation. The mean angle did not affect the development of the DSV except at the highest reduced frequency (k=0.4). Amplitude of oscillation did not affect the development of the reattachment process
Closed-Loop Control Systems for Unsteady Forebodies and Three-Dimensional Pitching Airfoils at High Reynolds Number( )

1 edition published in 1995 in English and held by 0 WorldCat member libraries worldwide

Progress made on closed loop control systems with application to aircraft forebodies and pitching airfoils is described in this report. The three main areas of the investigation included: (1) development of suitable control law algorithms for control of pitching wings and forebodies, (2) vorticity control on three-dimensional swept wings at high angles of attack, and (3) vortex control on forebody models at high angles of attack with unsteady motions. The three areas were investigated in parallel by laboratory experiment and numerical simulations. The numerical simulations examined the ability of distributed suction to control the flow over an airfoil undergoing a pitch-up motion and sinusoidal oscillation. Experiments on the feasibility of controlling dynamic stall using leading-edge suction were conducted. By studying the influence of different parameters such as pitch rate, Reynolds number, suction timing, suction slot size and location, a scaling law for the suction flow rate was developed. The third area of. investigation involved closed-loop control of forebody flow vortex asymmetry. By incorporating a closed- loop system, the desired side force could be maintained under a variety of different pitching. The relative performance of linear, nonlinear and neural network control algorithms was explored
Study of the Coupling Between Twin Single Beveled Supersonic Jets Using Linear and Non-Linear Spectral Analysis Techniques( )

1 edition published in 2004 in English and held by 0 WorldCat member libraries worldwide

Twin jets emanating from closely spaced nozzles can interact quite unpredictably and give rise to high dynamic pressures in the internozzle region which can result in sonic fatigue of sensitive aircraft equipment. This project studies the interaction between two such jet from nozzles having a single beveled exit geometry. Such nozzles are finding increasing use in modern aircraft due to the thrust vectoring and performance advantages they present. The study begins by using traditional linear spectral analysis techniques to study the coupling mechanism. It goes on to reveal the limitations of such linear techniques for understanding phenomena that are as complex as the one studied in this project and uses non-linear techniques to uncover results that have hitherto gone unreported. It is hoped that the results of these techniques will be of use to nozzle designers as well as to scientists involved in the field of numerical simulation of jet noise so as to provide benchmark data for the validation of their models
Control and Management of Unsteady and Turbulent Flows( )

1 edition published in 1993 in English and held by 0 WorldCat member libraries worldwide

Active input of tuned and detuned two-dimensional and oblique modes in a layer was found to lead to the growth of near-subharmonic modes as well as numerous sum and difference modes, thereby emulating 'natural' transition. Acoustic receptivity of laminar boundary layers with nonlocalized low-amplitude periodic waviness was experimentally investigated and compared favorably to theoretical predictions. Closed loop excitation of axisymmetric and azimuthal modes in a free round jet were used to reveal the character of high Reynolds number transition (i.e., supercritical Hopf bifurcation) and to study mode selection and switching. Suction and blowing were shown to be capable of controlling the asymmetric flow about the forebodies of aircraft and missiles and the experiments indicate that the suction bleed coefficient must increase like the 3.9 power of the velocity to balance the effects of geometric instability at the tip. The effects of yaw on such asymmetries were also documented. A strategy to suppress the dynamic-stall vortex over a range of operating parameters, using controlled leading-edge suction to prevent accumulation of reverse-flowing fluid, was successfully developed from a study of the mechanisms responsible for the evolution of the vortex. The National Diagnostic Facility was completed and several collaborative experiments are scheduled during 1994. Turbulence, Separated flows, Unsteady flows, Transition, Forebody flows, Pitching airfoils, Jet flows, Control
Asymmetric Vortical Flows Over Slender Bodies with Appendages( )

1 edition published in 1994 in English and held by 0 WorldCat member libraries worldwide

In part one of this study, the interaction between vortices forming at the tip of a missile model, and a single fin located down the axis of the model was investigated experimentally for a range of axial fin position azimuthal fin positions and Reynolds number for two angles of attack. Symmetric, attached vortices formed over the model for the first angle of attack, while the vortex system was asymmetric for the second. The interaction was documented using flow visualization and mean-pressure measurements on the fin surfaces. The pressure data were used to compute the normal-force efficients on the fin. The effects of the interaction on the fin are described. Results include a detailed examination of the fin interaction with the symmetric and asymmetric vortex systems, the azimuthal range of fin positions over which interaction occurs, and the effects interaction on the fin are described. Results include a detailed examination of the fin interaction with the symmetric and asymmetric vortex systems, the azimuthal range of fin positions over which interaction occurs, and the effects of changing axial fin location and Reynolds number. In the second part, the vortical flow over a steady missile configuration with a tangent-ogive forebody was investigated for different angles of attack. The model was designed in a such a way to allow the tip and the aft body to be stationary and the body to roll. This enabled measurement of the pressure over the model surface without disturbing the flow field. The angle of attack and Reynolds number were varied from 0 degrees to 85 degrees and from 6000 to 34000, respectively. Flow visualization and pressure distributions acquired at several azimuthal angles were used to describe the flow regions and the onset of asymmetry
Application of Micro Electro-Mechanical Sensors and Activators in the Investigation of Supersonic Jet Screech( )

1 edition published in 1997 in English and held by 0 WorldCat member libraries worldwide

An investigation aimed at examining the usability of MEMS based actuators for controlling supersonic jet screech has been conducted. First, documentation of the screech phenomenon in the newly constructed high speed jet facility (HSJF) at IIT has been completed. Results from microphone measurements complemented with earlier shadowgraph and schlieren visualization have shown that the screech characteristics in the HSJF conforms with that published in the literature. Second, detailed investigation of the first generation MEMS actuators showed that the actuators could not operate for speeds higher than 70 m/s while maintaining contact with the jet shear layer. This was attributed to the bending moment acting on the actuator due to flow loading on the overhanging head portion of the device. This observation was confirmed utilizing a special headless actuator design. The outcome of the tests of the first generation devices guided the development of a second generation of actuators. Those actuators, which are also described within this report, are currently being evaluated
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