WorldCat Identities

Naguib, Ahmed

Overview
Works: 6 works in 7 publications in 1 language and 7 library holdings
Publication Timeline
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Most widely held works by Ahmed Naguib
A Doppler Sensor Array for High-Resolution Measurements of the Wavenumber-Frequency Spectrum of the Turbulent Wall Pressure at High Reynold Numbers( Book )

1 edition published in 2003 in English and held by 1 WorldCat member library worldwide

The Doppler frequency shift is utilized as the basic sensing mechanism for a new unsteady-surface pressure measurement technique. The frequency shift is experienced by a focused laser beam reflected off the aluminized top of a flexible-polymer diaphragm subjected to the unsteady pressure. Prototypical sensors based on this concept, with different sizes and diaphragm material and thickness are constructed as well as evaluated. The results provide understanding of the limits of the sensor's sensitivity, bandwidth, resolution and noise-level. Moreover, analysis of typical wall-pressure spectra beneath high- and low-Reynolds-number, boundary layers in light of these limits underlines the potential advantage of the new sensor in resolving the signature of small-scale turbulent structures at high Reynolds numbers
Active Control of Supersonic Jet Screech Using MEMS( Book )

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

The primary objective of this research is to investigate the usability of mechanical actuators, manufactured using MEMS technology, in the control of high-speed, compressible free shear flows. Appropriate development of MEMS-based actuators for flow control applications must address two issues: (1) the ability of the micron-size amplitude and forces of the MEMS devices to affect larger-scale flows with orders of magnitude higher energy, and (2) the survivability of the fairly fragile actuators when they are exposed to the flow in which they are embedded. Therefore, the current investigation is aimed at testing MEMS actuators for the purpose of controlling supersonic jet screech. For this application, the high-speed, highly-unsteady nature of the flow during screech provides a reasonably harsh environment for testing the survivability of the actuators. Furthermore, the shear layer surrounding the jet at its exit is known to be highly unstable to minute disturbances in the vicinity of the lip of the jet, and hence it is anticipated that the micron-size disturbances introduced by the MEMS actuators will be amplified through the shear layer instability mechanisms to produce large scale effects on the jet itself
Wall shear stress( Book )

1 edition published in 2013 in English and held by 1 WorldCat member library worldwide

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
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
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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Audience level: 0.93 (from 0.90 for Wall shear ... to 0.99 for Investigat ...)

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