Counts Energy (keV) 55 Fe Spectrum With Si-PIN for X-Ray Detection XR-100CR 5.9 keV Energy (keV) ... more Counts Energy (keV) 55 Fe Spectrum With Si-PIN for X-Ray Detection XR-100CR 5.9 keV Energy (keV) Counts 57 Co Spectrum 530 eV FWHM 850 eV FWHM 122 keV With Cadmium Telluride (CdTe) for γ-Ray Detection
Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 q... more Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 quiet wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle image velocimetry. It is found that the second instability acoustic mode is the key modulator of the transition process. The second mode experiences a rapid growth and a very fast annihilation due to the effect of bulk viscosity. The second mode interacts strongly with the first vorticity mode to directly promote a fast growth of the latter and leads to immediate transition to turbulence.
The earth's desert boundary layer is modeled in a wind tunnel. Velocity profile measurcments are ... more The earth's desert boundary layer is modeled in a wind tunnel. Velocity profile measurcments are determined on and around a barchan dune model inserted in the roughness layer on the tunnel floor. A theoretical investigation is made into •che factors influencing the rate of sand flow around the dune. Flow visualization techniques are employed in the mapping of streamlines of flow on the dune's surface. Maps of erosion and deposition of sand are constructed for the barchan model, utilizing both flow visualization techniques and friction velocities calculated from the measured velocity profiles. The sediment budget found experimentally for the model is compared. to predicted and observed results reported by others. The comparison shows fairly good agreement between the experimentally determined and predicted sediment t budgets; this provides encouragement for the utilization of wind tunnel simulation and friction velocity approximation in determining erosion and deposition rates due to wind action.
Bulletin of the American Physical Society, Nov 21, 2011
present a numerical study aimed at investigating the influence of microstructural parameters on t... more present a numerical study aimed at investigating the influence of microstructural parameters on the resistance of submerged fibrous superhydrophobic coatings to elevated hydrostatic pressures. In particular, we generate 3-D virtual geometries comprised of randomly or orthogonally oriented horizontal fibers with bimodal diameter distributions resembling the microstructure of coatings produced via DC and AC electrospinning, respectively. These virtual geometries are then used as the computational domain for performing Full Morphology (FM) simulations to establish a relationship between the coatings' critical pressure-pressure beyond which the surface departs from the Cassie state-and their microstructures. Our numerical simulations are aimed at providing guidelines for the design and optimization of the coatings' microstructures.
Description/Abstract Laboratory experiments were conducted in a wind-wave tank to study the turbu... more Description/Abstract Laboratory experiments were conducted in a wind-wave tank to study the turbulent characteristics in the water boundary-layers under the action of wind and waves and to study the oil dispersion characteristics under the action of breaking waves. Effects of an oil slick on the wind-waves or mechanically-generated waves with wind were also investigated. The objective was to understand by means of laboratory experiments the behavior of oil dispersion in the upper ocean. Two new instruments, a laser Doppler ...
Two preliminary concepts of propulsion based on a bacterial flagellum motor (BFM) were developed ... more Two preliminary concepts of propulsion based on a bacterial flagellum motor (BFM) were developed with the potential for use in micro-air-vehicles (MAV). The first uses the conventional turbojet without the turbine with a BFM to run the compressor. The second concept uses the ...
Facets and scope of large-scale disasters are briefly discussed in this forum. A universal quanti... more Facets and scope of large-scale disasters are briefly discussed in this forum. A universal quantitative metric is proposed that puts all natural and human-derived disasters on a common scale. Issues of prediction, control, and mitigation of catastrophes are broadly introduced. The laws of nature govern the evolution of any disaster. In some cases, as for example weather-related disasters, those first-principles laws could be written in the form of field equations, but exact solutions of these often nonlinear differential equations are impossible to obtain, particularly for turbulent flows; heuristic models together with intensive use of supercomputers are necessary to proceed. In other cases, as for example earthquakes, the precise laws are not even known and prediction becomes somewhat problematic. Management of any type of disaster is more art than science. Nevertheless, much can be done by both social and physical scientists/engineers to alleviate the resulting pain and suffering.
Manufacturing processes that can create extremely small machines have been developed in recent ye... more Manufacturing processes that can create extremely small machines have been developed in recent years. Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 micron, that combine electrical and ...
Among the modem goals of external flow control are separation postponement, lift enhancement, tra... more Among the modem goals of external flow control are separation postponement, lift enhancement, transition delay or advancement, and drag reduction. These objectives are not necessarily mutually exclusive. For low-Reynolds-number lifting surfaces, where the formation of a laminar separation bubble may have a dominant effect on the flow field, the interrelation between the above goals is particularly salient, presenting an additional degree of complexity. The present article is an overview of passive and active techniques used to control a low-Reynolds-number boundary layer to achieve an improved performance. A unified view based on a vorticity framework will be presented to explain many of the available or contemplated control methods. Among the control techniques to be considered are wall suction/injection, shaping, heat transfer through the surface, introduction of a foreign substance into the boundary layer, fixed or moving geometric modifications, and turbulence manipulation. Among the practical considerations that will be reviewed for these devices are their cost of construction and operation, complexity, and potential trade-off’s or penalties associated with their use.
Abstract The ability to actively or passively manipulate a flow field to effect a desired change ... more Abstract The ability to actively or passively manipulate a flow field to effect a desired change is of immense technological importance. In this article, methods of control to achieve transition delay, separation postponement, lift enhancement, drag reduction, turbulence ...
Counts Energy (keV) 55 Fe Spectrum With Si-PIN for X-Ray Detection XR-100CR 5.9 keV Energy (keV) ... more Counts Energy (keV) 55 Fe Spectrum With Si-PIN for X-Ray Detection XR-100CR 5.9 keV Energy (keV) Counts 57 Co Spectrum 530 eV FWHM 850 eV FWHM 122 keV With Cadmium Telluride (CdTe) for γ-Ray Detection
Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 q... more Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 quiet wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle image velocimetry. It is found that the second instability acoustic mode is the key modulator of the transition process. The second mode experiences a rapid growth and a very fast annihilation due to the effect of bulk viscosity. The second mode interacts strongly with the first vorticity mode to directly promote a fast growth of the latter and leads to immediate transition to turbulence.
The earth's desert boundary layer is modeled in a wind tunnel. Velocity profile measurcments are ... more The earth's desert boundary layer is modeled in a wind tunnel. Velocity profile measurcments are determined on and around a barchan dune model inserted in the roughness layer on the tunnel floor. A theoretical investigation is made into •che factors influencing the rate of sand flow around the dune. Flow visualization techniques are employed in the mapping of streamlines of flow on the dune's surface. Maps of erosion and deposition of sand are constructed for the barchan model, utilizing both flow visualization techniques and friction velocities calculated from the measured velocity profiles. The sediment budget found experimentally for the model is compared. to predicted and observed results reported by others. The comparison shows fairly good agreement between the experimentally determined and predicted sediment t budgets; this provides encouragement for the utilization of wind tunnel simulation and friction velocity approximation in determining erosion and deposition rates due to wind action.
Bulletin of the American Physical Society, Nov 21, 2011
present a numerical study aimed at investigating the influence of microstructural parameters on t... more present a numerical study aimed at investigating the influence of microstructural parameters on the resistance of submerged fibrous superhydrophobic coatings to elevated hydrostatic pressures. In particular, we generate 3-D virtual geometries comprised of randomly or orthogonally oriented horizontal fibers with bimodal diameter distributions resembling the microstructure of coatings produced via DC and AC electrospinning, respectively. These virtual geometries are then used as the computational domain for performing Full Morphology (FM) simulations to establish a relationship between the coatings' critical pressure-pressure beyond which the surface departs from the Cassie state-and their microstructures. Our numerical simulations are aimed at providing guidelines for the design and optimization of the coatings' microstructures.
Description/Abstract Laboratory experiments were conducted in a wind-wave tank to study the turbu... more Description/Abstract Laboratory experiments were conducted in a wind-wave tank to study the turbulent characteristics in the water boundary-layers under the action of wind and waves and to study the oil dispersion characteristics under the action of breaking waves. Effects of an oil slick on the wind-waves or mechanically-generated waves with wind were also investigated. The objective was to understand by means of laboratory experiments the behavior of oil dispersion in the upper ocean. Two new instruments, a laser Doppler ...
Two preliminary concepts of propulsion based on a bacterial flagellum motor (BFM) were developed ... more Two preliminary concepts of propulsion based on a bacterial flagellum motor (BFM) were developed with the potential for use in micro-air-vehicles (MAV). The first uses the conventional turbojet without the turbine with a BFM to run the compressor. The second concept uses the ...
Facets and scope of large-scale disasters are briefly discussed in this forum. A universal quanti... more Facets and scope of large-scale disasters are briefly discussed in this forum. A universal quantitative metric is proposed that puts all natural and human-derived disasters on a common scale. Issues of prediction, control, and mitigation of catastrophes are broadly introduced. The laws of nature govern the evolution of any disaster. In some cases, as for example weather-related disasters, those first-principles laws could be written in the form of field equations, but exact solutions of these often nonlinear differential equations are impossible to obtain, particularly for turbulent flows; heuristic models together with intensive use of supercomputers are necessary to proceed. In other cases, as for example earthquakes, the precise laws are not even known and prediction becomes somewhat problematic. Management of any type of disaster is more art than science. Nevertheless, much can be done by both social and physical scientists/engineers to alleviate the resulting pain and suffering.
Manufacturing processes that can create extremely small machines have been developed in recent ye... more Manufacturing processes that can create extremely small machines have been developed in recent years. Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 micron, that combine electrical and ...
Among the modem goals of external flow control are separation postponement, lift enhancement, tra... more Among the modem goals of external flow control are separation postponement, lift enhancement, transition delay or advancement, and drag reduction. These objectives are not necessarily mutually exclusive. For low-Reynolds-number lifting surfaces, where the formation of a laminar separation bubble may have a dominant effect on the flow field, the interrelation between the above goals is particularly salient, presenting an additional degree of complexity. The present article is an overview of passive and active techniques used to control a low-Reynolds-number boundary layer to achieve an improved performance. A unified view based on a vorticity framework will be presented to explain many of the available or contemplated control methods. Among the control techniques to be considered are wall suction/injection, shaping, heat transfer through the surface, introduction of a foreign substance into the boundary layer, fixed or moving geometric modifications, and turbulence manipulation. Among the practical considerations that will be reviewed for these devices are their cost of construction and operation, complexity, and potential trade-off’s or penalties associated with their use.
Abstract The ability to actively or passively manipulate a flow field to effect a desired change ... more Abstract The ability to actively or passively manipulate a flow field to effect a desired change is of immense technological importance. In this article, methods of control to achieve transition delay, separation postponement, lift enhancement, drag reduction, turbulence ...
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