The leading-edge receptivity to acoustic waves of two-dimensional bodies is investigated using a ... more The leading-edge receptivity to acoustic waves of two-dimensional bodies is investigated using a spatial solution of the Navier–Stokes equations in vorticity/stream function form in general curvilinear coordinates. The free stream is composed of a uniform flow with a superposed periodic velocity fluctuation of small amplitude. The method follows that of Haddad & Corke (1998), in which the solution for the basic flow and the linearized perturbation flow are solved separately. The initial motivation for the work comes from past physical experiments for flat plates with elliptic leading edges, which indicated narrow frequency bands of higher neutral-curve Branch I receptivity. We investigate the same conditions in our simulations, as well as on a parabolic leading edge. The results document the importance of the leading edge, junction between the ellipse and flat plate, and pressure gradient to the receptivity coefficient at Branch I. Comparisons to the past experiments and other numer...
ABSTRACT The results of a numerical simulation and experiment characterizing the performance of p... more ABSTRACT The results of a numerical simulation and experiment characterizing the performance of plasma streamwise vortex generators in controlling separation and secondary flow within a serpentine, diffusing duct are presented. A no flow control case is first run to check agreement of location of separation, development of secondary flow, and total pressure recovery between the experiment and numerical results. Upon validation, passive vane-type vortex generators and plasma streamwise vortex generators are implemented to increase total pressure recovery and reduce flow distortion at the aerodynamic interface plane: the exit of the S-duct. Total pressure recovery is found experimentally with a pitot probe rake assembly at the aerodynamic interface plane. Stagnation pressure distortion descriptors are also presented to show the performance increase with plasma streamwise vortex generators in comparison to the baseline no flow control case. These performance parameters show that streamwise plasma vortex generators are an effective alternative to vane-type vortex generators in total pressure recovery and total pressure distortion reduction in S-duct inlets.
50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2012
ABSTRACT Wind tunnel experiments were conducted to quantify the effectiveness of alternating curr... more ABSTRACT Wind tunnel experiments were conducted to quantify the effectiveness of alternating current dielectric barrier discharge flow control actuators to suppress leading-edge stall on a NASA energy efficient transport airfoil at compressible freestream speeds. The objective of this research was to increase lift, reduce drag, and improve the stall characteristics of the supercritical airfoil near stall by flow reattachment at relatively high Mach and Reynolds numbers. In addition, the effect of unsteady (or duty cycle) operation on these aerodynamic quantities was also investigated. The experiments were conducted for a range of Mach numbers between 0.1 and 0.4. corresponding to a Reynolds number range of 560,000 through 2,260,000. Lift, drag, quarter chord moment, and suction side pressures were measured near stall for baseline, steady actuation, and a scan of nondimensional duty cycle frequencies. The results show that the plasma actuators were effective at reattaching the leading-edge separated flow as evidenced by the increase in maximum lift coefficient and stall angle (as much as 2.5 degrees). The experiment also showed that lift was increased the most when the plasma actuator was operated unsteady with a nondimensional frequency of unity.
The determination of pressures along the surface of a wind tunnel proves difficult with methods t... more The determination of pressures along the surface of a wind tunnel proves difficult with methods that must introduce devices into the flow stream. In this investigation, an optical pressure sensor is presented that is part of the wall and measures the wall pressure fluctuations without disturbing the flow. A special interferometric reflection moire technique is developed and used to produce slope fringes. A CCD camera with a speed of 60 Hz records instantaneous pattern of the slope fringes. A neural network is then used to analyze the fringe patterns and classify the pressures into five levels. A second neural network is used to recognize the pressure patterns and to provide the input to a control system that is capable of modifying the shape of a flexible wall located in the upstream of the flow and preserve the stability of the flow. Pressure measurements are done with air flowing at a speed of 6.2m / sec in the wind tunnel and at various mode forcing conditions. Pressures measured...
Flow control to avoid or delay rotorcraft retreating blade stall can be an enabling technology fo... more Flow control to avoid or delay rotorcraft retreating blade stall can be an enabling technology for future high performance rotorcraft. Aerodynamic experiments and computations have indicated that appropriate unsteady excitation can delay boundary layer separation and stall on airfoils. Work is in progress to determine the control requirements for helicopter rotor blades at full scale Mach numbers, Reynolds numbers, and with unsteady pitching motions. Compact, powerful, and efficient flow actuation and control systems will be needed. Three actuation concepts were favorably evaluated during initial studies: electromechanical directed synthetic jets (DSJ), periodic flow modulation, and plasma actuation. Electromechanical DSJ and plasma actuators are being developed further and will be evaluated in full scale pitching blade section experiments. These experiments will determine the required control authority, validate the actuator concepts, and study open and closed loop control approaches. Computational studies are being performed of the combined external and actuator flow fields to determine preferred actuation geometries and operating points. System analyses are being used to quantify the benefits for representative aircraft configurations and missions.
44th AIAA Aerospace Sciences Meeting and Exhibit, 2006
The aerodynamic plasma actuator has shown considerable promise as a o w control device in dieren ... more The aerodynamic plasma actuator has shown considerable promise as a o w control device in dieren t applications. It has been shown previously that the lumped-element circuit model correctly describes the behavior of the aerodynamic plasma actuator. To incorporate this model into the Navier-Stokes solver, it was modied to include the spatial distribution of the discharge within the plasma. To model the behavior of the single dielectric barrier discharge aerodynamic plasma actuator, we represent it as a network of electric circuit elements. The electric circuit consists of N elementary subcircuits, each representing a small physical domain with nite width and length. Each subcircuit consists of the air capacitor, dielectric capacitor, plasma resistive element, and diodes which govern the presence of the plasma. The results of the simulation are compared to the experimental data of the plasma spatial distribution obtained with a photomultiplier tube.
A linear cascade that is designed to simulate the flow around blades in the low-pressure turbine ... more A linear cascade that is designed to simulate the flow around blades in the low-pressure turbine stage of turbo-jet engines is used to study the physics of the tip-gap flow and vortex. The cascade consists of three Pratt \& Whitney ``PakB'' blades. The experiment investigated gap sizes ...
A high-speed linear cascade is used to investigate passive and active approaches for controlling ... more A high-speed linear cascade is used to investigate passive and active approaches for controlling the over-tip leakage flow associated with the turbine blades in the low-pressure stage of a gas turbine engine. The cascade consists of Pratt \& Whitney ``PakB'' blades with varying gap ...
The single dielectric barrier discharge plasma, a plasma sustainable at atmospheric pressure, has... more The single dielectric barrier discharge plasma, a plasma sustainable at atmospheric pressure, has shown considerable promise as a flow control device operating at modest (tens of watts) power levels. Measurements are presented of the development of the plasma during the course of the discharge cycle, and the relevance of these measurements to the modeling of the actuator's electrical properties is discussed. Experimental evidence is presented strongly pointing to the electric field enhancement near the leading edge of the actuator as a dominant factor determining the effectiveness of momentum coupling into the surrounding air
Entropy in information theory is defined as the expected or mean value of the measure of the amou... more Entropy in information theory is defined as the expected or mean value of the measure of the amount of self-information contained in the ith point of a distribution series x sub i, based on its probability of occurrence p(x sub i). If p(x sub i) is the probability of the ith state of the system in probability space, then the entropy, E(X) = - sigma p(x sub i) logp (x sub i), is a measure of the disorder in the system. Based on this concept, a method was devised which sought to minimize the entropy in a time series in order to construct the signature of the most coherent motions. The constrained minimization was performed using a Lagrange multiplier approach which resulted in the solution of a simultaneous set of non-linear coupled equations to obtain the coherent time series. The application of the method to space-time data taken by a rake of sensors in the near-wall region of a turbulent boundary layer was presented. The results yielded coherent velocity motions made up of locally decelerated or accelerated fluid having a streamwise scale of approximately 100 nu/u(tau), which is in qualitative agreement with the results from other less objective discrimination methods.
The Police Journal: Theory, Practice and Principles
Bullet-resistant body armour is used by law enforcement agencies and military personnel worldwide... more Bullet-resistant body armour is used by law enforcement agencies and military personnel worldwide, often in inclement weather. Some fibre types used in body armour perform poorly when wet, resulting in a reduced level of protection; this is why most body armour protective elements are water-repellent treated and/or protected by a water-resistant cover. Some of the users operate in the maritime environment. The effect of salt water on body armour performance has not been previously reported. In this work the effect of soaking body armour in salt water and exposing body armour for up to 10 soaking and drying cycles in salt water was investigated. The effectiveness of the water-resistant cover was investigated by considering three cover conditions: (i) intact, (ii) cut and (iii) removed. Wet armour was heavier and provided significantly less protection from 9 mm Luger FMJ ammunition when compared to not-exposed armour irrespective of cover condition. A degradation in performance of arm...
Proceedings of the Dynamic Flow Conference 1978 on Dynamic Measurements in Unsteady Flows, 1978
... Recently smoke wire visualization records have been studied with the aid of digital image pro... more ... Recently smoke wire visualization records have been studied with the aid of digital image processing. ... typical processing of the photographs includes multiple image averaging, thresholding, edge and texture detection, streakline following and spectral analysis of the ...
The leading-edge receptivity to acoustic waves of two-dimensional bodies is investigated using a ... more The leading-edge receptivity to acoustic waves of two-dimensional bodies is investigated using a spatial solution of the Navier–Stokes equations in vorticity/stream function form in general curvilinear coordinates. The free stream is composed of a uniform flow with a superposed periodic velocity fluctuation of small amplitude. The method follows that of Haddad & Corke (1998), in which the solution for the basic flow and the linearized perturbation flow are solved separately. The initial motivation for the work comes from past physical experiments for flat plates with elliptic leading edges, which indicated narrow frequency bands of higher neutral-curve Branch I receptivity. We investigate the same conditions in our simulations, as well as on a parabolic leading edge. The results document the importance of the leading edge, junction between the ellipse and flat plate, and pressure gradient to the receptivity coefficient at Branch I. Comparisons to the past experiments and other numer...
ABSTRACT The results of a numerical simulation and experiment characterizing the performance of p... more ABSTRACT The results of a numerical simulation and experiment characterizing the performance of plasma streamwise vortex generators in controlling separation and secondary flow within a serpentine, diffusing duct are presented. A no flow control case is first run to check agreement of location of separation, development of secondary flow, and total pressure recovery between the experiment and numerical results. Upon validation, passive vane-type vortex generators and plasma streamwise vortex generators are implemented to increase total pressure recovery and reduce flow distortion at the aerodynamic interface plane: the exit of the S-duct. Total pressure recovery is found experimentally with a pitot probe rake assembly at the aerodynamic interface plane. Stagnation pressure distortion descriptors are also presented to show the performance increase with plasma streamwise vortex generators in comparison to the baseline no flow control case. These performance parameters show that streamwise plasma vortex generators are an effective alternative to vane-type vortex generators in total pressure recovery and total pressure distortion reduction in S-duct inlets.
50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2012
ABSTRACT Wind tunnel experiments were conducted to quantify the effectiveness of alternating curr... more ABSTRACT Wind tunnel experiments were conducted to quantify the effectiveness of alternating current dielectric barrier discharge flow control actuators to suppress leading-edge stall on a NASA energy efficient transport airfoil at compressible freestream speeds. The objective of this research was to increase lift, reduce drag, and improve the stall characteristics of the supercritical airfoil near stall by flow reattachment at relatively high Mach and Reynolds numbers. In addition, the effect of unsteady (or duty cycle) operation on these aerodynamic quantities was also investigated. The experiments were conducted for a range of Mach numbers between 0.1 and 0.4. corresponding to a Reynolds number range of 560,000 through 2,260,000. Lift, drag, quarter chord moment, and suction side pressures were measured near stall for baseline, steady actuation, and a scan of nondimensional duty cycle frequencies. The results show that the plasma actuators were effective at reattaching the leading-edge separated flow as evidenced by the increase in maximum lift coefficient and stall angle (as much as 2.5 degrees). The experiment also showed that lift was increased the most when the plasma actuator was operated unsteady with a nondimensional frequency of unity.
The determination of pressures along the surface of a wind tunnel proves difficult with methods t... more The determination of pressures along the surface of a wind tunnel proves difficult with methods that must introduce devices into the flow stream. In this investigation, an optical pressure sensor is presented that is part of the wall and measures the wall pressure fluctuations without disturbing the flow. A special interferometric reflection moire technique is developed and used to produce slope fringes. A CCD camera with a speed of 60 Hz records instantaneous pattern of the slope fringes. A neural network is then used to analyze the fringe patterns and classify the pressures into five levels. A second neural network is used to recognize the pressure patterns and to provide the input to a control system that is capable of modifying the shape of a flexible wall located in the upstream of the flow and preserve the stability of the flow. Pressure measurements are done with air flowing at a speed of 6.2m / sec in the wind tunnel and at various mode forcing conditions. Pressures measured...
Flow control to avoid or delay rotorcraft retreating blade stall can be an enabling technology fo... more Flow control to avoid or delay rotorcraft retreating blade stall can be an enabling technology for future high performance rotorcraft. Aerodynamic experiments and computations have indicated that appropriate unsteady excitation can delay boundary layer separation and stall on airfoils. Work is in progress to determine the control requirements for helicopter rotor blades at full scale Mach numbers, Reynolds numbers, and with unsteady pitching motions. Compact, powerful, and efficient flow actuation and control systems will be needed. Three actuation concepts were favorably evaluated during initial studies: electromechanical directed synthetic jets (DSJ), periodic flow modulation, and plasma actuation. Electromechanical DSJ and plasma actuators are being developed further and will be evaluated in full scale pitching blade section experiments. These experiments will determine the required control authority, validate the actuator concepts, and study open and closed loop control approaches. Computational studies are being performed of the combined external and actuator flow fields to determine preferred actuation geometries and operating points. System analyses are being used to quantify the benefits for representative aircraft configurations and missions.
44th AIAA Aerospace Sciences Meeting and Exhibit, 2006
The aerodynamic plasma actuator has shown considerable promise as a o w control device in dieren ... more The aerodynamic plasma actuator has shown considerable promise as a o w control device in dieren t applications. It has been shown previously that the lumped-element circuit model correctly describes the behavior of the aerodynamic plasma actuator. To incorporate this model into the Navier-Stokes solver, it was modied to include the spatial distribution of the discharge within the plasma. To model the behavior of the single dielectric barrier discharge aerodynamic plasma actuator, we represent it as a network of electric circuit elements. The electric circuit consists of N elementary subcircuits, each representing a small physical domain with nite width and length. Each subcircuit consists of the air capacitor, dielectric capacitor, plasma resistive element, and diodes which govern the presence of the plasma. The results of the simulation are compared to the experimental data of the plasma spatial distribution obtained with a photomultiplier tube.
A linear cascade that is designed to simulate the flow around blades in the low-pressure turbine ... more A linear cascade that is designed to simulate the flow around blades in the low-pressure turbine stage of turbo-jet engines is used to study the physics of the tip-gap flow and vortex. The cascade consists of three Pratt \& Whitney ``PakB'' blades. The experiment investigated gap sizes ...
A high-speed linear cascade is used to investigate passive and active approaches for controlling ... more A high-speed linear cascade is used to investigate passive and active approaches for controlling the over-tip leakage flow associated with the turbine blades in the low-pressure stage of a gas turbine engine. The cascade consists of Pratt \& Whitney ``PakB'' blades with varying gap ...
The single dielectric barrier discharge plasma, a plasma sustainable at atmospheric pressure, has... more The single dielectric barrier discharge plasma, a plasma sustainable at atmospheric pressure, has shown considerable promise as a flow control device operating at modest (tens of watts) power levels. Measurements are presented of the development of the plasma during the course of the discharge cycle, and the relevance of these measurements to the modeling of the actuator's electrical properties is discussed. Experimental evidence is presented strongly pointing to the electric field enhancement near the leading edge of the actuator as a dominant factor determining the effectiveness of momentum coupling into the surrounding air
Entropy in information theory is defined as the expected or mean value of the measure of the amou... more Entropy in information theory is defined as the expected or mean value of the measure of the amount of self-information contained in the ith point of a distribution series x sub i, based on its probability of occurrence p(x sub i). If p(x sub i) is the probability of the ith state of the system in probability space, then the entropy, E(X) = - sigma p(x sub i) logp (x sub i), is a measure of the disorder in the system. Based on this concept, a method was devised which sought to minimize the entropy in a time series in order to construct the signature of the most coherent motions. The constrained minimization was performed using a Lagrange multiplier approach which resulted in the solution of a simultaneous set of non-linear coupled equations to obtain the coherent time series. The application of the method to space-time data taken by a rake of sensors in the near-wall region of a turbulent boundary layer was presented. The results yielded coherent velocity motions made up of locally decelerated or accelerated fluid having a streamwise scale of approximately 100 nu/u(tau), which is in qualitative agreement with the results from other less objective discrimination methods.
The Police Journal: Theory, Practice and Principles
Bullet-resistant body armour is used by law enforcement agencies and military personnel worldwide... more Bullet-resistant body armour is used by law enforcement agencies and military personnel worldwide, often in inclement weather. Some fibre types used in body armour perform poorly when wet, resulting in a reduced level of protection; this is why most body armour protective elements are water-repellent treated and/or protected by a water-resistant cover. Some of the users operate in the maritime environment. The effect of salt water on body armour performance has not been previously reported. In this work the effect of soaking body armour in salt water and exposing body armour for up to 10 soaking and drying cycles in salt water was investigated. The effectiveness of the water-resistant cover was investigated by considering three cover conditions: (i) intact, (ii) cut and (iii) removed. Wet armour was heavier and provided significantly less protection from 9 mm Luger FMJ ammunition when compared to not-exposed armour irrespective of cover condition. A degradation in performance of arm...
Proceedings of the Dynamic Flow Conference 1978 on Dynamic Measurements in Unsteady Flows, 1978
... Recently smoke wire visualization records have been studied with the aid of digital image pro... more ... Recently smoke wire visualization records have been studied with the aid of digital image processing. ... typical processing of the photographs includes multiple image averaging, thresholding, edge and texture detection, streakline following and spectral analysis of the ...
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Papers by T. Corke