The Experts below are selected from a list of 117285 Experts worldwide ranked by ideXlab platform
Phillip J. Ansell - One of the best experts on this subject based on the ideXlab platform.
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Closed-loop trailing-edge separation Control system using empirical mode decomposition
AIAA Journal, 2018Co-Authors: Rohit Gupta, Phillip J. AnsellAbstract:Active unsteady flow Control experiments were performed on a natural laminar flow airfoil at Rec=1.0×106. The goal of this study was to Control Boundary-layer separation across the trailing-edge re...
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closed loop trailing edge separation Control system using empirical mode decomposition
AIAA Journal, 2018Co-Authors: Rohit Gupta, Phillip J. AnsellAbstract:Active unsteady flow Control experiments were performed on a natural laminar flow airfoil at Rec=1.0×106. The goal of this study was to Control Boundary-layer separation across the trailing-edge region of the airfoil in off-design conditions. Active Control of separation was achieved using a series of blowing slots at the x/c=0.75 location. An adaptive closed-loop Controller was developed based on the empirical mode decomposition algorithm. This Controller was capable of automatically identifying the frequencies of natural instabilities in the flowfield, which were then used to set the driving frequencies of the flow Control system. The airfoil performance with closed-loop frequency Control was compared against a canonical open loop F+=1 actuation. The differences in flowfield characteristics between these two cases were investigated in detail using particle image velocimetry measurements across the trailing-edge region of the airfoil. Closed-loop frequency Control was observed to be associated with more ...
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open loop and closed loop trailing edge separation Control on a natural laminar flow airfoil
54th AIAA Aerospace Sciences Meeting 2016, 2016Co-Authors: Rohit Gupta, Phillip J. AnsellAbstract:Active Unsteady Flow Control experiments were performed on a Natural Laminar Flow, NLF 0414 airfoil at Rec = 1.0 × 10 6 . The goal of this study was to Control Boundary-layer separation across the trailing-edge region of the airfoil in off-design conditions. Both openloop and closed-loop Control approaches were used. Active Control of separation was achieved using a series of blowing slots at the x/c = 0.75 location. Open loop Control parameters were varied across a parametric range of jet amplitudes, actuation frequencies and duty cycles and performance measurements were acquired to identify the effectiveness of these actuation schemes. PIV measurements were acquired across a horizontal plane near the trailing edge region of the model to understand the effects of actuation on flow separation and the vortex dynamics associated with unsteady actuation. A closed loop Controller was developed to vary the actuation parameters in-situ using sensory feedback from the unsteady surface pressure measurements and adaptive modal decomposition methods. This closed-loop system was able to automatically Control the extent of separation such that a desired value of Cl was obtained.
Ralph J Volino - One of the best experts on this subject based on the ideXlab platform.
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separation Control on low pressure turbine airfoils using synthetic vortex generator jets
Journal of Turbomachinery-transactions of The Asme, 2003Co-Authors: Ralph J VolinoAbstract:Oscillating vortex generator jets have been used to Control Boundary layer separation from the suction side of a low-pressure turbine airfoil. A low Reynolds number (Re =25,000) case with low free-stream turbulence has been investigated with detailed measurements including profiles of mean and fluctuating velocity and turbulent shear stress. Ensemble averaged profiles are computed for times within the jet pulsing cycle, and integral parameters and local skin friction coefficients are computed from these profiles. The jets are injected into the mainflow at a compound angle through a spanwise row of holes in the suction surface. Preliminary tests showed that the jets were effective over a wide range of frequencies and amplitudes. Detailed tests were conducted with a maximum blowing ratio of 4. 7 and a dimensionless oscillation frequency of 0.65. The outward pulse from the jets in each oscillation cycle causes a disturbance to move down the airfoil surface. The leading and trailing edge celerities for the disturbance match those expected for a turbulent spot. The disturbance is followed by a calmed region. Following the calmed region, the Boundary layer does separate, but the separation bubble remains very thin. Results are compared to an unControlled baseline case in which the Boundary layer separated and did not reattach, and a case Controlled passively with a rectangular bar on the suction surface. The comparison indicates that losses will be substantially lower with the jets than in the baseline or passively Controlled cases.
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separation Control on low pressure turbine airfoils using synthetic vortex generator jets
ASME Turbo Expo 2003 collocated with the 2003 International Joint Power Generation Conference, 2003Co-Authors: Ralph J VolinoAbstract:Oscillating vortex generator jets have been used to Control Boundary layer separation from the suction side of a low-pressure turbine airfoil. A low Reynolds number (Re = 25,000) case with low free-stream turbulence has been investigated with detailed measurements including profiles of mean and fluctuating velocity and turbulent shear stress. Ensemble averaged profiles are computed for times within the jet pulsing cycle, and integral parameters and local skin friction coefficients are computed from these profiles. The jets are injected into the mainflow at a compound angle through a spanwise row of holes in the suction surface. Preliminary tests showed that the jets were effective over a wide range of frequencies and amplitudes. Detailed tests were conducted with a maximum blowing ratio of 4.7 and a dimensionless oscillation frequency of 0.65. The outward pulse from the jets in each oscillation cycle causes a disturbance to move down the airfoil surface. The leading and trailing edge celerities for the disturbance match those expected for a turbulent spot. The disturbance is followed by a calmed region. Following the calmed region, the Boundary layer does separate, but the separation bubble remains very thin. Results are compared to an unControlled baseline case in which the Boundary layer separated and did not reattach, and a case Controlled passively with a rectangular bar on the suction surface. The comparison indicates that losses will be substantially lower with the jets than in the baseline or passively Controlled cases.Copyright © 2003 by ASME
Rohit Gupta - One of the best experts on this subject based on the ideXlab platform.
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Closed-loop trailing-edge separation Control system using empirical mode decomposition
AIAA Journal, 2018Co-Authors: Rohit Gupta, Phillip J. AnsellAbstract:Active unsteady flow Control experiments were performed on a natural laminar flow airfoil at Rec=1.0×106. The goal of this study was to Control Boundary-layer separation across the trailing-edge re...
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closed loop trailing edge separation Control system using empirical mode decomposition
AIAA Journal, 2018Co-Authors: Rohit Gupta, Phillip J. AnsellAbstract:Active unsteady flow Control experiments were performed on a natural laminar flow airfoil at Rec=1.0×106. The goal of this study was to Control Boundary-layer separation across the trailing-edge region of the airfoil in off-design conditions. Active Control of separation was achieved using a series of blowing slots at the x/c=0.75 location. An adaptive closed-loop Controller was developed based on the empirical mode decomposition algorithm. This Controller was capable of automatically identifying the frequencies of natural instabilities in the flowfield, which were then used to set the driving frequencies of the flow Control system. The airfoil performance with closed-loop frequency Control was compared against a canonical open loop F+=1 actuation. The differences in flowfield characteristics between these two cases were investigated in detail using particle image velocimetry measurements across the trailing-edge region of the airfoil. Closed-loop frequency Control was observed to be associated with more ...
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open loop and closed loop trailing edge separation Control on a natural laminar flow airfoil
54th AIAA Aerospace Sciences Meeting 2016, 2016Co-Authors: Rohit Gupta, Phillip J. AnsellAbstract:Active Unsteady Flow Control experiments were performed on a Natural Laminar Flow, NLF 0414 airfoil at Rec = 1.0 × 10 6 . The goal of this study was to Control Boundary-layer separation across the trailing-edge region of the airfoil in off-design conditions. Both openloop and closed-loop Control approaches were used. Active Control of separation was achieved using a series of blowing slots at the x/c = 0.75 location. Open loop Control parameters were varied across a parametric range of jet amplitudes, actuation frequencies and duty cycles and performance measurements were acquired to identify the effectiveness of these actuation schemes. PIV measurements were acquired across a horizontal plane near the trailing edge region of the model to understand the effects of actuation on flow separation and the vortex dynamics associated with unsteady actuation. A closed loop Controller was developed to vary the actuation parameters in-situ using sensory feedback from the unsteady surface pressure measurements and adaptive modal decomposition methods. This closed-loop system was able to automatically Control the extent of separation such that a desired value of Cl was obtained.
John C Lin - One of the best experts on this subject based on the ideXlab platform.
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review of research on low profile vortex generators to Control Boundary layer separation
Progress in Aerospace Sciences, 2002Co-Authors: John C LinAbstract:Abstract An in-depth review of Boundary-layer flow-separation Control by a passive method using low-profile vortex generators is presented. The generators are defined as those with a device height between 10% and 50% of the Boundary-layer thickness. Key results are presented for several research efforts, all of which were performed within the past decade and a half where the majority of these works emphasize experimentation with some recent efforts on numerical simulations. Topics of discussion consist of both basic fluid dynamics and applied aerodynamics research. The fluid dynamics research includes comparative studies on separation Control effectiveness as well as device-induced vortex characterization and correlation. The comparative studies cover the Controlling of low-speed separated flows in adverse pressure gradient and supersonic shock-induced separation. The aerodynamics research includes several applications for aircraft performance enhancement and covers a wide range of speeds. Significant performance improvements are achieved through increased lift and/or reduced drag for various airfoils—low-Reynolds number, high-lift, and transonic—as well as highly swept wings. Performance enhancements for non-airfoil applications include aircraft interior noise reduction, inlet flow distortion alleviation inside compact ducts, and a more efficient overwing fairing. The low-profile vortex generators are best for being applied to applications where flow-separation locations are relatively fixed and the generators can be placed reasonably close upstream of the separation. Using the approach of minimal near-wall protuberances through substantially reduced device height, these devices can produce streamwise vortices just strong enough to overcome the separation without unnecessarily persisting within the Boundary layer once the flow-Control objective is achieved. Practical advantages of low-profile vortex generators, such as their inherent simplicity and low device drag, are demonstrated to be critically important for many applications as well.
Jeff Shubrooks - One of the best experts on this subject based on the ideXlab platform.
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Boundary Slope Control in Topology Optimization for Additive Manufacturing: For Self-Support and Surface Roughness
Journal of Manufacturing Science and Engineering, 2019Co-Authors: Cunfu Wang, Xiaoping Qian, William Dwight Gerstler, Jeff ShubrooksAbstract:This paper studies how to Control Boundary slope of optimized parts in density-based topology optimization for additive manufacturing (AM). Boundary slope of a part affects the amount of support structure required during its fabrication by additive processes. Boundary slope also has a direct relation with the resulting surface roughness from the AM processes, which in turn affects the heat transfer efficiency. By constraining the minimal Boundary slope, support structures can be eliminated or reduced for AM, and thus, material and postprocessing costs are reduced; by constraining the maximal Boundary slope, high-surface roughness can be attained, and thus, the heat transfer efficiency is increased. In this paper, the Boundary slope is Controlled through a constraint between the density gradient and the given build direction. This allows us to explicitly Control the Boundary slope through density gradient in the density-based topology optimization approach. We Control the Boundary slope through two single global constraints. An adaptive scheme is also proposed to select the thresholds of these two Boundary slope constraints. Numerical examples of linear elastic problem, heat conduction problem, and thermoelastic problems demonstrate the effectiveness and efficiency of the proposed formulation in Controlling Boundary slopes for additive manufacturing. Experimental results from metal 3D printed parts confirm that our Boundary slope-based formulation is effective for Controlling part self-support during printing and for affecting surface roughness of the printed parts.
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Boundary Slope Control in Topology Optimization for Additive Manufacturing
Volume 2: Materials; Joint MSEC-NAMRC-Manufacturing USA, 2018Co-Authors: Cunfu Wang, Xiaoping Qian, William Dwight Gerstler, Jeff ShubrooksAbstract:The paper studies how to Control Boundary slope of optimized parts in density-based topology optimization for additive manufacturing (AM). Boundary slope of a part affects the amount of support structure required during its fabrication by additive processes. Boundary slope also has direct relation with the resulting surface roughness from the AM processes, which in turn affects the heat transfer efficiency. By constraining the minimal Boundary slope, support structures can be eliminated or reduced for AM, and thus material and post-processing costs are reduced; by constraining the maximal Boundary slope, high surface roughness can be attained, and thus the heat transfer efficiency is increased. In this paper, the Boundary slope is Controlled through a constraint between the density gradient and the given build direction. This allows us to explicitly Control the Boundary slope through density gradient in the density-based topology optimization approach. We Control the Boundary slope through a single global constraint. Numerical examples on heat conduction problem, and coupled 2D and 3D thermoelastic problems demonstrate the effectiveness and efficiency of the proposed formulation in Controlling Boundary slopes for additive manufacturing.