The Experts below are selected from a list of 897 Experts worldwide ranked by ideXlab platform
Xin Zhang - One of the best experts on this subject based on the ideXlab platform.
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Aerodynamics of a heaving airfoil in ground effect
AIAA Journal, 2011Co-Authors: Juan Molina, Xin ZhangAbstract:The aerodynamic behavior of an inverted airfoil in ground effect under heaving motion was investigated numerically. A sinusoidal vertical movement perpendicular to a uniform freestream was imposed on the airfoil. The response showed a periodic pattern that repeated with the same frequency as the heaving motion. The effect of reduced frequency at several mean distances from the ground was examined. By analyzing the lag of the aerodynamic coefficients with respect to the vertical motion, the flow can be classified into different regimes. Three fundamental features that define these regimes have been identified: 1) ground effect, 2) incidence effect, and 3) added mass effect. At low frequencies, the airfoil can be assumed to be in a quasi-stationary motion and the ground effect governs the flow. The contribution of incidence effects becomes apparent at medium frequencies and can be explained by defining an effective angle of attack. The maximum Downforce is obtained at high effective angles of attack. As the frequency is increased even further, the only apparent effect is that of added mass. In this regime, Downforce is shown to be related to the vertical acceleration of the airfoil. These mechanisms are independent of Reynolds number.
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Detached eddy simulation of a double element wing in ground effect
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010Co-Authors: Jacques Heyder-bruckner, Xin ZhangAbstract:ow around an inverted double-element wing in ground eect was simulated using the detached-eddy simulation (DES) method, with the aim of investigating and capturing the complex ow. Various ride heights were investigated and the wing Downforce, surface pressure distribution and ow vorticity were validated against experimental data and compared to steady Reynolds-averaged Navier-Stokes (SRANS) simulations. DES predicts qualitatively accurate trends over the range of ride heights and it captures edge vortex breakdown which aects the force behavior and becomes increasingly unsteady as ride height is reduced. At low ride heights, ow reversal occurs in the wake beneath the ap’s center span but it does not cause a loss in ap Downforce.
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Flow separation control on a race car wing with vortex generators in ground effect
Journal of Fluids Engineering-transactions of The Asme, 2009Co-Authors: Yuichi Kuya, Xin Zhang, Kenji Takeda, Scott Beeton, Ted PandaleonAbstract:Flow separation control using vortex generators on an inverted wing in ground effect is experimentally investigated, and its performance is characterized in terms of forces and pressure distributions over a range of incidence and ride height. Counter-rotating and co-rotating rectangular-vane type vortex generators are tested on the suction surface of the wing. The effect of device height and spacing is investigated. The counter-rotating sub-boundary layer vortex generators and counter-rotating large-scale vortex generators on the wing deliver 23% and 10% improvements in the maximum Downforce, respectively, compared with the clean wing, at an incidence of one degree, and delay the onset of the Downforce reduction phenomenon. The counter-rotating sub-boundary layer vortex generators exhibit up to 26% improvement in Downforce and 10% improvement in aerodynamic efficiency at low ride heights. Chordwise pressure measurement confirms that both counter-rotating vortex generator configurations suppress flow separation, while the co-rotating vortex generators exhibit negligible effectiveness. This work shows that a use of vortex generators, notably of the counter-rotating sub-boundary layer vortex generator type, can be effective at controlling flow separation, with a resultant improvement in Downforce for relatively low drag penalty
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Ground Effect Aerodynamics of Race Cars
Applied Mechanics Reviews, 2006Co-Authors: Xin Zhang, Willem Toet, Jonathan ZerihanAbstract:We review the progress made during the last thirty years on ground effect aerodynamics associated with race cars, in particular open wheel race cars. Ground effect aerodynamics of race cars is concerned with generating Downforce, principally via low pressure on the surfaces nearest to the ground. The “ground effected” parts of an open wheeled car's aerodynamics are the most aerodynamically efficient and contribute less drag than that associated with, for example, an upper rear wing. Whilst drag reduction is an important part of the research, Downforce generation plays a greater role in lap time reduction. Aerodynamics plays a vital role in determining speed and acceleration (including longitudinal acceleration but principally cornering acceleration), thus performance. Attention is paid to wings and diffusers in ground effect and wheel aerodynamics. For the wings and diffusers in ground effect, major physical features are identified and force regimes classified, including the phenomena of Downforce enhancement, maximum Downforce and Downforce reduction. In particular the role played by force enhancement edge vortices is demonstrated. Apart from model tests, advances and problems in numerical modeling of ground effect aerodynamics are also reviewed and discussed.
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Edge vortices of a double element wing in ground effect
Journal of Aircraft, 2004Co-Authors: Xin Zhang, Jonathan ZerihanAbstract:The influence of edge vortices generated by a generic double-element wing on force behaviors are discussed. The wing is equipped with end plates and operates in ground effect. The Downforce-vs-height curve is divided into three distinct regions according to ground proximity and flap setting. As the wing is moved from a height in freestream to the ground plane, the Downforce first experiences a rapid enhancement (region A). This process is accompanied by the presence of a concentrated vortex off the edge of the side plate and diffuser effect of the wing. At a critical height, the vortex breaks down and its contribution to the Downforce is lost. This creates a change in the gradient of the Downforce slope. The force enhancement process continues as the height of the wing is reduced (region B); the main diffuser effect is still present. The Downforce is lost below a height where the maximum Downforce is reached, due to large separation on the wing (region C). The importance of the edge vortices in defining the characteristics of the Downforce curve is established.
Mansour Moinpour - One of the best experts on this subject based on the ideXlab platform.
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In Situ Investigation of Slurry Flow Fields during CMP
Journal of The Electrochemical Society, 2009Co-Authors: N. Mueller, Chris Rogers, Vincent P. Manno, Robert D. White, Mansour MoinpourAbstract:The objective of this work is to obtain in situ slurry fluid flow data during the chemical mechanical planarization (CMP) process. Slurry flow affects the material removal processes, the creation of defects, and consumable use during CMP, and therefore impacts the cost and quality of polishing. Wafer-scale flow visualization using seeded slurry was accomplished for a variable applied load (0.3-2.5 psi Downforce), wafer rotation speed (0 and 33 rpm), slurry injection locations, and various pad types (flat, XY grooved, and AC grooved). In situ pad conditioning was employed in all experiments. The data indicated complex slurry flow fields on the pad surface in the wafer vicinity, which are influenced by slurry injection point, pad grooving, Downforce, and wafer/conditioner rotation. Injection location and pad type were shown to have the strongest impact on the variation in the fluid flow fields obtained.
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Measurements of Slurry Film Thickness and Wafer Drag during CMP
Journal of The Electrochemical Society, 2004Co-Authors: Joseph Lu, Ara Philipossian, Chris Rogers, Vincent P. Manno, Sriram Anjur, Mansour MoinpourAbstract:dIntel Corporation, Santa Clara, California 95052-8119, USA Chemical mechanical planarization ~CMP! is a process widely used for the manufacture of silicon integrated circuits. In this work, we measured the thickness of the slurry film between the wafer and the pad during polish while simultaneously measuring the frictional drag. All experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer Downforce control. Dual emission laser-induced fluorescence techniques optically measured the slurry film thickness through a dual-camera imaging system. The resulting data are discussed for wafers polished with a 3.1 wt % abrasive concentration slurry solution on Freudenberg’s FX-9 polishing pads. It was found that the degree of surface curvature of the wafer substrate significantly influences the slurry film thickness and wafer drag, and therefore, the polish. The convex wafer shows the expected behavior of increased Downforce reduces the slurry film thickness and increases the coefficient of friction. Further, as the pad speeds up, the slurry thickness increases and the friction decreases. The concave wafer shows no change in slurry film thickness and a decrease in the frictional coefficient with increasing Downforce. Both the film thickness and frictional coefficient appear to decrease slightly with increasing pad speed. This difference between the two wafer shapes reflects the different fluid mechanics in each case.
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The Effect of Wafer Shape on Slurry Film Thickness and Friction Coefficients in Chemical Mechanical Planarization
MRS Proceedings, 2000Co-Authors: Joseph Lu, Ara Philipossian, J. Coppeta, Chris Rogers, Vincent P. Manno, Livia Racz, Mansour Moinpour, Frank KaufmancAbstract:ABSTRACTThe fluid film thickness and drag during chemical-mechanical polishing are largely dependent on the shape of the wafer polished. In this study we use dual emission laser induced fluorescence to measure the film thickness and a strain gage, mounted on the polishing table, to measure the friction force between the wafer and the pad. All measurements are taken during real polishing processes. The trends indicate that with a convex wafer in contact with the polishing pad, the slurry layer increases with increasing platen speed and decreases with increasing Downforce. The drag force decreases with increasing platen speed and increases with increasing Downforce. These similarities are observed for both in-situ and ex-situ conditioning. However, these trends are significantly different for the case of a concave wafer in contact with the polishing pad. During ex-situ conditioning the trends are similar as with a convex wafer. However, in-situ conditioning decreases the slurry film layer with increasing platen speed, and increases it with increasing Downforce in the case of the concave wafer. The drag force increases with increasing platen speed as well as increasing Downforce. Since we are continually polishing, the wafer shape does change over the course of each experiment causing a larger error in repeatability than the measurement error itself. Different wafers are used throughout the experiment and the results are consistent with the variance of the wafer shape. Local pressure measurements on the rotating wafer help explain the variances in fluid film thickness and friction during polishing.
Kazuhiro Nakata - One of the best experts on this subject based on the ideXlab platform.
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three defect types in friction stir welding of aluminum die casting alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Young Gon Kim, Hidetoshi Fujii, Takuya Tsumura, T Komazaki, Kazuhiro NakataAbstract:For different tool plunge Downforces, the optimum FSW conditions of aluminum die casting alloy were examined. The higher the tool plunge Downforce is, the wider the range of the optimum FSW conditions is. The following three different types of defects are formed, depending on the FSW conditions. (1) A large mass of flash due to the excess heat input; (2) cavity or groove-like defects caused by insufficient heat input; and (3) cavity caused by the abnormal stirring. As for the abnormal stirring, it is clearly seen that the shape of the top part on the advancing side in the stir zone is completely different. For this type of defect, the effect of the tool plunge Downforce is small, though the size of the defect due to insufficient heat input significantly decreases with the increasing Downforce.
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effect of tool plunging Downforce on friction stir welding of adc12 die cast alloy
Transactions of J W R I, 2003Co-Authors: Kazuhiro Nakata, T Komazaki, Taichi Murakami, Masao Ushio, 中田 一博, 村上 太一, 駒崎 徹, 牛尾 誠夫Abstract:Friction Stir Welding (FSW) has been attracting attention as a useful joining process for casts with superior characteristics to conventional fusion welding. It is well known that arc welding of aluminum die cast alloy isvery difficult because of the formation of blowholes and cracks. In this research, the effect of the tool plunge Downforce on FSW joints of SDC12 was evaluated for establishing the range of the optimum welding conditions in FSW. The range of the optimum FSW conditions for sound joints expanded with increasing tool plunge Downforce, because the area of contact of the tool shoulder with the workpiece increased and plastic metal flow was activated.
Jonathan Zerihan - One of the best experts on this subject based on the ideXlab platform.
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Ground Effect Aerodynamics of Race Cars
Applied Mechanics Reviews, 2006Co-Authors: Xin Zhang, Willem Toet, Jonathan ZerihanAbstract:We review the progress made during the last thirty years on ground effect aerodynamics associated with race cars, in particular open wheel race cars. Ground effect aerodynamics of race cars is concerned with generating Downforce, principally via low pressure on the surfaces nearest to the ground. The “ground effected” parts of an open wheeled car's aerodynamics are the most aerodynamically efficient and contribute less drag than that associated with, for example, an upper rear wing. Whilst drag reduction is an important part of the research, Downforce generation plays a greater role in lap time reduction. Aerodynamics plays a vital role in determining speed and acceleration (including longitudinal acceleration but principally cornering acceleration), thus performance. Attention is paid to wings and diffusers in ground effect and wheel aerodynamics. For the wings and diffusers in ground effect, major physical features are identified and force regimes classified, including the phenomena of Downforce enhancement, maximum Downforce and Downforce reduction. In particular the role played by force enhancement edge vortices is demonstrated. Apart from model tests, advances and problems in numerical modeling of ground effect aerodynamics are also reviewed and discussed.
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Edge vortices of a double element wing in ground effect
Journal of Aircraft, 2004Co-Authors: Xin Zhang, Jonathan ZerihanAbstract:The influence of edge vortices generated by a generic double-element wing on force behaviors are discussed. The wing is equipped with end plates and operates in ground effect. The Downforce-vs-height curve is divided into three distinct regions according to ground proximity and flap setting. As the wing is moved from a height in freestream to the ground plane, the Downforce first experiences a rapid enhancement (region A). This process is accompanied by the presence of a concentrated vortex off the edge of the side plate and diffuser effect of the wing. At a critical height, the vortex breaks down and its contribution to the Downforce is lost. This creates a change in the gradient of the Downforce slope. The force enhancement process continues as the height of the wing is reduced (region B); the main diffuser effect is still present. The Downforce is lost below a height where the maximum Downforce is reached, due to large separation on the wing (region C). The importance of the edge vortices in defining the characteristics of the Downforce curve is established.
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Off-surface aerodynamic measurements of a wing in ground effect
Journal of Aircraft, 2003Co-Authors: Xin Zhang, Jonathan ZerihanAbstract:The off-surface aerodynamic characteristics of a wing in ground effect are investigated using a number of methods including laser Doppler anemometry and particle image velocimetry. The study focuses on two aspects of the flow: turbulentwake andedge vortex. These features are closely associated with the behaviorof theaerodynamic force in ground effect. The size of the wake increases in proximity to the ground. A downward shift of the path of the wake is also observed. Discrete vortex shedding is seen to occur behind the wing. As the wing height is reduced, separation occurred on the suction surface of the wing, and the spanwise vortex shedding is found to couple with a flapping motion of the wake in the transverse direction. An edge vortex is also observed off the edge of the end plate of the wing, which contributes to force enhancement and helps to define the force behavior in the force enhancement region. The rate of change in the Downforce vs height curve is linked to the strength of the edge vortex. The vortex breakdown signals a slowdown in the force enhancement. When the maximum Downforce height is reached, the edge vortex breaks down completely.
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Aerodynamics of a Double-Element Wing in Ground Effect
AIAA Journal, 2003Co-Authors: Xin Zhang, Jonathan ZerihanAbstract:A study was performed of a cambered, double-element, high-lift wing operating in ground effect. The effect of ground proximity and flap setting has been quantified in terms of aerodynamic performance and off-surface flowfield characteristics. Measurements include surface pressure taps, force, surface streaklines, and laser doppier anemometry (LDA). It was found from the Haw visualization that the flow is three-dimensional (3D) towards the wing tip with the main element generating most of the Downforce, but retains quasi-2D features near the centre of the wing. However, at large heights the Downforce increases asymptotically with a reduction in height, Then there is either a plateau, in the case of a low flap angle, or a reduction in down-force, in the case of a large flap angle. The Downforce then increases again until it reaches a maximum, and then reduces at a height near the ground. The maximum Downforce is dictated by gains in Downforce from lower surface suction increases and losses in Downforce due to upper surface pressure losses and lower surface suction losses, with a reduction in height. For the high flap angle, there is a sharp reduction just beyond the maximum, due to the boundary layer separating, and a resultant loss of circulation on. the main element.
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Aerodynamics of a single element wing in ground effect
Journal of Aircraft, 2000Co-Authors: Jonathan Zerihan, Xin ZhangAbstract:An investigation was conducted on the performance characteristics and flowfield phenomena of a wing in ground effect. Model tests were performed in low-speed wind tunnels equipped with moving ground. A highly cambered single element wing, with the suction surface nearest to the ground, was used to investigate the effect of changing both the ride height from the ground and the incidence. Data obtained in model tests included force balance measurements, surface pressure results, and surface oil flow visualization. Results are compared with the freestream case. As the ride height is reduced, higher levels of Downforce were recorded; at clearances between the suction surface and the ground of less than 20% chord, the Downforce is significantly higher. Closer to the ground, at a ride height of less than 10% chord, Downforce drops as the wing stalls. This force reduction phenomenon is shown to be due to trailing-edge separation of the boundary layer
Ara Philipossian - One of the best experts on this subject based on the ideXlab platform.
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effect of conditioner type and Downforce and pad surface micro texture on sio2 chemical mechanical planarization performance
Micromachines, 2019Co-Authors: Jeffrey Mcallister, Calliandra Stuffle, Yasa Sampurno, Dale L Hetherington, Jon Sierra Suarez, Leonard Borucki, Ara PhilipossianAbstract:Based on a previous work where we investigated the effect of conditioner type and Downforce on the evolution of pad surface micro-texture during break-in, we have chosen certain break-in conditions to carry out subsequent blanket SiO2 wafer polishing studies. Two different conditioner discs were used in conjunction with up to two different conditioning Downforces. For each disc-Downforce combination, mini-marathons were run using SiO2 wafers. Prior to polishing, each pad was broken-in for 30 min with one of the conditioner-Downforce combinations. The goal of this study was to polish wafers after this break-in to see how the polishing process behaved immediately after break-in. One of the discs used in this study produced similar micro-texture results at both Downforces, which echoed the results seen in the mini-marathon. When comparing the different polishing results obtained from breaking-in the pad with the different discs used in this study, the coefficient of friction (COF) and SiO2 removal rate (RR) were uncorrelated in all cases. However, the use of different discs resulted in different COF and RR trends. The uncorrelated COF and RR, as well as the differing trends, were explained by pad micro-texture results (i.e. the differing amount of fractured, poorly supported pad asperity summits).
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Measurements of Slurry Film Thickness and Wafer Drag during CMP
Journal of The Electrochemical Society, 2004Co-Authors: Joseph Lu, Ara Philipossian, Chris Rogers, Vincent P. Manno, Sriram Anjur, Mansour MoinpourAbstract:dIntel Corporation, Santa Clara, California 95052-8119, USA Chemical mechanical planarization ~CMP! is a process widely used for the manufacture of silicon integrated circuits. In this work, we measured the thickness of the slurry film between the wafer and the pad during polish while simultaneously measuring the frictional drag. All experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer Downforce control. Dual emission laser-induced fluorescence techniques optically measured the slurry film thickness through a dual-camera imaging system. The resulting data are discussed for wafers polished with a 3.1 wt % abrasive concentration slurry solution on Freudenberg’s FX-9 polishing pads. It was found that the degree of surface curvature of the wafer substrate significantly influences the slurry film thickness and wafer drag, and therefore, the polish. The convex wafer shows the expected behavior of increased Downforce reduces the slurry film thickness and increases the coefficient of friction. Further, as the pad speeds up, the slurry thickness increases and the friction decreases. The concave wafer shows no change in slurry film thickness and a decrease in the frictional coefficient with increasing Downforce. Both the film thickness and frictional coefficient appear to decrease slightly with increasing pad speed. This difference between the two wafer shapes reflects the different fluid mechanics in each case.
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The Effect of Wafer Shape on Slurry Film Thickness and Friction Coefficients in Chemical Mechanical Planarization
MRS Proceedings, 2000Co-Authors: Joseph Lu, Ara Philipossian, J. Coppeta, Chris Rogers, Vincent P. Manno, Livia Racz, Mansour Moinpour, Frank KaufmancAbstract:ABSTRACTThe fluid film thickness and drag during chemical-mechanical polishing are largely dependent on the shape of the wafer polished. In this study we use dual emission laser induced fluorescence to measure the film thickness and a strain gage, mounted on the polishing table, to measure the friction force between the wafer and the pad. All measurements are taken during real polishing processes. The trends indicate that with a convex wafer in contact with the polishing pad, the slurry layer increases with increasing platen speed and decreases with increasing Downforce. The drag force decreases with increasing platen speed and increases with increasing Downforce. These similarities are observed for both in-situ and ex-situ conditioning. However, these trends are significantly different for the case of a concave wafer in contact with the polishing pad. During ex-situ conditioning the trends are similar as with a convex wafer. However, in-situ conditioning decreases the slurry film layer with increasing platen speed, and increases it with increasing Downforce in the case of the concave wafer. The drag force increases with increasing platen speed as well as increasing Downforce. Since we are continually polishing, the wafer shape does change over the course of each experiment causing a larger error in repeatability than the measurement error itself. Different wafers are used throughout the experiment and the results are consistent with the variance of the wafer shape. Local pressure measurements on the rotating wafer help explain the variances in fluid film thickness and friction during polishing.