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Kunihiko Taira  One of the best experts on this subject based on the ideXlab platform.

laminar vortex dynamics around forward Swept Wings
arXiv: Fluid Dynamics, 2021CoAuthors: Kai Zhang, Kunihiko TairaAbstract:ForwardSwept Wings offer unique advantages in the aerodynamic performance of air vehicles. However, the lowReynoldsnumber characteristics of such Wings have not been explored in the past. In this work, we numerically study laminar separated flows over forwardSwept Wings with semi aspect ratios $sAR=0.5$ to 2 at a chordbased Reynolds number of 400. ForwardSwept Wings generate wakes that are significantly different from those of backwardSwept Wings. For lowaspectratio forward Wings, the wakes remain steady due to the strong downwash effects induced by the tip vortices. For larger aspect ratio, the downwash effects weaken over the inboard regions of the wing, allowing unsteady vortex shedding to occur. Further larger aspect ratio allows for the formation of streamwise vortices for highlySwept Wings, stabilizing the flow. ForwardSwept Wings can generate enhanced lift at high angles of attack than the unSwept and backwardSwept Wings, with the cost of high drag. We show through force element analysis that the increased lift of forwardSwept Wings is attributed to the vortical structure that is maintained by the tipvortexinduced downwash over the outboard region of wing span. The current findings offer a detailed understanding of the sweep effects on laminar separated flows over forwardSwept Wings, and invite innovative designs of highlift devices.

laminar separated flows over finite aspect ratio Swept Wings
Journal of Fluid Mechanics, 2020CoAuthors: Kai Zhang, Shelby Hayostek, Michael Amitay, Anton Burtsev, Vassilios Theofilis, Kunihiko TairaAbstract:We perform direct numerical simulations of laminar separated flows over finiteaspectratio Swept Wings at a chordbased Reynolds number of Wings due to weakened downwash induced by the tip vortices. With increasing sweep angle, the source of threedimensionality transitions from the tip to the midspan. The threedimensional midspan effects are responsible for the formation of the stationary vortical structures at the inboard part of the span, which expands the steady wake region to higher aspect ratios. At higher aspect ratios, the midspan effects of Swept Wings diminish at the outboard region, allowing unsteady vortex shedding to develop near the tip. In the wakes of highly Swept Wings, streamwise fingerlike structures form repetitively along the wing span, providing a stabilizing effect. The insights revealed from this study can aid the design of highlift devices and serve as a stepping stone for understanding the complex wake dynamics at higher Reynolds numbers and those generated by unsteady wing manoeuvres.

Aerodynamic characterization of lowaspectratio Swept Wings at $Re=400$
arXiv: Fluid Dynamics, 2020CoAuthors: Kai Zhang, Kunihiko TairaAbstract:We perform unsteady threedimensional direct numerical simulations to study the aerodynamic characteristics of finiteaspectratio Swept Wings with a NACA 0015 crosssection at a chordbased Reynolds number of 400. The effects of the sweep angle ($\Lambda=0^{\circ}45^{\circ}$) on the aerodynamic force coefficients are examined for finiteaspectratio Wings ($sAR=0.5$, 1, and 2) over a wide range of angles of attack ($\alpha=0^{\circ}30^{\circ}$). The unsteady laminar separated flows exhibit complex aerodynamic characteristics with respect to these parameters. The introduction of sweep enhances lift for Wings with low aspect ratios of $sAR=0.5$ and 1, due to the lift generated by the vortical structures near the midspan. For these cases, the dependence of drag coefficients on the sweep angle is less noticeable, particularly at lower angles of attack. The lifttodrag ratios for lowaspectratio Wings increase with the sweep angle. However, such favorable effects of sweep angle on the lift coefficients and lifttodrag ratios are not observed for Wings with higher aspect ratios, where the midspan effects are relatively weaker over the wing span. The results herein provide a laminar aerodynamic characterization of the lowaspectratio Wings and complement the unsteady lowReynoldsnumber aerodynamic database with highlight on the effect of sweep.

aerodynamic characterization of low aspect ratio Swept Wings at re 400
arXiv: Fluid Dynamics, 2020CoAuthors: Kai Zhang, Kunihiko TairaAbstract:We perform unsteady threedimensional direct numerical simulations to study the aerodynamic characteristics of finiteaspectratio Swept Wings with a NACA 0015 crosssection at a chordbased Reynolds number of 400. The effects of the sweep angle ($\Lambda=0^{\circ}45^{\circ}$) on the aerodynamic force coefficients are examined for finiteaspectratio Wings ($sAR=0.5$, 1, and 2) over a wide range of angles of attack ($\alpha=0^{\circ}30^{\circ}$). The unsteady laminar separated flows exhibit complex aerodynamic characteristics with respect to these parameters. The introduction of sweep enhances lift for Wings with low aspect ratios of $sAR=0.5$ and 1, due to the lift generated by the vortical structures near the midspan. For these cases, the dependence of drag coefficients on the sweep angle is less noticeable, particularly at lower angles of attack. The lifttodrag ratios for lowaspectratio Wings increase with the sweep angle. However, such favorable effects of sweep angle on the lift coefficients and lifttodrag ratios are not observed for Wings with higher aspect ratios, where the midspan effects are relatively weaker over the wing span. The results herein provide a laminar aerodynamic characterization of the lowaspectratio Wings and complement the unsteady lowReynoldsnumber aerodynamic database with highlight on the effect of sweep.
Kai Zhang  One of the best experts on this subject based on the ideXlab platform.

laminar vortex dynamics around forward Swept Wings
arXiv: Fluid Dynamics, 2021CoAuthors: Kai Zhang, Kunihiko TairaAbstract:ForwardSwept Wings offer unique advantages in the aerodynamic performance of air vehicles. However, the lowReynoldsnumber characteristics of such Wings have not been explored in the past. In this work, we numerically study laminar separated flows over forwardSwept Wings with semi aspect ratios $sAR=0.5$ to 2 at a chordbased Reynolds number of 400. ForwardSwept Wings generate wakes that are significantly different from those of backwardSwept Wings. For lowaspectratio forward Wings, the wakes remain steady due to the strong downwash effects induced by the tip vortices. For larger aspect ratio, the downwash effects weaken over the inboard regions of the wing, allowing unsteady vortex shedding to occur. Further larger aspect ratio allows for the formation of streamwise vortices for highlySwept Wings, stabilizing the flow. ForwardSwept Wings can generate enhanced lift at high angles of attack than the unSwept and backwardSwept Wings, with the cost of high drag. We show through force element analysis that the increased lift of forwardSwept Wings is attributed to the vortical structure that is maintained by the tipvortexinduced downwash over the outboard region of wing span. The current findings offer a detailed understanding of the sweep effects on laminar separated flows over forwardSwept Wings, and invite innovative designs of highlift devices.

laminar separated flows over finite aspect ratio Swept Wings
Journal of Fluid Mechanics, 2020CoAuthors: Kai Zhang, Shelby Hayostek, Michael Amitay, Anton Burtsev, Vassilios Theofilis, Kunihiko TairaAbstract:We perform direct numerical simulations of laminar separated flows over finiteaspectratio Swept Wings at a chordbased Reynolds number of Wings due to weakened downwash induced by the tip vortices. With increasing sweep angle, the source of threedimensionality transitions from the tip to the midspan. The threedimensional midspan effects are responsible for the formation of the stationary vortical structures at the inboard part of the span, which expands the steady wake region to higher aspect ratios. At higher aspect ratios, the midspan effects of Swept Wings diminish at the outboard region, allowing unsteady vortex shedding to develop near the tip. In the wakes of highly Swept Wings, streamwise fingerlike structures form repetitively along the wing span, providing a stabilizing effect. The insights revealed from this study can aid the design of highlift devices and serve as a stepping stone for understanding the complex wake dynamics at higher Reynolds numbers and those generated by unsteady wing manoeuvres.

Aerodynamic characterization of lowaspectratio Swept Wings at $Re=400$
arXiv: Fluid Dynamics, 2020CoAuthors: Kai Zhang, Kunihiko TairaAbstract:We perform unsteady threedimensional direct numerical simulations to study the aerodynamic characteristics of finiteaspectratio Swept Wings with a NACA 0015 crosssection at a chordbased Reynolds number of 400. The effects of the sweep angle ($\Lambda=0^{\circ}45^{\circ}$) on the aerodynamic force coefficients are examined for finiteaspectratio Wings ($sAR=0.5$, 1, and 2) over a wide range of angles of attack ($\alpha=0^{\circ}30^{\circ}$). The unsteady laminar separated flows exhibit complex aerodynamic characteristics with respect to these parameters. The introduction of sweep enhances lift for Wings with low aspect ratios of $sAR=0.5$ and 1, due to the lift generated by the vortical structures near the midspan. For these cases, the dependence of drag coefficients on the sweep angle is less noticeable, particularly at lower angles of attack. The lifttodrag ratios for lowaspectratio Wings increase with the sweep angle. However, such favorable effects of sweep angle on the lift coefficients and lifttodrag ratios are not observed for Wings with higher aspect ratios, where the midspan effects are relatively weaker over the wing span. The results herein provide a laminar aerodynamic characterization of the lowaspectratio Wings and complement the unsteady lowReynoldsnumber aerodynamic database with highlight on the effect of sweep.

aerodynamic characterization of low aspect ratio Swept Wings at re 400
arXiv: Fluid Dynamics, 2020CoAuthors: Kai Zhang, Kunihiko TairaAbstract:We perform unsteady threedimensional direct numerical simulations to study the aerodynamic characteristics of finiteaspectratio Swept Wings with a NACA 0015 crosssection at a chordbased Reynolds number of 400. The effects of the sweep angle ($\Lambda=0^{\circ}45^{\circ}$) on the aerodynamic force coefficients are examined for finiteaspectratio Wings ($sAR=0.5$, 1, and 2) over a wide range of angles of attack ($\alpha=0^{\circ}30^{\circ}$). The unsteady laminar separated flows exhibit complex aerodynamic characteristics with respect to these parameters. The introduction of sweep enhances lift for Wings with low aspect ratios of $sAR=0.5$ and 1, due to the lift generated by the vortical structures near the midspan. For these cases, the dependence of drag coefficients on the sweep angle is less noticeable, particularly at lower angles of attack. The lifttodrag ratios for lowaspectratio Wings increase with the sweep angle. However, such favorable effects of sweep angle on the lift coefficients and lifttodrag ratios are not observed for Wings with higher aspect ratios, where the midspan effects are relatively weaker over the wing span. The results herein provide a laminar aerodynamic characterization of the lowaspectratio Wings and complement the unsteady lowReynoldsnumber aerodynamic database with highlight on the effect of sweep.
Ohseop Song  One of the best experts on this subject based on the ideXlab platform.

Aileron Reversal of Nonuniform and Swept Composite Aircraft Wings
Journal of Aircraft, 2013CoAuthors: Keuntaek Kim, Ohseop SongAbstract:In this paper, an analytical study on the aileron reversal characteristics of the anisotropic composite Swept Wings of aircraft via the extended Galerkin method is presented, and the Wings are modeled as nonuniform, thinwalled beams with bending–twist structural couplings induced by a circumferentially asymmetric stiffness configuration. For this study, nonclassical parameters such as warping restraint, transverse shear flexibility, and bending–twist structural coupling are incorporated. Further, design parameters of Wings such as taper and aspect ratios, sweep angle, initial angle of attack, aileron deflection, and ratios of spanwise and chordwise lengths of the aileron to the wing are newly investigated. The results of this study could play an important role in more efficient designs of composite thinwalled Swept Wings.

On the static aeroelastic tailoring of composite aircraft Swept Wings modelled as thinwalled beam structures
Composites Engineering, 1992CoAuthors: Liviu Librescu, Ohseop SongAbstract:The subcritical static aeroelastic response and the divergence instability of Sweptforward aircraft wing structures constructed of anisotropic composite materials is analyzed. The new element distinguishing this study from the previous, existing ones is the structural model in which framework this problem is treated. In this sense, in contrast to the classical platebeam or solidbeam models traditionally used in the study of these problems, the thinwalled anisotropic composite beam model is adopted here. The model used incorporates a number of nonclassical effects. Among these are the anisotropy of the material of the constituent layers, the transverse shear deformation and the primary and secondary warping effects. Within the framework of this study, in addition to an assessment of the influence of the previously mentioned effects, the aeroelastic tailoring technique is applied and as a result, a series of conclusions concerning the enhancement of the static aeroelastic response characteristics of aeronautical wing structures made of advanced composite materials are outlined. © 1992.
Mario Vargas  One of the best experts on this subject based on the ideXlab platform.

time sequence observations of the formation of ice accretions on Swept Wings
46th AIAA Aerospace Sciences Meeting and Exhibit, 2008CoAuthors: Mario Vargas, Jenching TsaoAbstract:This work presents the results of two complementary experiments, one conducted in the Icing Research Tunnel (IRT) at NASA Glenn Research Center and the other in the Goodrich Icing Wind Tunnel (IWT). The experiments were designed to study in real time the process by which ice accretions are formed on Swept Wings. In the IRT experiment a time sequence imaging technique (TSIT) was used to obtain real time data during the ice accretion formation. The time sequence photographic data was used to study the process frame by frame and to create movies of how the process developed in real time. A nonactivated heater located on the leading edge was used to study its effect on the formation of the ice shape. In the IWT experiment an improved TSIT was tested and additional data was taken at a baseline condition to clarify and complement the data from the IRT. The smaller IWT allowed greater optical access than the IRT providing increased field of view and an alternate grazing angle view. The data from the two experiments led to a more detailed conceptual model of how ice accretions develop.

current experimental basis for modeling ice accretions on Swept Wings
4th AIAA Theoretical Fluid Mechanics Meeting, 2005CoAuthors: Mario VargasAbstract:This work presents a review of the experimental basis for modeling ice accretions on Swept Wings. Experimental work related to ice accretion physics on Swept Wings conducted between 1954 and 2004 is reviewed. Proposed models or explanations of scallop formations are singled out and discussed. Special emphasis is placed on reviewing the work done to determine the basic macroscopic mechanisms of scallop formation. The role of feather growth and its connection to scallop growth is discussed. Conceptual steps in modeling scallop formations are presented. Research elements needed for modeling are discussed.

ice accretion formations on a naca 0012 Swept wing tip in natural icing conditions
40th AIAA Aerospace Sciences Meeting & Exhibit, 2002CoAuthors: Mario Vargas, Julius Giriunas, Thomas P RatvaskyAbstract:An experiment was conducted in the DeHavilland DHC6 Twin Otter Icing Research Aircraft at NASA Glenn Research Center to study the formation of ice accretions on Swept Wings in natural icing conditions. The experiment was designed to obtain ice accretion data to help determine if the mechanisms of ice accretion formation observed in the Icing Research Tunnel are present in natural icing conditions. The experiment in the Twin Otter was conducted using a NACA 0012 Swept wing tip. The model enabled data acquisition at 0 deg, 15 deg, 25 deg, 30 deg, and 45 deg sweep angles. Casting data, ice shape tracings, and closeup photographic data were obtained. The results showed that the mechanisms of ice accretion formation observed inflight agree well with the ones observed in the Icing Research Tunnel. Observations on the end cap of the airfoil showed the same strong effect of the local sweep angle on the formation of scallops as observed in the tunnel.

LWC and Temperature Effects on Ice Accretion Formation on Swept Wings at Glaze Ice Conditions
38th Aerospace Sciences Meeting and Exhibit, 2000CoAuthors: Mario Vargas, Eli ReshotkoAbstract:An experiment was conducted to study the effect of liquid water content and temperature on the critical distance in ice accretion formation on Swept Wings at glaze ice conditions. The critical distance is defined as the distance from the attachment line to tile beginning of the zone where roughness elements develop into glaze ice feathers. A baseline case of 150 mph, 25 F, 0.75 g/cu m. Cloud Liquid Water Content (LWC) and 20 micrometers in Water Droplet Median Volume Diameter (MVD) was chosen. Icing runs were performed on a NACA 0012 Swept wing tip at 150 mph and MVD of 20 micrometers for liquid water contents of 0.5 g/cu m, 0.75 g/cu m, and 1.0 g/cu m, and for total temperatures of 20 F, 25 F and 30 F. At each tunnel condition, the sweep angle was changed from 0 deg to 45 deg in 5 deg increments. Casting data, ice shape tracings, and closeup photographic data were obtained. The results showed that decreasing the LWC to 0.5 g/cu m decreases the value of the critical distance at a given sweep angle compared to the baseline case, and starts the formation of complete scallops at 30 sweep angle. Increasing the LWC to 1.0 g/cu m increases the value of the critical distance compared to the baseline case, the critical distance remains always above 0 millimeters and complete scallops are not formed. Decreasing the total temperature to 20 F decreases the critical distance with respect to the baseline case and formation of complete scallops begins at 25 deg sweep angle. When the total temperature is increased to 30 F, bumps covered with roughness elements appear on the ice accretion at 25 deg and 30 deg sweep angles, large ice structures appear at 35 deg and 40 deg sweep angles, and complete scallops are formed at 45 deg sweep angle.

Parametric Experimental Study of the Formation of Glaze Ice Shapes on Swept Wings
37th Aerospace Sciences Meeting and Exhibit, 1999CoAuthors: Mario Vargas, Eli ReshotkoAbstract:An experiment was conducted to study the effect of velocity and sweep angle on the critical distance in ice accretion formation on Swept Wings at glaze ice conditions. The critical distance is defined as the distance from the attachment line to the beginning of the zone where roughness elements develop into glaze ice feathers. Icing runs were performed on a NACA 00 1 2 Swept wing tip at velocities of 75, 100, 150, and 200 miles per hour. At each velocity and tunnel condition, the sweep angle was changed from 0 deg to 45 deg at 5 deg increments. Casting data, ice shape tracings, and closeup photographic data were obtained. The results showed that at given velocity and tunnel conditions, as the sweep angle is increased from 0 deg to 25 deg the critical distance slowly decreases. As the sweep angle is increased past 25 deg, the critical distance starts decreasing more rapidly. For 75 and 100 mph it reaches a value of 0 millimeters at 35 deg. For 150 and 200 mph it reaches a value of 0 millimeters at 40 deg. On the ice accretion, as the sweep angle is increased from 0 deg to 25 deg, the extent of the attachment line zone slowly decreases. In the glaze ice feathers zone, the angle that the preferred direction of growth of the feathers makes with respect to the attachment line direction increases. But overall, the ice accretions remain similar to the 0 deg sweep angle case. As the sweep angle is increased above 25 deg, the extent of the attachment line zone decreases rapidly and complete scallops form at 35 deg sweep angle for 75 and 100 mph, and at 40 deg for 150 and 200 mph.
Vassilios Theofilis  One of the best experts on this subject based on the ideXlab platform.

laminar separated flows over finite aspect ratio Swept Wings
Journal of Fluid Mechanics, 2020CoAuthors: Kai Zhang, Shelby Hayostek, Michael Amitay, Anton Burtsev, Vassilios Theofilis, Kunihiko TairaAbstract:We perform direct numerical simulations of laminar separated flows over finiteaspectratio Swept Wings at a chordbased Reynolds number of Wings due to weakened downwash induced by the tip vortices. With increasing sweep angle, the source of threedimensionality transitions from the tip to the midspan. The threedimensional midspan effects are responsible for the formation of the stationary vortical structures at the inboard part of the span, which expands the steady wake region to higher aspect ratios. At higher aspect ratios, the midspan effects of Swept Wings diminish at the outboard region, allowing unsteady vortex shedding to develop near the tip. In the wakes of highly Swept Wings, streamwise fingerlike structures form repetitively along the wing span, providing a stabilizing effect. The insights revealed from this study can aid the design of highlift devices and serve as a stepping stone for understanding the complex wake dynamics at higher Reynolds numbers and those generated by unsteady wing manoeuvres.