Showing papers on "Pitching moment published in 2019"

Transverse Vibration Response of a Super High-Speed Elevator under Air Disturbance

Abstract: For a super high-speed elevator running in a hoistway, it will encounter air flows at high speed. The transverse force and pitching moment generated by the air intensify the transverse vibration of...

Parameter optimization for improved aerodynamic performance of louver-type wind barrier for train-bridge system

Abstract: To improve the safety of trains running in an undesirable wind environment, a novel louver-type wind barrier is proposed and further studied in this research using a scaled wind tunnel simulation with 1:40 scale models. Based on the aerodynamic performance of the train-bridge system, the parameters of the louver-type wind barrier are optimized. Compared to the case without a wind barrier, it is apparent that the wind barrier improves the running safety of trains, since the maximum reduction of the moment coefficient of the train reaches 58% using the louver-type wind barrier, larger than that achieved with conventional wind barriers (fence-type and grid-type). A louver-type wind barrier has more blade layers, and the rotation angle of the adjustable blade of the louver-type wind barrier is 90–180° (which induces the flow towards the deck surface), which is more favorable for the aerodynamic performance of the train. Comparing the 60°, 90° and 120° wind fairings of the louver-type wind barrier blade, the blunt fairing is disadvantageous to the operational safety of the train.

Investigation of the aerodynamic performance and flow physics on cross sections of Dragonfly wing on flapping and pitching motion in low Reynolds number

Abstract: In this research, the flow physics and aerodynamic performance of dragonfly cross sections, used in Micro Aerial Vehicles (MAVs), in low Reynolds are investigated. The main objective of the researc...

Numerical simulation of laser energy discharge for flight control

Abstract: The numerical investigation of the interaction of an off-axis laser discharge in front of an ogive cylinder at Mach 3.4 is presented. Details of the physics of the interaction of the blast wave and heated region with the ogive cylinder shock structure and the effect of this interaction on the drag, side force and pitching moment are included. The location of laser discharge and the amount of energy added to the gas by the laser are two main factors affecting the flow. Increasing the energy absorbed by the gas increases the drag reduction, the desired side force and pitching moment. Increasing the distance of the discharge from the axis reduces both drag reduction and side force achieved by the laser discharge.

Energy extraction properties of a flapping wing with a deformable airfoil

Abstract: Flapping wing devices have attracted considerable attention as a new means of power extraction. The present study applies transient numerical calculations based on the dynamic mesh technique to investigate the influences of leading edge, trailing edge, or overall circular arc airfoil deformations on the power extraction efficiencies of a flapping wing device under the condition of maintaining a constant arc length along the mean camber line of the foil. The results indicate that airfoil deformations can improve the power extraction efficiency of the flapping wing device. The primary reason is that the active synchronised deformation of the foil increases the effective curvature and the velocity circulation around the foil. In addition, the performance curve of the flapping wing device exhibits two frequency ranges with relative high efficiency. In the low frequency region, if the leading edge vortex (LEV) detaches from the trailing edge just as the foil reverses its heaving direction, the foil will gain much more energy due to the positive power extraction of the pitching moment. In the high frequency region, a small steady body-attached vortex (BAV) maintains a high lift, and, thus, the device extracts more power due to the enhanced heaving force.

Numerical prediction of aerodynamic performance for a flying fish during gliding flight.

Abstract: Flying fish is a family of unique aerial-aquatic animals, which can both swim in the water and glide over the sea surface. Most previous studies on their aerodynamic characteristics were based on field observations or measurements of their morphometric parameters. In the present study, we consider three different flying fish models, of which the preliminary one mimics the Cypselurus hiraii in the pectoral fin morphology, following a previous wind tunnel experiment (Park and Choi 2010 J. Exp. Biol. 213 3269-79). Their aerodynamic performances are numerically studied by the computational fluid dynamics (CFD) method. The maximum lift force coefficient of 1.03 is reached at the angle of attack [Formula: see text], and the maximum lift-to-drag ratio of 4.7 is achieved at [Formula: see text]. By choosing appropriately the center of gravity, the flying fish model is proved to be longitudinally stable, according to the negative slope of pitching moment profile. Furthermore, we build a three-degrees-of-freedom (3-DOF) dynamic model in the longitudinal plane based on the aerodynamic coefficients obtained in our simulations, to predict its gliding performance. The results show that the flying fish can achieve a distance up to 45.4 m, and reach a height of 13.2 m, indicating an extraordinary gliding performance. Our numerical simulations are consistent with previous experimental results and theoretical prediction, which can be taken as the basis of further research on robotic flying fish.

Evaluating the Influence of Unsteady Air Density to the Aerodynamic Performance of a Fixed Wing Aircraft at different angle of attack Using Computational Fluid Dynamics

Abstract: Recent studies have focused on unsteady aerodynamics of an aircraft using computational fluid dynamics. It was found that a change in the density of air within the flight domain influences the aerodynamic performance of aircrafts in flight. This is as a result of the occurrence of turbulence and unsteadiness in the air velocity vectors. Limited work has focused on the impact of transient change in the density of air to lift, drag and moment coefficient acting on the aircraft fuselage during flight. This paper is aimed at determining how the unsteadiness in the density of air influences the aerodynamic performance of an aircraft with time. To determine the aerodynamic performance of an aircraft within this unsteady airflow condition, lift, drag coefficient and the wing design efficiency was used as the deterministic parameter for the investigation. A compressible simulation was performed for transonic flows with Mach number 0.84. The wing geometry was designed using SOLIDWORKS and the CFD simulation was performed using ANSYS Fluent version 18.1 software. A User Defined Function (UDF) was developed using a MATLAB code. This was aimed at, to introduce a time-dependent change in the density of air, in the Fluent environment. Results obtained showed that a 0.24 average change in air density caused a drop in lift coefficient by an amount 0.01014. The wing design efficiency achieved in this study was 56% and this value is low. Therefore, a change in the density of air will cause the aircraft to observe a poor aerodynamic behavior and eventually stall.

Comparison of Iced Aerodynamic Measurements on a Swept Wing from Two Wind Tunnels

Abstract: Artificial ice shapes of various geometric fidelity were tested on a wing model based on the Common Research Model. Low Reynolds number tests were conducted at Wichita State University's Beech Memorial Wind Tunnel, and high Reynolds number tests were conducted at ONERA's F1 wind tunnel. The aerodynamic performance data from the two facilities were compared at matched or similar Reynolds and Mach number to ensure that the results and trends observed at low Reynolds number could be applied and continued to high Reynolds number. For both clean and iced configurations, the data from Wichita State University and F1 agreed well at matched or similar Reynolds and Mach numbers. The lift and pitching moment curves agreed very well for most configurations. There appeared to be 0.2-0.3deg offset in the angle of attack between the Wichita State University and F1 data, possibly due to different flow angularities in the test sections of the two facilities. There was also an offset in the drag values between the two facilities from an unknown cause. Overall, the data compared very well between the low Reynolds number test at Wichita State University tunnel and the high Reynolds number test at F1. This indicated that data from the low Reynolds number tests could be used to understand iced-swept-wing aerodynamics at high Reynolds number.

Aerodynamic Performance of an Aircraft Equipped with Horizontal Tail-Mounted Propellers

Abstract: This paper presents an experimental and numerical study of the aerodynamic interaction between horizontal tail-mounted propellers and the airframe. A representative aircraft model was installed in a low-speed wind-tunnel and measurements were taken with an external balance to determine the effect of propeller installation on integral forces and moments. Total pressure measurements were performed downstream of the model for qualitative analysis of the propeller–airframe interaction. The experimental data were complemented by full blade CFD analyses, which correlate excellently to the experimental data. Balance measurements indicate that the propeller installation results in an offset and a change in the slope of the pitching moment curve over the complete range of angles of attack. The extent to which the propellers contribute to the longitudinal control and stability was shown to be dependent on the angle of attack of the aircraft and the rotation direction of the propellers. The flowfield and computed propeller loads show that an inboard-up rotating propeller results in a neutral contribution to longitudinal stability towards higher angles of attack, while an outboard-up rotation enhances the stability for all positive angles of attack. The non-uniform inflow to the propeller induced by the airframe leads to a lateral shift of the thrust which influences the trim condition.

Experimental Analysis of a Wind-Turbine Rotor Blade Airfoil by means of Temperature-Sensitive Paint

Abstract: Knowledge on the boundary-layer transition location at large chord Reynolds numbers (Re ≥ 3 million) is essential to evaluate the performance of airfoils designed for modern wind-turbine rotor blades, which rotor diameters can be of the order of hundred meters. In the present work, a temperature-sensitive paint (TSP) was used to systematically study boundary-layer transition on the suction side of a DU 91-W2-250 airfoil. The experiments were performed in the High-Pressure Wind Tunnel Gottingen at chord Reynolds numbers up to Re = 12 million and angles-of-attack from -14° to 20°. The coefficients of airfoil lift, drag, and pitching moment were also obtained after integration of the pressure distributions measured on the wind-tunnel model surface and in the model wake. The surface data obtained by means of TSP enabled not only to analyze the evolution of the transition location with varying angle-of-attack and chord Reynolds number, but also to provide an explanation for the evolution of the aerodynamic coefficients measured at stall and post-stall conditions. The stability of the laminar boundary layers investigated in the experiments was analyzed according to linear stability theory. The results of the stability computations supported the experimentally observed variations in the transition location. The amplification factors of boundary-layer disturbances at transition were also determined by correlating the experimental and numerical results.

Aerodynamic design of integrated propulsion–airframe configuration of a hybrid wing body aircraft

Abstract: A hybrid wing body (HWB) concept is being considered by NASA as a potential subsonic transport aircraft that meets aerodynamic, fuel, emission, and noise goals in the time frame beyond 2035. While the concept promises advantages over a conventional wing-and-tube aircraft, it poses unknowns and risks, thus requiring in-depth and broad assessments. Specifically, the configuration entails a tight integration of the airframe and propulsion geometries; the aerodynamic impact has to be carefully evaluated. With the propulsion nacelle installed on the (upper) body, the lift and drag are affected by the mutual interference effects between the airframe and nacelle. The static margin for longitudinal stability is also adversely changed. In the present paper, a design approach is developed in which the integrated geometries of airframe (HWB) and propulsion are accounted for simultaneously in a simple algebraic manner, via parameterization of the planform and airfoils at the design sections of the wing body. This paper presents a design of a 300-passenger aircraft that employs distributed electric fans for the propulsion. The trim condition for stability is achieved through the use of the wing tip twist angle. The geometric shape variables are determined through the adjoint optimization method by minimizing the drag while subjecting them to lift, pitching moment, and geometry constraints. An Euler model-based aerodynamic shape optimization is employed to save the design cost for the evaluation of the static margin and longitudinal stability, while the performance of the optimized configuration is evaluated by the RANS model coupled with a drag decomposition method to assess the true aerodynamic performance. The design results clearly show the influence on the aerodynamic characteristics of the installed nacelle and trimming for stability. A drag minimization with the trim constraint yields a reduction of 10 counts in the drag coefficient from the baseline design N3-X configuration, which is comparable with 2000 lbs more payload on a conventional subsonic civil transport airplane.

Coupled Computational Fluid Dynamics and Comprehensive Analysis Calculations of a Gimballed Tiltrotor

Abstract: In an effort to assess the suitability of the HPCMP CREATE-AV™ Helios computational tool for calculating tiltrotor aeromechanics characteristics, comparisons of rotor performance, blade pitch, and ...

Numerical Analysis of Leading-Edge Vortex Effect on Tidal Current Energy Extraction Performance for Chord-Wise Deformable Oscillating Hydrofoil

Abstract: To improve the energy extraction performance of the oscillating hydrofoil, the lift force that acts on the oscillating hydrofoil is analyzed. The pressure difference between the oscillating hydrofoil‘s opposing surfaces is dominant to generate the lift force. Forming and shedding of the leading-edge vortex from the hydrofoil surface determines the pressure difference between the opposing surfaces of the oscillating hydrofoil. In this paper, the hydrofoil with different chord flexibility coefficients and maximum offset at the trailing edge are analyzed to obtain the power coefficient, lift coefficient, and moment coefficient of the oscillating hydrofoil. The influence mechanism of chord-wise deformation of the oscillating hydrofoil on the energy extraction performance is explored. According to the Kutta–Joukowsky condition and the Stokes’ theorem, the relationship between the attached vortex on the hydrofoil and the surface pressure of the hydrofoil, the surface pressure difference of the hydrofoil, and the lift force that acts on the hydrofoil are investigated. By quantifying the vortex intensity, the ascending-shedding process of the attached vortex on the hydrofoil is characterized. Finally, the complete influence chain among the chord-wise flexure, the attached vortex on the hydrofoil, and the energy extraction performance of the oscillating hydrofoil is established.

Effect of Gurney Flap Geometry on a S809 Airfoil

Abstract: In this paper, the effect of Gurney flap shapes on wind turbine blade airfoil S809 has been studied by numerical simulation. First, the O-type grid is used in the numerical simulation. By comparing with experimental data, such as the lift force, the drag coefficient, and the pressure distribution, the accuracy of the simulation method is validated. Second, the research on the widths of three kinds of rectangular Gurney flaps at the trailing edge of the S809 airfoil is carried out. Rectangular Gurney flaps can considerably increase the lift in both the linear and nonlinear sections, and the maximum lift coefficient can be increased by 20.65%. In addition, the drag and the pitching moment are increased. However, the width of the rectangular Gurney flap has a small impact on the lift, the drag, and the pitching moment. Finally, the effects of rectangular and triangular Gurney flaps on the aerodynamic characteristics of the S809 airfoil are compared. The results show that the triangular flaps can obtain an increase of maximum lift coefficient by 28.42%, which is better than 16.31% of the rectangular flaps.

A trapezoidal wing equivalent to a Janatella leucodesma’s wing in terms of aerodynamic performance in the flapping flight of a butterfly model

Abstract: Wing planform is one of the most important factors for lift and thrust generation and enhancement in flapping flight. In a previous study based on a simple numerical model of a butterfly, we found that the wing planform of an actual butterfly (Janatella leucodesma) is more efficient than any rectangular or trapezoidal wing planform. In the present study, we make a hypothesis that the efficient aerodynamic performance of a butterfly's wings can be reproduced by the following four geometrical parameters of wing planform: aspect ratio, taper ratio, position of the rotational axis for the geometric angle of attack, and sweepback angle. In order to test this hypothesis, we explore a trapezoidal wing planform equivalent to an actual butterfly's wing planform in terms of aerodynamic performance in a parameter space consisting of these four parameters. We use a simple butterfly model composed of two rigid thin wings and a rod-shaped body and calculate the aerodynamic performance of the model by an immersed boundary-lattice Boltzmann method to find such a trapezoidal wing planform. As a result, we find a trapezoidal wing planform which gives almost the same lift, thrust, pitching moment, power, and power-loading coefficients as an actual butterfly's wing planform. Furthermore, in the free flight of the butterfly model with pitching motion control, the flight behavior of the model with the resulting trapezoidal wing planform is almost the same as that with an actual butterfly's wing planform.

Subcritical Limit Cycle in Airfoil Aeroelastic System with Freeplay: Prediction and Mechanism

Abstract: This paper investigates the aeroelastic system of an airfoil with freeplay in pitch, with emphasis on the subcritical limit cycle (LC) that appears below the linear flutter velocity. The lowest flo...

Computational Analysis of the External Aerodynamics of the Unpowered X-57 Mod-III Aircraft

Abstract: Investigations of the external aerodynamics of the unpowered X-57 Mod-III configuration using computational fluid dynamics are presented. Two different Reynolds-averaged Navier-Stokes flow solvers were used in the analysis: the STAR-CCM+ unstructured solver using polyhedral grid topology, and the Launch Ascent Vehicle Aerodynamics (LAVA) structured curvilinear flow solver using structured overset grid topology. A grid refinement study was conducted and suitable grid resolution was determined by examining the forces and moments of the aircraft. Code-to-code comparison shows that STAR-CCM+ and LAVA are in good agreement both in quantitative values and trends. The angle-of-attack sweep and sideslip-angle sweep were performed. Results indicate that lift coefficients have a sharp drop at stall. At high angle of attack, STAR-CCM+ and LAVA show different flow separation behavior possibly due to differences in the turbulence model. The sideslip-angle sweep results show constant pitching moment from 0° to 15°, then a sharp increase between 15° and 20° sideslip angle.

Unsteady Computational Study of Novel Biologically Inspired Offshore Vertical Axis Wind Turbine at Different Tip Speed Ratios: A Two-Dimensional Study

Abstract: The aim of this paper presents an unsteady numerical investigation of a novel biologically inspired vertical axis wind turbine. The simulation was conducted in 2D using the sliding mesh technique with non-conformal mesh spatial discretisation via FLUENT. Grid sensitivity study on mesh density and turbulent transport model indicated that fine mesh and medium converged well with trivial difference. SST and k-ω model presented stable behaviour and indicated good agreement. SST were chosen for the rest of the simulation. The proposed wind turbine was simulated at five different moderate tip speed ratios under the influence of freestream velocity U∞=8m/s. The highest moment coefficient is generated at tip speed ratio λ=1.3, which is Cm=0.1886 with a stable positive moment coefficient after 480°. The proposed turbine responded well at λ=1.3 and λ=1.7 with power coefficient result of Cp=0.245 and Cp=0.262 respectively. The effect of wake and voracity on the turbine at subjected tip speed ratios is studied. Wake regions induced by the leading edge of the aerofoil impacted the performance of the following blade. Furthermore, due to the less wake effect trailed by the leading edge at λ=1.3, it generates higher moment than λ=1.7. Since the proposed blade has a fixed 4° angle of attack, it was sensible for the turbine to experience such wake and vorticity effect.

Developments of a semiempirical dynamic stall model for unsteady airfoils

Abstract: A new semiempirical dynamic stall model is presented to predict the aerodynamic coefficients of an airfoil in unsteady conditions. The model is mainly based on two modifications on the airfoil angle of attack which introduce an equivalent angle of attack to implement in the proposed aerodynamic coefficients. The first modification includes unsteady wake effects of the airfoil in the proposed model which are not considered in most of the semiempirical models. Hence, an effective angle of attack is introduced based on an unsteady aerodynamic theory using the Wagner function for pitching and plunging oscillations of the airfoil. The second modification takes into account time delay effects and dynamic effects due to the flow separation on the airfoil. These effects are included in the model by developing a semiempirical relationship between static and dynamic angle of attack published in the literature. Finally, the modifications form the equivalent angle of attack to implement in a set of equations based on Kirchhoff flow theory. The proposed approach dynamically approximates trailing edge separation point on the airfoil by a completely new way and contributes its effects in the aerodynamic coefficients. Moreover, apparent mass effects and the airfoil leading edge vortex contributions are sufficiently included in the model. The presented method effectively predicts unsteady lift and pitching moment coefficients of the airfoil undergoing stall conditions. Consequently, the proposed model is verified against experimental data under various test cases where obtained numerical results are in good agreement with the test data. Furthermore, the performance of the proposed model is compared with various dynamic stall models including Leishman–Beddoes model, ONERA model and Boeing–Vertol model. The comparison shows that the proposed model minimizes the number of the semiempirical parameters determined from an experiment in dynamic stall modeling compared with Leishman–Beddoes model and ONERA model. It also demonstrates that the presented model performs as well as other well-known models using the various approaches.