Aeroelastic Analysis of Membrane Microair Vehicles—Part II: Computational Study of a Plunging Membrane Airfoil

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Peter J. Attar ◽  
Raymond E. Gordnier ◽  
Jordan W. Johnston ◽  
William A. Romberg ◽  
Ramkumar N. Parthasarathy
Keyword(s):  
Strouhal Number ◽  
Stokes Equations ◽  
Computational Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Reduced Frequency ◽  
Lift And Drag ◽  
Intermediate Value

In the second paper of the two part study of membrane microair vehicles, computations are performed for a plunging membrane airfoil. The computational model uses a sixth-order finite difference solution of the Navier–Stokes equations coupled to a finite element solution of a set of nonlinear string equations. The effect, on the structural and fluid response, of plunging Strouhal number, reduced frequency, and static angle of attack is examined. Qualitatively, the flow field is found to be very complex with interactions of vortices shed from various locations along the chord of the airfoil. At a low angle of attack and a low Strouhal number, increasing reduced frequency results in a decrease and an increase in the mean sectional lift and drag coefficients, respectively. Also, at a low angle of attack, increasing the Strouhal number has minimal effect at high and low values of reduced frequencies, but a significant effect is found at an intermediate value of reduced frequency. When the effect of angle of attack is studied for fixed values of Strouhal number and reduced frequency, it is found that the act of plunging gives improved mean sectional lift when compared with the case of a fixed flexible airfoil. The improvement does not increase monotonically with the angle of attack but instead is maximum at an intermediate value. Finally, increasing the value of the membrane prestrain, which stiffens the airfoil, results in a reduced value of the sectional lift coefficient for a given Strouhal number, reduced frequency, and angle of attack.

Stability Analysis of a Light Aircraft Configuration Using Computational Fluid Dynamics

2012 ◽  
Vol 225 ◽  
pp. 391-396 ◽  
Author(s):  
Mohammed Mahdi ◽  
Yasser A. Elhassan
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Rate Of Change ◽  
Navier Stokes ◽  
Rolling Moment ◽  
Moment Coefficient ◽  
Stability Derivatives ◽  
Lift And Drag

This work aims to simulate and study the flow field around SAFAT-01 aircraft using numerical solution based on solving Reynolds Averaged Navier-Stokes equations coupled with K-ω SST turbulent model. The aerodynamics behavior of SAFAT-01 aircraft developed at SAFAT aviation complex were calculated at different angles of attack and side slip angles. The x,y and z forces and moments were calculated at flight speed 50m/s and at sea level condition. Lift and drag curves for different angles of attack were plotted. The maximum lift coefficient for SAFAT-01 was 1.67 which occurred at angle of attack 16° and Maximum lift to drag ratio (L/D) was 14 which occurred at α=3°, and the zero lift drag coefficient was 0.0342. Also the yawing moment coefficient was plotted for different side slip angles as well as rolling moment. The longitudinal stability derivatives with respect to angle of attack, speed variation (u), rate of pitch (q) and time rate of change of angle of attack were calculated using obtained CFD results. Concerning lateral stability only side slips derivatives were calculated. To validate this numerical simulation USAF Digital DATCOM is used to analyze this aircraft; a comparison between predicted results for this aircraft and Digital DATCOM indicated that this numerical simulation has high ability for predicting the aerodynamics characteristics.

scholarly journals Effect of Leading-Edge Bulges on Aerodynamic Characteristics of Bionic Wingsail

2021 ◽  
Author(s):  
Chen Li ◽  
Peiting Sun ◽  
Hongming Wang
Keyword(s):  
Stokes Equations ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Suction Surface ◽  
Ansys Fluent ◽  
Navier Stokes Equations ◽  
Extension Direction ◽  
Lift And Drag

The leading-edge bulges along the extension direction are designed on the marine wingsail. The height and the spanwise wavelength of the protuberances are 0.1c and 0.25c, respectively. At Reynolds number Re=5×105, the Reynolds Averaged Navier-Stokes equations are applied to the simulation of the wingsail with the bulges thanks to ANSYS Fluent finite-volume solver based on the SST K-ω models. The grid independence analysis is carried out with the lift and drag coefficients of the wingsail at AOA = 8° and AOA=20°. The results show that while the efficiency of the wingsail is reduced by devising the leading-edge bulges before stall, the bulges help to improve the lift coefficient of the wingsail when stalling. At AOA=22° under the action of the leading-edge tubercles, a convective vortex is formed on the suction surface of the modified wingsail, which reduces the flow loss. So the bulges of the wingsail can delay the stall.

Spectral Difference Solution of Incompressible Flow Over an Inline Tube Bundle With Oscillating Cylinder

2012 ◽  
Author(s):  
Christopher Cox ◽  
Chunlei Liang ◽  
Michael Plesniak
Keyword(s):  
Forced Oscillation ◽  
Stokes Equations ◽  
Tube Bundle ◽  
Lift Coefficient ◽  
Flow Simulation ◽  
Navier Stokes ◽  
Spectral Difference ◽  
Navier Stokes Equations ◽  
Incompressible Viscous Flow ◽  
Lift And Drag

A high-order spectral difference (SD) method for solving the Navier-Stokes equations on moving, deformable unstructured grids has been developed [1]. In this paper, the SD method and the artificial compressibility method (ACM) are integrated with a dual time-stepping scheme to model unsteady incompressible viscous flow past an inline tube bundle of cylinders equally sized (diameter = d) and spaced (spacing = 2.1*d) over an unstructured grid. Flow simulation results are obtained using a fourth-order space accurate SD method. Two forced oscillation cases are considered; (1) 1st cylinder oscillation and (2) 2nd cylinder oscillation. The Reynolds number used for both cases is 100 and the flow is laminar. Forced oscillation is performed in the tranverse direction, and the subsequent altering of the flow physics of the system is studied. The frequency of vortex shedding behind each cylinder is the same. Root mean square results show that the lift coefficient is greatest for the 4th inline cylinder in both cases. Furthermore, a reduction in both lift and drag coefficients is seen from case (1) to case (2).

scholarly journals Investigating the Effect of Roughness and Stiffness in 2D Aeroelastic Around Oscillatory Airfoil

2020 ◽  
Vol 15 ◽  
Keyword(s):  
Rough Surface ◽  
Smooth Surface ◽  
Stokes Equations ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Simulation Method ◽  
Navier Stokes ◽  
Time Step ◽  
Navier Stokes Equations ◽  
Lift And Drag

In this research, a software has been developed to investigate the effect of roughness and stiffness in twodimensional aeroelastic in unsteady viscous flow around oscillatory airfoil. In this simulation to solve the Navier-Stokes equations, finite volume method has been used in the code with a high resolution scheme for fluid and structure simulation in transonic flows. For this purpose, fluid and structural behavior is solved separately at each time step and the effect of each one on the other is considered. For computing convection term in transonic unsteady compressible flow, high order SBIC (Second and Blending Interpolation Combined) scheme based on discretization of Normalized Variables Diagram (NVD) is used. Here the technique of inlet velocity vector oscillation which is a simpler method in comparison with rather complicated methods such as dynamic mesh is applied. The two-dimensional motion equations are obtained from the Lagrangian equations which are combined with the aerodynamic equations. The results of validation show that the extracted data has a desirable accuracy and had good agreement to experimental data. The FSI results show that, 1: Lift coefficient in smooth surface is more than the rough surface and also the drag coefficient in rough surface is more than the smooth surface, 2: Shock strength is weaker in the rough surface, 3: The shock’s place has moved to leading edge in the rough surface, 4: The number of oscillations in rough surface is reduced, 5:The structural stability of the airfoil when the surface of the airfoil is rough is much greater than smooth surface, 6: Because the density of the air and the amplitude of the oscillations are small and also small effect on the lift and drag coefficients, can be ignored the added mass in this simulation method

Simulation of Unsteady Flow Around a Cylinder

2015 ◽  
Vol 3 (2) ◽  
pp. 28-49
Author(s):  
Ridha Alwan Ahmed
Keyword(s):  
Stokes Equations ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Mean Value ◽  
Navier Stokes ◽  
Cylinder Surface ◽  
Navier Stokes Equations ◽  
Flow Around A Cylinder ◽  
Numerical Grid ◽  
Good Agreement

       In this paper, the phenomena of vortex shedding from the circular cylinder surface has been studied at several Reynolds Numbers (40≤Re≤ 300).The 2D, unsteady, incompressible, Laminar flow, continuity and Navier Stokes equations have been solved numerically by using CFD Package FLUENT. In this package PISO algorithm is used in the pressure-velocity coupling.        The numerical grid is generated by using Gambit program. The velocity and pressure fields are obtained upstream and downstream of the cylinder at each time and it is also calculated the mean value of drag coefficient and value of lift coefficient .The results showed that the flow is strongly unsteady and unsymmetrical at Re>60. The results have been compared with the available experiments and a good agreement has been found between them

scholarly journals Thermochemical Nonequilibrium in Rapidly Expanding Flows of High-Temperature Air

1997 ◽  
Vol 52 (4) ◽  
pp. 358-368 ◽  
Author(s):  
Michio Nishida ◽  
Masashi Matsumotob
Keyword(s):  
High Temperature ◽  
Vibrational Energy ◽  
Stokes Equations ◽  
Computational Study ◽  
Mass Conservation ◽  
Navier Stokes ◽  
Tvd Scheme ◽  
Governing Equations ◽  
Navier Stokes Equations ◽  
Free Jet

Abstract • This paper describes a computational study of the thermal and chemical nonequilibrium occuring in a rapidly expanding flow of high-temperature air transported as a free jet from an orifice into low-density stationary air. Translational, rotational, vibrational and electron temperatures are treated separately, and in particular the vibrational temperatures are individually treated; a multi-vibrational temperature model is adopted. The governing equations are axisymmetric Navier-Stokes equations coupled with species vibrational energy, electron energy and species mass conservation equations. These equations are numerically solved, using the second order upwind TVD scheme of the Harten-Yee type. The calculations were carried out for two different orifice temperatures and also two different orifice diameters to investigate the effects of such parameters on the structure of a nonequilibrium free jet.

scholarly journals Instability of transonic flow past flattened airfoils

2013 ◽  
Vol 3 (4) ◽  
Author(s):  
Alexander Kuzmin
Keyword(s):  
Numerical Modeling ◽  
Transonic Flow ◽  
Stokes Equations ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Flow Simulations ◽  
Flow Past ◽  
Coefficient Versus

AbstractTransonic flow past a Whitcomb airfoil and two modifications of it at Reynolds numbers of the order of ten millions is studied. The numerical modeling is based on the system of Reynolds-averaged Navier-Stokes equations. The flow simulations show that variations of the lift coefficient versus the angle of attack become more abrupt with decreasing curvature of the airfoil in the midchord region. This is caused by an instability of closely spaced local supersonic regions on the upper surface of the airfoil.

Aeroelastic Analysis of Membrane Micro Air Vehicles

2009 ◽  
Author(s):  
Peter J. Attar ◽  
Raymond E. Gordnier ◽  
Jordan W. Johnston ◽  
William A. Romberg ◽  
Ramkumar N. Parthasarathy
Keyword(s):  
Strouhal Number ◽  
Limit Cycle ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Micro Air Vehicles ◽  
Element Model ◽  
Wing Membrane ◽  
Reduced Frequency ◽  
Membrane Wing ◽  
Air Vehicles

The fluid and structural response of two different membrane wing Micro Air Vehicles is studied through computation and experiment. A (three) batten-reinforced fixed wing membrane micro air vehicle is used to determine the effect of membrane prestrain and fixed angle of attack on flutter and limit cycle behavior of fixed wing membrane Micro Air Vehicles. For each configuration tested, flutter and subsequent limit cycle oscillations are measured in wind tunnel tests and predicted using an aeroelastic computational model consisting of a nonlinear finite element model coupled to a vortex lattice solution of the Laplace equation and boundary conditions. Correlation between the predicted and measured onset of limit cycle oscillation is good as is the prediction of the amplitude of the limit cycle at the trailing edge of the lower membrane. A direct correlation between levels of strain and the phase of the membranes during the limit cycle is found in the computation and thought to also occur in the experiment. The second membrane wing micro air vehicle configuration is that of a plunging membrane airfoil model. This model is studied computationally using a sixth-order finite difference solution of the Navier-Stokes equations coupled to a nonlinear string finite element model. The effect, on the structural and fluid response, of plunging Strouhal number, reduced frequency and static angle of attack is examined. At two degree angle of attack, and Strouhal number of 0.2, the effect of increasing the plunging reduced frequency is to decrease the sectional lift coefficient and increase the sectional drag coefficient. At this angle of attack, minimal change in the sectional lift coefficient is found when increasing from a Strouhal number of 0.2 to 0.5 at reduced frequencies of 0.5 and 5.903, the lowest and highest values of this parameter which are studied in this work. For this angle of attack the maximum change which occurs when increasing the Strouhal number from 0.2 to 0.5 is at a reduced frequency of 1.5. When the effect of angle of attack is studied, it is found that at a Strouhal number of 0.5 and reduced frequency of 1.5 the plunging flexible model demonstrates improved lift characteristics over the fixed flexible airfoil case. The greatest improvement occurs at an angle of attack of 2 degrees followed by 10 degrees and then 6 degrees. Finally the effect on the flow characteristics of airfoil flexibility is investigated by increasing the membrane pre-strain from a nominal value of 5 percent to that of 20 percent. This increase in pre-strain results in a reduced value of sectional lift coefficient as compared the 5 percent pre-strain case at the same fixed angle of attack, Strouhal number and reduced frequency.

The Low Reduced Frequency Limit of Vibrating Airfoils: Part II — Numerical Experiments

2015 ◽  
Author(s):  
Almudena Vega ◽  
Roque Corral
Keyword(s):  
Stokes Equations ◽  
Unsteady Aerodynamics ◽  
Mean Value ◽  
Navier Stokes ◽  
Influence Coefficient ◽  
Navier Stokes Equations ◽  
Unsteady Pressure ◽  
Reduced Frequency ◽  
Influence Coefficients ◽  
Frequency Regime

This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced frequency regime with special emphasis in its impact on the scaling of the work per cycle curves using an asymptotic approach (Part I) and numerical simulations. A perturbation analysis of the linearized Navier-Stokes equations at low reduced frequency is presented and some conclusions are drawn (Part I of the corresponding paper). The first important result is that the loading of the airfoil plays an essential role in the trends of the phase and modulus of the unsteady pressure field caused by the vibration of the airfoil. For lightly loaded airfoils the unsteady pressure and the influence coefficients scale linearly with the reduced frequency whereas the phase departs from π/2 and changes linearly with the reduced frequency. As a consequence the work-per-cycle is proportional to the reduced frequency for any inter-blade phase angle and it is independent of its sign. For highly loaded airfoils the unsteady pressure modulus is fairly constant exhibiting only a small correction with the reduced frequency, while the phase departs from zero varies linearly with it. In this case only the mean value of the work-per-cycle scales linearly with the reduced frequency. This behavior is independent of the geometry of the airfoil and in first approximation of the mode-shape. For symmetric cascades the work-per-cycle scales linearly with the reduced frequency irrespectively of whether the airfoil is loaded or not. Simulations using a frequency domain linearized Navier-Stokes solver have been carried out on a low-pressure turbine airfoil section, the NACA0012 and NACA65 profiles and a flat plate operating at different flow conditions to show the generality and correctness of the analytical conclusions. Both the traveling-wave and influence coefficient formulations of the problem are used in combination to increase the understanding and explore the nature of the unsteady pressure perturbations.

scholarly journals Active Control of a Stalled Airfoil Through Steady or Unsteady Actuation Jets

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
V. G. Chapin ◽  
E. Benard
Keyword(s):  
Active Control ◽  
Computational Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Position Angle ◽  
Navier Stokes ◽  
Suction Surface ◽  
Parametric Studies ◽  
Naca 0012

The active control of the leading-edge (LE) separation on the suction surface of a stalled airfoil (NACA 0012) at a Reynolds number of 106 based on the chord length is investigated through a computational study. The actuator is a steady or unsteady jet located on the suction surface of the airfoil. Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations are solved on hybrid meshes with the Spalart–Allmaras turbulence model. Simulations are used to characterize the effects of the steady and unsteady actuation on the separated flows for a large range of angle of attack (0 < α < 28 deg). Parametric studies are carried out in the actuator design-space to investigate the control effectiveness and robustness. An optimal actuator position, angle, and frequency for the stalled angle of attack α = 19 deg are found. A significant increase of the lift coefficient is obtained (+ 84% with respect to the uncontrolled reference flow), and the stall is delayed from angle of attack of 18 deg to more than 25 deg. The physical nonlinear coupling between the actuator position, velocity angle, and frequency is investigated. The critical influence of the actuator location relative to the separation location is emphasized.

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