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unsteady-aerodynamics
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Aeroelastic stability and response of composite swept wings in subsonic flow using indicial aerodynamics
, Article Journal of Vibration and Acoustics, Transactions of the ASME ; Volume 135, Issue 5 , 2013 ; 10489002 (ISSN) ; Farsadi, T ; Haddadpour, H ; Sharif University of Technology
2013
Abstract
In this study, the aeroelastic stability and response of an aircraft swept composite wing in subsonic compressible flow are investigated. The composite wing was modeled as an anisotropic thin-walled composite beam with the circumferentially asymmetric stiffness structural configuration to establish proper coupling between bending and torsion. Also, the structural model consists of a number of nonclassical effects, such as transverse shear, material anisotropy, warping inhibition, nonuniform torsional model, and rotary inertia. The finite state form of the unsteady aerodynamic loads have been modeled based on the indicial aerodynamic theory and strip theory in the subsonic compressible flow....
Expansion of indicial function approximations for 2-D subsonic compressible aerodynamic loads
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 1 , 2012 , Pages 519-528 ; 9780791845172 (ISBN) ; Javanshir, J ; Sharif University of Technology
2012
Abstract
This article deals with the new generation of proper Mach dependent exponential approximations of the indicial aerodynamic functions toward the aeroelastic formulation of 2-D lifting surface in the subsonic compressible flow. The indicial lift response is a useful starting point in the development of a general time-domain unsteady aerodynamic theory. By definition, an indicial function is the response to a disturbance that is applied instantaneously at time zero and held constant thereafter; that is a disturbance given by a step function. If the indicial response is known, then the unsteady loads to arbitrary changes in angle of attack can be obtained through the superposition of indicial...
Experimental study of the plunging motion with unsteady wind tunnel wall interference effects
, Article Experimental Techniques ; Volume 36, Issue 5 , FEB , 2012 , Pages 30-45 ; 07328818 (ISSN) ; Marzabadi, F. R ; Mohammadi, Z ; Sharif University of Technology
2012
Abstract
A series of experiments were carried out to investigate unsteady behavior of the flow field as well as the boundary layer of an airfoil oscillating in plunging-type motion in a subsonic wind tunnel. The measurements involved surface-mounted hot films complimented with surface pressure. In addition, wind tunnel wall pressure distribution was acquired to furnish a baseline for the wall interference corrections. The airfoil is the section of a 660-kW wind turbine blade. The experiments were conducted at a Reynolds number of 0.42 million, and over two reduced frequencies of k = 0.06 and 0.085, at prestall, nearstall, and poststall regions. The unsteady aerodynamic loads were calculated from the...
Continuous-time state-space unsteady aerodynamic modeling based on boundary element method
, Article Engineering Analysis with Boundary Elements ; Volume 36, Issue 5 , 2012 , Pages 789-798 ; 09557997 (ISSN) ; Ghadiri, B ; Abdalla, M. M ; Haddadpour, H ; De Breuker, R ; Sharif University of Technology
2012
Abstract
In this paper a continuous-time state-space aerodynamic model is developed based on the boundary element method. Boundary integral equations governing the unsteady potential flow around lifting bodies are presented and modified for thin wing configurations. Next, the BEM discretized problem of unsteady flow around flat wing equivalent to the original geometry is recast into the standard form of a continuous-time state-space model considering some auxiliary assumptions. The system inputs are time derivative of the instantaneous effective angle of attack and thickness/camber correction terms while the outputs are unsteady aerodynamic coefficients. To validate the model, its predictions for...
An efficient method for nonlinear aeroelasticy of slender wings
, Article Nonlinear Dynamics ; Volume 67, Issue 1 , 2012 , Pages 659-681 ; 0924090X (ISSN) ; Sadr, M. H ; Haddadpour, H ; Sharif University of Technology
2012
Abstract
This paper aims the nonlinear aeroelastic analysis of slender wings using a nonlinear structural model coupled with the linear unsteady aerodynamic model. High aspect ratio and flexibility are the specific characteristic of this type of wings. Wing flexibility, coupled with long wingspan can lead to large deflections during normal flight operation of an aircraft; therefore, a wing in vertical/forward-afterward/torsional motion using a third-order form of nonlinear general flexible Euler-Bernoulli beam equations is used for structural modeling. Unsteady linear aerodynamic strip theory based on the Wagner function is used for determination of aerodynamic loading on the wing. Combining these...
Experimental investigation on aerodynamic performance of a flapping wing vehicle in forward flight
, Article Journal of Fluids and Structures ; Volume 27, Issue 4 , 2011 , Pages 586-595 ; 08899746 (ISSN) ; Ebrahimi, A ; Sharif University of Technology
2011
Abstract
The aerodynamic performance of a flexible membrane flapping wing has been investigated here. For this purpose, a flapping-wing system and an experimental set-up were designed to measure the unsteady aerodynamic forces of the flapping wing motion. A one-component force balance was set up to record the temporal variations of aerodynamic forces. The flapping wing was studied in a large low-speed wind tunnel. The lift and thrust of this mechanism were measured for different flapping frequencies, angles of attack and for various wind tunnel velocities. Results indicate that the thrust increases with the flapping frequency. An increase in the wind tunnel speed and flow angle of attack leads to...
Aeroelastic Analysis of Aircraft Composite Wings in a Compressible Flow
, M.Sc. Thesis Sharif University of Technology ; haddadpour, Hassan (Supervisor)
Abstract
In this research, an anistropic thin-walled beam composite is used to consider the effects of fiber orientation and lay-up configuration on the aeroelastic stability and response of an aircraft wing. The circum ferentially asymmetric stiffness (CAS) model consists of a group of non-classical effects; such as transverse shear, material anisotropic, warping inhibition, etc. The aerodynamic load has been modeled based on the strip theory and compressible unsteady flow in the finite- state form. In addition, to form the mass, stiffness and damping matrices of non-conservative aeroelastic systems the extended Galerkin’s method (EGM) and the method of separation of variables has been used. After...
Study of Reduced Frequency Effects on Wind Tunnel Wall Pressure for a Plunging Airfoil
, M.Sc. Thesis Sharif University of Technology ; Soltani, Mohammad Reza (Supervisor)
Abstract
The unsteady phenomena occur in rotors of helicopters, wind turbines and compressors. Investigation of the unsteady flow is a very important test, since it can affect and restrict the performance of rotors of helicopters and wind turbine's blades when operating at high angles of attack. Dynamic tests, such as pitching and plunging oscillations are one of the best methods for studying these phenomena due to the complexity of the unsteady flows. In analyzing the results of dynamic tests one must consider the interference effects of wind tunnel walls. Different investigations show that in dynamic tests, the interference effects of flow field around the model, wind tunnel walls and support of...
Effects of Reduced Frequency and Mean Angle of Attack on Pressure Distribution of a Supercritical Airfoil under Plunging Motion in Low-Subsonic Flow
, M.Sc. Thesis Sharif University of Technology ; Soltani, Mohammad Reza (Supervisor)
Abstract
A ten percent thick supercritical airfoil, having special previllage rather than conventional airfoils tested in a low speed wind tunnel to measure pressure distribution over the airfoil in steady and unsteady flow. Present thesis is set out to discuss effects of reduced frequency and mean angle of attack on pressure distribution during plunging motion in low-subsonic flow. Investigation of experimental data from frequency domain aspect is very challenging area in experimental aerodynamics. Therefore, the concepts of frequency domain analysis is pointed out. The analysis of experiment data is devidind in two different part, that is, steady and unsteady flow. Flow separation over the airfoil...
Experimental study on interaction of aerodynamics with flexible wings of flapping vehicles in hovering and cruise flight
, Article Archive of Applied Mechanics ; Volume 80, Issue 11 , 2010 , Pages 1255-1269 ; 09391533 (ISSN) ; Ebrahimi, A ; Sharif University of Technology
2010
Abstract
Flapping wings are promising lift and thrust generators, especially for very low Reynolds numbers. To investigate aeroelastic effects of flexible wings (specifically, wing's twisting stiffness) on hovering and cruising aerodynamic performance, a flapping-wing system and an experimental setup were designed and built. This system measures the unsteady aerodynamic and inertial forces, power usage, and angular speed of the flapping wing motion for different flapping frequencies and for various wings with different chordwise flexibility. Aerodynamic performance of the vehicle for both no wind (hovering) and cruise condition was investigated. Results show how elastic deformations caused by...
Experimental investigation of the effect of chordwise flexibility on the aerodynamics of flapping wings in hovering flight
, Article Journal of Fluids and Structures ; Volume 26, Issue 4 , May , 2010 , Pages 544-558 ; 08899746 (ISSN) ; Ebrahimi, A ; Sharif University of Technology
2010
Abstract
Ornithopters or mechanical birds produce aerodynamic lift and thrust through the flapping motion of their wings. Here, we use an experimental apparatus to investigate the effects of a wing's twisting stiffness on the generated thrust force and the power required at different flapping frequencies. A flapping wing system and an experimental set-up were designed to measure the unsteady aerodynamic and inertial forces, power usage and angular speed of the flapping wing motion. A data acquisition system was set-up to record important data with the appropriate sampling frequency. The aerodynamic performance of the vehicle under hovering (i.e., no wind) conditions was investigated. The lift and...
Providing Optimization Tools to Design Aeroelastic Blades of Wind Turbines Made of Curved Fibers
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor)
Abstract
Nowadays Aeroelasticity is one of most important branch of aerospace science. The Aeroelastic analysis and get on aeroelastic safety margin, is one of the major steps that must be taken in flying crafts design. Diverse software have been developed for this purpose. Due to the increasing the demands of use of composite materials in aircraft structures, need to examine the effect of various parameters such as angles and stacking sequence on the aeroelastic instability (flutter and divergence) composite aircraft structures is determined. The analysis of wind turbines as a means of extracting energy from the wind and having a large diameter blades, causing the interference effects of aerodynamic...
Unsteady flow over offshore wind turbine airfoils and aerodynamic loads with computational fluid dynamic simulations
, Article International Journal of Environmental Science and Technology ; Volume 13, Issue 6 , 2016 , Pages 1525-1540 ; 17351472 (ISSN) ; Radmanesh, A. R ; Soltani, M. R ; Sharif University of Technology
Center for Environmental and Energy Research and Studies
Abstract
The first notable megawatt class wind turbine, which was the pioneer of improvement in the blade performance in large wind turbines, appeared in Vermont. Nowadays, modern wind turbines are using blades with multi-airfoils at different sections. In this study, in order to indicate the best airfoil profile for the optimum performance in different sections of a blade, five popular airfoils, including S8xx, FFA and AH series, were studied. On the large-scale profile, shear stress transport K–ω model was applied for the simulation of horizontal axis wind turbines for different wind speeds. The aerodynamic simulation was accomplished using computational fluid dynamic method, which in turn is based...
Nonlinear Aeroelastic Analysis of Composite Wing at a Hale Flight Vehicle
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouz-Abadi, Roholla (Supervisor)
Abstract
The purpose of this study is aeroelastic stability analysis and nonlinear aeroelastic vibration of composite wing with nonlinear 1D beam model. Wing’s structure modelled as thin-walled composite single box beam in linear and nonlinear conditions. Thin-walled composite box beam developed by classical lamination theory and structural nonlinearity is von karman strain. Unsteady aerodynamic of wing modelled with modified strip theory. Aeroelastic equations of wing obtained from modal expansion (assumed mode) and Hamilton’s Principle. In order to stability analysis of wing, the linear aeroelastic equations in state space must be calculated and so with eigenvalue analysis instability speed will be...
Effects of Wind Shear Flow on the Aeroelastic Performance of a Large-Scale Wind Turbine with UBEM
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor) ; Taeibi-Rahni, Mohamad (Supervisor) ; Rezaei, Mohamad Mahdi (Co-Supervisor)
Abstract
Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added...
6DOF Flight Dynamics Modeling of a Flexible Flapping wing using Unsteady Aerodynamics
, Ph.D. Dissertation Sharif University of Technology ; Pourtakdoust, Hossein (Supervisor)
Abstract
A complete 6DOF flight dynamic model of an elastic flapping wing (EFW), integrated with unsteady aerodynamic theory is developed. In this respect, initially efficient high fidelity modules for EFW structural dynamics (SD) as well as unsteady aerodynamics loadings (UAL) to be coupled with its flight dynamics are prepared. A modal approach is followed to model structural dynamics of plain and 3D EFWs. This is in contrast with the Euler-Bernoulli beam theory that is mostly utilized for SD in the existing literature. In addition, due to the possibility of large wing deformations as well as the existence of non-linear displacement regime for realistic EFW flights, non-linear modal approaches such...
Aeroelastic Modeling and Stability Analysis of a Flapping Wing with Unsteady Aerodynamic Approach
, M.Sc. Thesis Sharif University of Technology ; Pourtakdoost, Hossein (Supervisor)
Abstract
At this project we proceed to aero elastic modelling of a flapping wing using unsteady aerodynamic approach. Solving this model according to aerodynamic and structure coupling needs to simultaneously solve of aerodynamic and wing structure. Left side and right side of wing, each on divided into 18 elements. each element is interacting with sides element in terms of structural force and moment. In this modeling aerodynamic was modeling with unsteady aerodynamic approach (using modify theodersen function), also structure is flexible in to direction, bending and twisting. In the following it is proved that with change in flapping pattern better performance can be achieved. the effect of change...
Investigation of the Effects of Reduced Frequency and Mean Angle of Attack on the Surface Pressure of a Supercritical Airfoil in Pitching Oscillation
, M.Sc. Thesis Sharif University of Technology ; Soltani, Mohammad Reza (Supervisor)
Abstract
Supercritical airfoils have been designed for transonic flow, however due to different flight conditions, the airfoil behavior during take-off and landing of the aircraft in subsonic flow regime must be known. Experimental and numerical information derived from supercritical airfoils are less than those of conventional airfoils. Because of the special geometry of supercritical airfoils and different phenomena that occurs through flow, using such airfoils even in steady states requires precise study/analysis of the flow. Therefore, one could benefit from experimental tests to better understand flow phenomena. The objective of the present research is the study effect of mean angle of attack...
Unsteady aerodynamic analysis of different multi-MW horizontal axis wind turbine blade profiles on SST K-ω model
, Article Green Energy and Technology ; 2018 , Pages 17-30 ; 18653529 (ISSN) ; Abbaspour, M ; Soltani, M. R ; Sharif University of Technology
Springer Verlag
2018
Abstract
In this study, in order to indicate the best airfoil profile for the different sections of a blade, five airfoils including S8xx, FFA, and AH series were studied. Among the most popular wind power blades for this application were selected, in order to find the optimum performance. Nowadays, modern wind turbines are using blades with multi-airfoils at different sections. On the large scale profile, SST K-ω model with different wind speed at large-scale profile was applied to the simulation of horizontal axis wind turbines (HAWT). The aerodynamic simulation was accomplished using the computational fluid dynamic (CFD) method based on the finite volume method. The governing equations applied in...
Effect of reduced frequency on the aerodynamic behavior of an airfoil oscillating in a plunging motion
, Article Scientia Iranica ; Volume 16, Issue 1 , 2009 , Pages 40-52 ; 10263098 (ISSN) ; Rasi Marzabadi, F ; Sharif University of Technology
2009
Abstract
A series of low speed wind tunnel tests were conducted to study the unsteady aerodynamic behavior of an airfoil sinusoidally oscillating in plunge. The experiments included measuring the surface pressure distribution over a range of reduced frequencies, k = 0.03 - 0.06. In addition, steady state data were acquired and were used to furnish a baseline for further analysis and comparison. The model was oscillated with amplitude of ±15 cm and at three different mean angles of attack of 0, 10° and 18°. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces. The plunging displacements were transformed into...