Now showing 1 - 10 of 15
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    Unsteady aerodynamics of multiple airfoils in configuration
    (01-01-2011)
    Aziz, Hossain
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    A lumped vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady flow past two airfoils in configuration, each of which is impulsively set into motion. The unsteady wakes of both airfoils are modeled by discrete vortices and timestepping is used to predict the individual wake shapes. The coupled flow is solved using a combined "zero-normal flow" boundary condition and Kelvin condition which results in (2N +2)X(2N+2) equations. Results are presented showing the effect of airfoil-airfoil and airfoilwake interaction on the aerodynamic characteristics of the configuration for the airfoils moving with zero and non-zero relative velocity. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
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    A numerical study of the unsteady motion of a wing using N-body approximation
    (01-01-2014)
    Vasanth Kumar, G.
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    Numerical simulation of unsteady motion of wing through undisturbed fluid is formulated using Unsteady Vortex Lattice Method. Singularities in the form of vortex ring elements are distributed over the surface of the wing mean camber and remain fixed in space. The wake vortex ring singularities are free to deform under the action of velocity field induced by the combination of moving wing and deforming wake vortex ring elements. CL, CDi, Г distribution etc., are calculated for different cases of unsteady motion. A free-wake algorithm is developed based on the higher order numerical integration schemes. Minimum cut-off distance to avoid r-1numerical singularity is obtained from Rankine vortex model. No-normal ow boundary condition is imposed over the surface of mean camber and the resulting MN × MN equations are solved for Г using LU decomposition.
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    Behaviour of trailing wing(s) in echelon formation due to wing twist and aspect ratio
    (01-04-2017)
    Gunasekaran, M.
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    In this paper, a novel decambering technique has been implemented using a vortex lattice method to study the effects of wing twist on the induced drag of individual lifting surfaces in configuration flight including post-stall angles of attack. The effect of both geometric and aerodynamic twist is studied. In the present work, 2D data of NACA0012 airfoil from XFoil at Re=1×106 is used to predict 3D post-stall data using geometric twist for a single wing and compared with literature. The effect of aerodynamic twist is implemented by using different airfoils along wing–span and the resulting wing CL–α and Cdi–α are compared with experiment. Study of wings of different aspect ratios with & without aerodynamic twist on both leading and trailing wings helps to understand the effect of twist on the lift and induced drag when they are varied on both wings simultaneously and individually.
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    High-Alfa Aerodynamics with Separated Flow Modeled as a Single Nascent Vortex
    (11-04-2017)
    Antony, Samuel B.
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    A numerical iterative vortex lattice method is developed to study flow past wing(s) at high angles of attack where the separated flow is modelled using NY nascent vortex filaments. The wing itself is modelled using NX × NY bound vortex rings, where NX and NY are the number of sections along the chord and span of the wing respectively. The strength and position of the nascent vortex along the chord corresponding to the local effective angle of attack are evaluated from the residuals in viscous and potential flow, i.e. (Cl)visc - (Cl)pot and (Cm)visc - (Cm)pot. Hence, the 2D airfoil viscous Cl - α and Cm - α is required as input (from experiment, numerical analysis or CFD). Aerodynamic characteristics and section distribution along span are predicted for 3D wings at a high angle of attack. Effect of initial conditions and existence of multiple solutions in the post-stall region is studied. Results are validated with experiment.
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    A numerical study of tandem pitching airfoils
    (19-08-2013)
    Shirsath, Ravindra A.
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    Aziz, Hossain
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    A lumped vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady flow past tandem pitching airfoils. The unsteady wakes of both airfoils are modeled by discrete vortices and time-stepping is used to predict the individual wake shapes. The coupled flow is solved using a combined "zero-normal flow" boundary condition and Kelvin condition which results in (2N+2)X(2N+2) equations. Commercial software FLUENT is also used to study the flow tandem pitching airfoils. Results are presented showing the effect of airfoil-airfoil and airfoil-wake interaction on the aerodynamic characteristics of the tandem airfoils pitching in or out of phase and also when only the leading airfoil pitches and the trailing airfoil is stationary. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
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    A numerical study of the aerodynamics of Cessna 172 aircrafts in echelon formation
    (01-01-2014)
    Gunasekaran, M.
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    A vortex-lattice numerical scheme that uses a novel decambering technique to predict post-stall aerodynamic characteristics is used to study the aerodynamics of tandem Cessna 172 aircrafts flying in echelon formation. Results like CL- α from the current method are compared with experiment. Additional results like section Cldistributions over wing spans, CM- α and CLW- αtw(i.e. CLof the leading aircraft for different angles of attack of the trailing aircraft) and analysis for (-) ve y-offset, which are available only from the current numerical method are reported that supplement the experimental results. Detailed post-stall numerical analysis and the effect of chord-wise, span-wise and vertical offsets on the aerodynamics of the formation are also reported.
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    Development of Flow over Blunt-Nosed Slender Bodies at Transonic Mach Numbers
    (11-04-2017)
    Yanamashetti, Gireesh
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    Suryanarayana, G. K.
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    Comparisons of the development of flow over a cylinder with a 20° cone nose and a cylinder with an ogive nose, which represent typical heat-shield configurations are studied using CFD and experiments at transonic Mach numbers. The Cp plots are studied to locate expansion or separation. Experiments are carried out at M = 0.8, 0.9, 0.95 and 1.1 and Re ≈ 2.45 × 106. Computations are carried out using the commercial package, FLUENT 6.3. Inadequate spatial resolution of pressure ports in experiments as well as limitations of the CFD tool result in some differences in experimental and CFD results.
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    Prediction of post-stall aerodynamic characteristics of wing(S) with separated flow modeled as a single nascent vortex
    (01-01-2016)
    Samuel, Antony B.
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    A numerical iterative vortex lattice method is developed for post-stall flow past wing(s) where the separated flow is modeled using NY nascent vortex flaments. The wing itself is modeled using NX x NY bound vortex rings, where NX and NY are the number of sections along the chord and span of the wing respectively. The strength and position of the nascent vortex along the chord corresponding to the local e_ective angle of attack are evaluated from the residuals in viscous and potential ow, i.e. (Cl)visc– (Cl)potand (Cm)visc– (Cm)pot. Hence, the 2D airfoil viscous Cl– α and Cm– α is required as input (from experiment, numerical analysis or CFD). Aerodynamic characteristics and section distribution along span are predicted for 3D wings at post-stall angles of attack. Effect of initial conditions and existence of multiple solutions in the post-stall region is studied. Results are validated with experiment.
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    Publication
    Vortex interaction and roll-up in unsteady flow past tandem airfoils
    (01-01-2016)
    Aziz, H.
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    A discrete vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady flow past two airfoils in configuration. The unsteady wakes of the airfoils are modeled by discrete vortices and time-stepping is used to predict the individual wake shapes. The coupled flow is solved using a combined zeronormal flow boundary condition and Kelvin condition which result in (2N + 2)X(2N + 2) equations. Results are presented showing the effect of airfoil-airfoil and airfoil-wake interaction on the aerodynamic characteristics of the configuration. The effect of relative velocity, rate of pitching and phase-lag are studied on airfoil performance and wake shape is predicted.
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    Publication
    A numerical study of the unsteady motion of a wing using N-body approximation
    (01-01-2014)
    Vasanth Kumar, G.
    ;
    Numerical simulation of unsteady motion of wing through undisturbed uid is formulated using Unsteady Vortex Lattice Method. Singularities in the form of vortex ring elements are distributed over the surface of the wing mean camber and remain fixed in space. The wake vortex ring singularities are free to deform under the action of velocity field induced by the combination of moving wing and deforming wake vortex ring elements. CL, CDi, γ distribution etc., are calculated for different cases of unsteady motion. A free-wake algorithm is developed based on the higher order numerical integration schemes. Minimum cut-off distance to avoid r-1 numerical singularity is obtained from Rankine vortex model. No-normal flow boundary condition is imposed over the surface of mean camber and the resulting MN × MN equations are solved for γ using LU decomposition.