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Sunetra Sarkar

Bio: Sunetra Sarkar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Airfoil & Polynomial chaos. The author has an hindex of 16, co-authored 95 publications receiving 819 citations. Previous affiliations of Sunetra Sarkar include Delft University of Technology & Indian Institute of Science.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a systematic understanding of the influence of various parameters on thrust generation from an aharmonically pitching airfoil is presented, which is very similar to the inviscid theory prediction, however, in a clear deviation from inviscidian theorytrends, pitching at high amplitudes about high mean angle of attack, only drag is observed for high values of reduced frequency considered.

40 citations

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TL;DR: In this article, numerical simulations of a heaving airfoil undergoing non-sinusoidal motions in an incompressible viscous flow are presented, and the wake patterns, thrust force coefficients, and propulsive efficiency at various values of non-dimensional heave velocity are computed.
Abstract: Numerical simulations of a heaving airfoil undergoing non-sinusoidal motions in an incompressible viscous flow is presented In particular, asymmetric sinusoidal motions, constant heave rate oscillations, and sinusoidal motions with a quiescent gap, are considered The wake patterns, thrust force coefficients, and propulsive efficiency at various values of non-dimensional heave velocity are computed These have been compared with those of corresponding sinusoidal heaving motions of the airfoil It is shown that for a given non-dimensional heave velocity and reduced frequency of oscillation, asymmetric sinusoidal motions give better thrust and propulsive efficiencies in comparison to pure harmonic motion On the other hand, constant rate heave motion do not compare favourably with harmonic motion A train of sinusoidal pulses separated by a quiescent gap compares favourably with a pure sinusoidal motion, but with the notable exception that the quiescent gap induces a discontinuity that induces large impulses to the wake pattern

39 citations

Journal ArticleDOI
TL;DR: In this article, the transition in aeroelastic response from an initial state characterised by low-amplitude aperiodic fluctuations to aero-elastic flutter when the system exhibits limit cycle oscillations was studied.

37 citations

Journal ArticleDOI
TL;DR: In this article, a nonlinear aeroelastic system with parametric uncertainties is considered, and a projection-based nonintrusive polynomial chaos approach is shown to be much faster than its classical Galerkin method based counterpart.
Abstract: Aeroelastic stability remains an important concern for the design of modern structures such as wind turbine rotors, more so with the use of increasingly flexible blades. A nonlinear aeroelastic system has been considered in the present study with parametric uncertainties. Uncertainties can occur due to any inherent randomness in the system or modeling limitations, and so forth. Uncertainties can play a significant role in the aeroelastic stability predictions in a nonlinear system. The analysis has been put in a stochastic framework, and the propagation of system uncertainties has been quantified in the aeroelastic response. A spectral uncertainty quantification tool called Polynomial Chaos Expansion has been used. A projection-based nonintrusive Polynomial Chaos approach is shown to be much faster than its classical Galerkin method based counterpart. Traditional Monte Carlo Simulation is used as a reference solution. Effect of system randomness on the bifurcation behavior and the flutter boundary has been presented. Stochastic bifurcation results and bifurcation of probability density functions are also discussed.

33 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of the pitch angle of an airfoil on its near field vortex structure and aerodynamic loads during a dynamic stall process was analyzed at low to medium reduced frequencies with the maximum angle of attack not exceeding 25°.
Abstract: This study presents the influence of pitch angle of an airfoil on its near-field vortex structure as well as the aerodynamic loads during a dynamic stall process. Dynamic stall behavior in a sinusoidally pitching airfoil is usually analyzed at low to medium reduced frequencies and with the maximum angle of attack of the airfoil not exceeding 25°. In this work, we study dynamic stall of a symmetric airfoil at medium to high reduced frequencies even as the maximum angle of attack goes from 25° to 45°. The evolution and growth of the laminar separation bubble, also known as a dynamic stall vortex, at the leading edge and the trailing edge are studied as the pitch cycle goes from the minimum to the maximum angle of attack. The effect of reduced frequencies on the vortex structure as well as the aerodynamic load coefficients is investigated. The reduced frequency is shown to be a bifurcation parameter triggering period doubling behavior. However, the bifurcation pattern is dependent on the variation of the pitch angle of incidence of the airfoil.

28 citations


Cited by
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Journal ArticleDOI
TL;DR: A non intrusive method that builds a sparse PC expansion, which may be obtained at a reduced computational cost compared to the classical ''full'' PC approximation.

1,112 citations

01 Jan 2007
TL;DR: Two algorithms for generating the Gaussian quadrature rule defined by the weight function when: a) the three term recurrence relation is known for the orthogonal polynomials generated by $\omega$(t), and b) the moments of the weightfunction are known or can be calculated.
Abstract: Most numerical integration techniques consist of approximating the integrand by a polynomial in a region or regions and then integrating the polynomial exactly. Often a complicated integrand can be factored into a non-negative ''weight'' function and another function better approximated by a polynomial, thus $\int_{a}^{b} g(t)dt = \int_{a}^{b} \omega (t)f(t)dt \approx \sum_{i=1}^{N} w_i f(t_i)$. Hopefully, the quadrature rule ${\{w_j, t_j\}}_{j=1}^{N}$ corresponding to the weight function $\omega$(t) is available in tabulated form, but more likely it is not. We present here two algorithms for generating the Gaussian quadrature rule defined by the weight function when: a) the three term recurrence relation is known for the orthogonal polynomials generated by $\omega$(t), and b) the moments of the weight function are known or can be calculated.

1,007 citations

01 Jan 2006
TL;DR: The mysterious rattleback and its fluid counterpart:Developments in shear instabilities(Patrick Huerre,Falling clouds+Elisabeth Guazzelli)LEcotectural fluid mechanics%Herbert Huppert )
Abstract: 流体力学杂志“Journal of Fluid Mechanics”由剑桥大学教授George Batchelor在1956年5月创办,在国际流体力学界享有很高的学术声望,被公认为是流体力学最著名的学术刊物之一,2005年的影响因子为2.061,雄居同类期刊之首.在它创刊50周年之际,2006年5月JFM出版了第554卷的纪念特刊,其中刊登了现任主编(美国西北大学S.H.Davis教授和英国剑桥大学T.J.Pedley教授)合写的述评:“Editorial:JFM at50”,以JFM为背景,从独特的视角对近50年来流体力学的发展进行了简明的回顾和展望,并归纳了一系列非常有启发性的有趣统计数字.2006年7月21日在剑桥大学应用数学和理论物理研究所(DAMTP)举行了创刊50周年的庆祝会.下午2点,JFM的新老编辑和来宾会聚一堂,Pedley教授致开幕词,其后是5个精彩的报告:The mysterious rattleback and its fluid counterpart(Keith Moffatt),Developments in shear instabilities(Patrick Huerre),Falling clouds(Elisabeth Guazzelli),Ecotectural fluid mechanics(Paul Linden),The success of JFM(Herbert Huppert),最后由Davis教授致闭幕词.

767 citations

01 Jul 1994
TL;DR: In this article, the effects of large computational time steps on the computed turbulence were investigated using a fully implicit method in turbulent channel flow computations and the largest computational time step in wall units which led to accurate prediction of turbulence statistics was determined.
Abstract: Effects of large computational time steps on the computed turbulence were investigated using a fully implicit method. In turbulent channel flow computations the largest computational time step in wall units which led to accurate prediction of turbulence statistics was determined. Turbulence fluctuations could not be sustained if the computational time step was near or larger than the Kolmogorov time scale.

470 citations

Journal ArticleDOI
TL;DR: The key idea is to align the complexity level and order of analysis with the reliability and detail level of statistical information on the input parameters to avoid the necessity to assign parametric probability distributions that are not sufficiently supported by limited available data.

350 citations