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Dr. Kiran Rameshn
Aerospace Sciences Division, School of Engineering, University of Glasgow, Glasgow G12 8QQ, Scotland, UK

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Research Keywords & Expertise

0 dynamic stall
0 Unsteady Aerodynamics
0 Fluid–structure interaction
0 Vortex Particle Methods
0 Flapping flight

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Original article
Published: 31 July 2021 in Theoretical and Computational Fluid Dynamics
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Frequency-domain unsteady lifting-line theory (ULLT) provides a means by which the aerodynamics of oscillating wings may be studied at low computational cost without neglecting the interacting effects of aspect ratio and oscillation frequency. Renewed interest in the method has drawn attention to several uncertainties however. Firstly, to what extent is ULLT practically useful for rectangular wings, despite theoretical limitations? And secondly, to what extent is a complicated wake model needed in the outer solution for good accuracy? This paper aims to answer these questions by presenting a complete ULLT based on the work of Sclavounos, along with a novel ULLT that considers only the streamwise vorticity and a Prandtl-like pseudosteady ULLT. These are compared to Euler CFD for cases of rectangular wings at multiple aspect ratios and oscillation frequencies. The results of this work establish ULLT as a low computational cost model capable of accounting for interacting finite-wing and oscillation frequency effects and identify the aspect ratio and frequency regimes where the three ULLTs are most accurate. This research paves the way towards the construction of time-domain or numerical ULLTs which may be augmented to account for nonlinearities such as flow separation.

ACS Style

Hugh J. A. Bird; Kiran Ramesh. Unsteady lifting-line theory and the influence of wake vorticity on aerodynamic loads. Theoretical and Computational Fluid Dynamics 2021, 1 -23.

AMA Style

Hugh J. A. Bird, Kiran Ramesh. Unsteady lifting-line theory and the influence of wake vorticity on aerodynamic loads. Theoretical and Computational Fluid Dynamics. 2021; ():1-23.

Chicago/Turabian Style

Hugh J. A. Bird; Kiran Ramesh. 2021. "Unsteady lifting-line theory and the influence of wake vorticity on aerodynamic loads." Theoretical and Computational Fluid Dynamics , no. : 1-23.

Journal article
Published: 14 January 2020 in Journal of Fluid Mechanics
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Unsteady thin-aerofoil theory is a low-order method for calculating the forces and moment developed on a camber line undergoing arbitrary motion, based on potential-flow theory. The vorticity distribution is approximated by a Fourier series, with a special ‘ $A_{0}$ ’ term that is infinite at the leading edge representing the ‘suction peak’. Though the integrated loads are finite, the pressure and velocity at the leading edge in this method are singular owing to the $A_{0}$ term. In this article, the principle of matched asymptotic expansions is used to resolve the singularity and obtain a uniformly valid first-order solution. This is performed by considering the unsteady thin-aerofoil theory as an outer solution, unsteady potential flow past a parabola as an inner solution, and by matching them in an intermediate region where both are asymptotically valid. Resolution of the leading-edge singularity allows for derivation of the velocity at the leading edge and location of the stagnation point, which are of physical and theoretical interest. These quantities are seen to depend on only the $A_{0}$ term in the unsteady vorticity distribution, which may be interpreted as an ‘effective unsteady angle of attack’. The leading-edge velocity is proportional to $A_{0}$ and inversely proportional to the square root of leading-edge radius, while the chordwise stagnation-point location is proportional to the square of $A_{0}$ and independent of the leading-edge radius. Closed-form expressions for these in simplified scenarios such as quasi-steady flow and small-amplitude harmonic oscillations are derived.

ACS Style

Kiran Ramesh. On the leading-edge suction and stagnation-point location in unsteady flows past thin aerofoils. Journal of Fluid Mechanics 2020, 886, 1 .

AMA Style

Kiran Ramesh. On the leading-edge suction and stagnation-point location in unsteady flows past thin aerofoils. Journal of Fluid Mechanics. 2020; 886 ():1.

Chicago/Turabian Style

Kiran Ramesh. 2020. "On the leading-edge suction and stagnation-point location in unsteady flows past thin aerofoils." Journal of Fluid Mechanics 886, no. : 1.

Conference paper
Published: 06 January 2019 in AIAA Scitech 2019 Forum
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ACS Style

Hugh J. Bird; Shuji Otomo; Kiran Kumar Ramesh; Ignazio Maria Viola. A Geometrically Non-Linear Time-Domain Unsteady Lifting-Line Theory. AIAA Scitech 2019 Forum 2019, 1 .

AMA Style

Hugh J. Bird, Shuji Otomo, Kiran Kumar Ramesh, Ignazio Maria Viola. A Geometrically Non-Linear Time-Domain Unsteady Lifting-Line Theory. AIAA Scitech 2019 Forum. 2019; ():1.

Chicago/Turabian Style

Hugh J. Bird; Shuji Otomo; Kiran Kumar Ramesh; Ignazio Maria Viola. 2019. "A Geometrically Non-Linear Time-Domain Unsteady Lifting-Line Theory." AIAA Scitech 2019 Forum , no. : 1.

Journal article
Published: 06 October 2018 in Journal of Fluids and Structures
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The nonlinear dynamics of an airfoil at Reynolds number Re=10,000 constrained by two springs and subject to a uniform oncoming flow is studied numerically. The studies are carried out using open source computational fluid dynamics toolbox OpenFOAM. Under certain conditions related to aerodynamic flutter, this two-degree-of-freedom system undergoes self-sustained limit-cycle oscillations (LCOs) with potential application as an energy harvester. When the system is given a small initial perturbation, it is seen that the response of the system decays to zero at flow velocities below the flutter velocity, or oscillates in a limit cycle at velocities greater than the flutter velocity. The flutter velocity at Re=10,000 is shown to deviate significantly from the theoretical prediction (which is derived with an assumption of infinite Reynolds number) owing to the effect of viscosity. The LCOs at freestream velocities higher than the flutter velocity result in unsteady flows that are heavily influenced by leading-edge vortex shedding as well as trailing-edge flow separation. The influence of different system parameters on the onset of flutter and on the limit-cycle response characteristics is investigated in this research. This is done by defining a baseline case and examining the effects of varying aerodynamic parameters such as freestream velocity, and structural parameters such as the pitch-to-plunge frequency ratio and the type of spring stiffnesses. The conditions corresponding to the lowest flutter velocities (and consequently the lowest “cut-in” speeds for power extraction) and the parameter space that provide single-period, single-amplitude and harmonic LCOs (ideal for power extraction) are identified. Calculation of instantaneous and time-averaged power is presented by modeling the extraction of energy through a viscous damper. The highest power coefficients and efficiencies are obtained at velocities just higher than the flutter velocity. Introduction of positive cubic stiffening in the system springs is seen to make the system more stable, LCOs more harmonic and single-period, and to potentially increase power extraction efficiency of the system.

ACS Style

Enhao Wang; Kiran Ramesh; Shaun Killen; Ignazio Maria Viola. On the nonlinear dynamics of self-sustained limit-cycle oscillations in a flapping-foil energy harvester. Journal of Fluids and Structures 2018, 83, 339 -357.

AMA Style

Enhao Wang, Kiran Ramesh, Shaun Killen, Ignazio Maria Viola. On the nonlinear dynamics of self-sustained limit-cycle oscillations in a flapping-foil energy harvester. Journal of Fluids and Structures. 2018; 83 ():339-357.

Chicago/Turabian Style

Enhao Wang; Kiran Ramesh; Shaun Killen; Ignazio Maria Viola. 2018. "On the nonlinear dynamics of self-sustained limit-cycle oscillations in a flapping-foil energy harvester." Journal of Fluids and Structures 83, no. : 339-357.

Original article
Published: 14 August 2017 in Theoretical and Computational Fluid Dynamics
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A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil–Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements.

ACS Style

Kiran Ramesh; Kenneth Granlund; Michael V. Ol; Ashok Gopalarathnam; Jack R. Edwards. Leading-edge flow criticality as a governing factor in leading-edge vortex initiation in unsteady airfoil flows. Theoretical and Computational Fluid Dynamics 2017, 32, 109 -136.

AMA Style

Kiran Ramesh, Kenneth Granlund, Michael V. Ol, Ashok Gopalarathnam, Jack R. Edwards. Leading-edge flow criticality as a governing factor in leading-edge vortex initiation in unsteady airfoil flows. Theoretical and Computational Fluid Dynamics. 2017; 32 (2):109-136.

Chicago/Turabian Style

Kiran Ramesh; Kenneth Granlund; Michael V. Ol; Ashok Gopalarathnam; Jack R. Edwards. 2017. "Leading-edge flow criticality as a governing factor in leading-edge vortex initiation in unsteady airfoil flows." Theoretical and Computational Fluid Dynamics 32, no. 2: 109-136.

Conference paper
Published: 10 June 2016 in 34th AIAA Applied Aerodynamics Conference
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ACS Style

Arun Vishnu Suresh Babu; Kiran Kumar Ramesh; Ashok Gopalarathnam. Model Reduction in Discrete Vortex Methods for 2D Unsteady Aerodynamic Flows. 34th AIAA Applied Aerodynamics Conference 2016, 1 .

AMA Style

Arun Vishnu Suresh Babu, Kiran Kumar Ramesh, Ashok Gopalarathnam. Model Reduction in Discrete Vortex Methods for 2D Unsteady Aerodynamic Flows. 34th AIAA Applied Aerodynamics Conference. 2016; ():1.

Chicago/Turabian Style

Arun Vishnu Suresh Babu; Kiran Kumar Ramesh; Ashok Gopalarathnam. 2016. "Model Reduction in Discrete Vortex Methods for 2D Unsteady Aerodynamic Flows." 34th AIAA Applied Aerodynamics Conference , no. : 1.

Journal article
Published: 01 May 2015 in Journal of Fluids and Structures
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ACS Style

Kiran Ramesh; Joseba Murua; Ashok Gopalarathnam. Limit-cycle oscillations in unsteady flows dominated by intermittent leading-edge vortex shedding. Journal of Fluids and Structures 2015, 55, 84 -105.

AMA Style

Kiran Ramesh, Joseba Murua, Ashok Gopalarathnam. Limit-cycle oscillations in unsteady flows dominated by intermittent leading-edge vortex shedding. Journal of Fluids and Structures. 2015; 55 ():84-105.

Chicago/Turabian Style

Kiran Ramesh; Joseba Murua; Ashok Gopalarathnam. 2015. "Limit-cycle oscillations in unsteady flows dominated by intermittent leading-edge vortex shedding." Journal of Fluids and Structures 55, no. : 84-105.

Conference paper
Published: 03 January 2015 in 53rd AIAA Aerospace Sciences Meeting
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ACS Style

Kiran Kumar Ramesh; Jack R. Edwards; Christopher P. Goyne; James C. McDaniel. Large Eddy Simulation of High-Speed, Premixed Ethylene Combustion (Invited). 53rd AIAA Aerospace Sciences Meeting 2015, 1 .

AMA Style

Kiran Kumar Ramesh, Jack R. Edwards, Christopher P. Goyne, James C. McDaniel. Large Eddy Simulation of High-Speed, Premixed Ethylene Combustion (Invited). 53rd AIAA Aerospace Sciences Meeting. 2015; ():1.

Chicago/Turabian Style

Kiran Kumar Ramesh; Jack R. Edwards; Christopher P. Goyne; James C. McDaniel. 2015. "Large Eddy Simulation of High-Speed, Premixed Ethylene Combustion (Invited)." 53rd AIAA Aerospace Sciences Meeting , no. : 1.

Journal article
Published: 23 June 2014 in Journal of Fluid Mechanics
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Unsteady aerofoil flows are often characterized by leading-edge vortex (LEV) shedding. While experiments and high-order computations have contributed to our understanding of these flows, fast low-order methods are needed for engineering tasks. Classical unsteady aerofoil theories are limited to small amplitudes and attached leading-edge flows. Discrete-vortex methods that model vortex shedding from leading edges assume continuous shedding, valid only for sharp leading edges, or shedding governed by ad-hoc criteria such as a critical angle of attack, valid only for a restricted set of kinematics. We present a criterion for intermittent vortex shedding from rounded leading edges that is governed by a maximum allowable leading-edge suction. We show that, when using unsteady thin aerofoil theory, this leading-edge suction parameter (LESP) is related to the $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}A_0$ term in the Fourier series representing the chordwise variation of bound vorticity. Furthermore, for any aerofoil and Reynolds number, there is a critical value of the LESP, which is independent of the motion kinematics. When the instantaneous LESP value exceeds the critical value, vortex shedding occurs at the leading edge. We have augmented a discrete-time, arbitrary-motion, unsteady thin aerofoil theory with discrete-vortex shedding from the leading edge governed by the instantaneous LESP. Thus, the use of a single empirical parameter, the critical-LESP value, allows us to determine the onset, growth, and termination of LEVs. We show, by comparison with experimental and computational results for several aerofoils, motions and Reynolds numbers, that this computationally inexpensive method is successful in predicting the complex flows and forces resulting from intermittent LEV shedding, thus validating the LESP concept.

ACS Style

Kiran Ramesh; Ashok Gopalarathnam; Kenneth Granlund; Michael V. Ol; Jack R. Edwards. Discrete-vortex method with novel shedding criterion for unsteady aerofoil flows with intermittent leading-edge vortex shedding. Journal of Fluid Mechanics 2014, 751, 500 -538.

AMA Style

Kiran Ramesh, Ashok Gopalarathnam, Kenneth Granlund, Michael V. Ol, Jack R. Edwards. Discrete-vortex method with novel shedding criterion for unsteady aerofoil flows with intermittent leading-edge vortex shedding. Journal of Fluid Mechanics. 2014; 751 ():500-538.

Chicago/Turabian Style

Kiran Ramesh; Ashok Gopalarathnam; Kenneth Granlund; Michael V. Ol; Jack R. Edwards. 2014. "Discrete-vortex method with novel shedding criterion for unsteady aerofoil flows with intermittent leading-edge vortex shedding." Journal of Fluid Mechanics 751, no. : 500-538.

Conference paper
Published: 22 June 2013 in 31st AIAA Applied Aerodynamics Conference
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ACS Style

Kiran Kumar Ramesh; Ashok Gopalarathnam; Jack R. Edwards; Kenneth O. Granlund; Michael V. Ol. Theoretical Analysis of Perching and Hovering Maneuvers. 31st AIAA Applied Aerodynamics Conference 2013, 1 .

AMA Style

Kiran Kumar Ramesh, Ashok Gopalarathnam, Jack R. Edwards, Kenneth O. Granlund, Michael V. Ol. Theoretical Analysis of Perching and Hovering Maneuvers. 31st AIAA Applied Aerodynamics Conference. 2013; ():1.

Chicago/Turabian Style

Kiran Kumar Ramesh; Ashok Gopalarathnam; Jack R. Edwards; Kenneth O. Granlund; Michael V. Ol. 2013. "Theoretical Analysis of Perching and Hovering Maneuvers." 31st AIAA Applied Aerodynamics Conference , no. : 1.

Journal article
Published: 16 January 2013 in Theoretical and Computational Fluid Dynamics
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An inviscid theoretical method that is applicable to non-periodic motions and that accounts for large amplitudes and non-planar wakes (large-angle unsteady thin airfoil theory) is developed. A pitch-up, hold, pitch-down motion for a flat plate at Reynolds number 10,000 is studied using this theoretical method and also using computational (immersed boundary method) and experimental (water tunnel) methods. Results from theory are compared against those from computation and experiment which are also compared with each other. The variation of circulatory and apparent-mass loads as a function of pivot location for this motion is examined. The flow phenomena leading up to leading-edge vortex shedding and the limit of validity of the inviscid theory in the face of vortex-dominated flows are investigated. Also, the effect of pitch amplitude on leading-edge vortex shedding is examined, and two distinctly different vortex-dominated flows are studied using dye flow visualizations from experiment and vorticity plots from computation.

ACS Style

Kiran Ramesh; Ashok Gopalarathnam; Jack R. Edwards; Michael V. Ol; Kenneth Granlund. An unsteady airfoil theory applied to pitching motions validated against experiment and computation. Theoretical and Computational Fluid Dynamics 2013, 27, 843 -864.

AMA Style

Kiran Ramesh, Ashok Gopalarathnam, Jack R. Edwards, Michael V. Ol, Kenneth Granlund. An unsteady airfoil theory applied to pitching motions validated against experiment and computation. Theoretical and Computational Fluid Dynamics. 2013; 27 (6):843-864.

Chicago/Turabian Style

Kiran Ramesh; Ashok Gopalarathnam; Jack R. Edwards; Michael V. Ol; Kenneth Granlund. 2013. "An unsteady airfoil theory applied to pitching motions validated against experiment and computation." Theoretical and Computational Fluid Dynamics 27, no. 6: 843-864.

Conference paper
Published: 25 June 2012 in 30th AIAA Applied Aerodynamics Conference
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ACS Style

Kiran Kumar Ramesh; Ashok Gopalarathnam; Kenneth Granlund; Michael Ol; Jack Edwards. Theoretical Modeling of Leading Edge Vortices Using the Leading Edge Suction Parameter. 30th AIAA Applied Aerodynamics Conference 2012, 1 .

AMA Style

Kiran Kumar Ramesh, Ashok Gopalarathnam, Kenneth Granlund, Michael Ol, Jack Edwards. Theoretical Modeling of Leading Edge Vortices Using the Leading Edge Suction Parameter. 30th AIAA Applied Aerodynamics Conference. 2012; ():1.

Chicago/Turabian Style

Kiran Kumar Ramesh; Ashok Gopalarathnam; Kenneth Granlund; Michael Ol; Jack Edwards. 2012. "Theoretical Modeling of Leading Edge Vortices Using the Leading Edge Suction Parameter." 30th AIAA Applied Aerodynamics Conference , no. : 1.

Conference paper
Published: 25 June 2012 in 30th AIAA Applied Aerodynamics Conference
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ACS Style

Kiran Ramesh; Jianghua Ke; Ashok Gopalarathnam; Jack Edwards. Effect of Airfoil Shape and Reynolds Number on Leading Edge Vortex Shedding in Unsteady Flows. 30th AIAA Applied Aerodynamics Conference 2012, 1 .

AMA Style

Kiran Ramesh, Jianghua Ke, Ashok Gopalarathnam, Jack Edwards. Effect of Airfoil Shape and Reynolds Number on Leading Edge Vortex Shedding in Unsteady Flows. 30th AIAA Applied Aerodynamics Conference. 2012; ():1.

Chicago/Turabian Style

Kiran Ramesh; Jianghua Ke; Ashok Gopalarathnam; Jack Edwards. 2012. "Effect of Airfoil Shape and Reynolds Number on Leading Edge Vortex Shedding in Unsteady Flows." 30th AIAA Applied Aerodynamics Conference , no. : 1.

Conference paper
Published: 14 June 2011 in 41st AIAA Fluid Dynamics Conference and Exhibit
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ACS Style

Kiran Kumar Ramesh; Ashok Gopalarathnam; Michael Ol; Kenneth Granlund; Jack Edwards. Augmentation of Inviscid Airfoil Theory to Predict and Model 2D Unsteady Vortex Dominated Flows. 41st AIAA Fluid Dynamics Conference and Exhibit 2011, 1 .

AMA Style

Kiran Kumar Ramesh, Ashok Gopalarathnam, Michael Ol, Kenneth Granlund, Jack Edwards. Augmentation of Inviscid Airfoil Theory to Predict and Model 2D Unsteady Vortex Dominated Flows. 41st AIAA Fluid Dynamics Conference and Exhibit. 2011; ():1.

Chicago/Turabian Style

Kiran Kumar Ramesh; Ashok Gopalarathnam; Michael Ol; Kenneth Granlund; Jack Edwards. 2011. "Augmentation of Inviscid Airfoil Theory to Predict and Model 2D Unsteady Vortex Dominated Flows." 41st AIAA Fluid Dynamics Conference and Exhibit , no. : 1.

Conference paper
Published: 04 January 2011 in 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition
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ACS Style

Kiran Ramesh; Ashok Gopalarathnam; Jack Edwards; Michael Ol; Kenneth Granlund. Theoretical, Computational and Experimental Studies of a Flat Plate Undergoing High-Amplitude Pitching Motion. 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2011, 1 .

AMA Style

Kiran Ramesh, Ashok Gopalarathnam, Jack Edwards, Michael Ol, Kenneth Granlund. Theoretical, Computational and Experimental Studies of a Flat Plate Undergoing High-Amplitude Pitching Motion. 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. 2011; ():1.

Chicago/Turabian Style

Kiran Ramesh; Ashok Gopalarathnam; Jack Edwards; Michael Ol; Kenneth Granlund. 2011. "Theoretical, Computational and Experimental Studies of a Flat Plate Undergoing High-Amplitude Pitching Motion." 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition , no. : 1.