Papers by Shreyas Ananthan
Journal of the American Helicopter Society, 2006
Page 1. Rotor Wake Aerodynamics in Large Amplitude Maneuvering Flight Shreyas Ananthan ∗ J. Gordo... more Page 1. Rotor Wake Aerodynamics in Large Amplitude Maneuvering Flight Shreyas Ananthan ∗ J. Gordon Leishman Graduate Research Assistant Minta Martin ... N ∗Corresponding author; email: [email protected]. Presented ...
The problem of helicopter rotor wake aerodynamics during maneuvering flight conditions was analyz... more The problem of helicopter rotor wake aerodynamics during maneuvering flight conditions was analyzed using a time-accurate, free-vortex wake methodology. The free-vortex method consists of a Lagrangian representation of the rotor flow field using vortex elements, where the evolution of the flow field is simulated by tracking the free motion of these vortex elements and calculating their induced velocity field. Traditionally, free-vortex methods are inviscid, incompressible models, but in the present approach the viscous effects are incorporated using a viscous splitting method where the viscous and inviscid terms are modeled as successive sub-processes. The rotor aerodynamics and rigid blade flapping dynamics are closely coupled with the wake model and solved for in a consistent manner using the same numerical scheme.
This paper presents a study of three flight maneuvers using a rotorcraft aeroacoustics model: &qu... more This paper presents a study of three flight maneuvers using a rotorcraft aeroacoustics model: "pop-up," "pop-down," and an arrested descent. A time-accurate free-vortex rotor wake model and a maneuvering rotor noise prediction code were used to compute the noise. All ro-torcraft motions and rigid body blade motions were in-cluded in the respective models. The wake geometry and its development is described. It is shown that the magni-tude and directivity of the noise is strongly dependent on the rotor wake characteristics when blade-vortex interac-tions occur. In the transient arrested descent maneuver, the wake geometry becomes extremely complicated, and a significant increase in both nonimpulsive and impulsive noise is predicted.
A loosely-coupled CFD-CSD aeroelastic analysis was conducted to study the feasibility of using tr... more A loosely-coupled CFD-CSD aeroelastic analysis was conducted to study the feasibility of using trailing edge flaps (TEFs) for alleviating the adverse effects of dynamic stall on UH-60A rotor performance. The coupled simulation framework was rigorously validated against available flight test data (flight counter C9017 a high- altitude, high-thrust flight condition at a moderate advance ratio with a distinct dynamic stall event on the retreating side of the rotor disk). It was observed that the increased effective camber of the rotor airfoil section, together with a nose-down pitching moment induced by the downward deflection of the TEFs can serve to delay the onset of dynamic stall and, therefore, can mitigate the severity of the resulting stall event. Results from the parametric study show that, with the right phasing and amplitude, a harmonic excitation of the TEFs can greatly reduce the magnitude of the stall that occurs at a given flight condition. Predictions further show that t...
50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2009
This paper predicts, analyzes, and validates main rotor airloads, structural loads, and swashplat... more This paper predicts, analyzes, and validates main rotor airloads, structural loads, and swashplate servo loads in a prescribed high-g pull-up maneuver. A multibody finite element structural model is coupled to a transient lifting-line aerodynamic model. The structural model includes a ...
19th AIAA Computational Fluid Dynamics, 2009
In our earlier work, 1 we have developed the software named CHIMPS (Coupler for Highperformance I... more In our earlier work, 1 we have developed the software named CHIMPS (Coupler for Highperformance Integrated Multi-Physics Simulations) which facilitates a multi-code coupling procedure by automating the search, interpolation, communication, and data/information transfer in a user-friendly and scalable manner. In this paper, we describe two newly extended capabilities of CHIMPS: One is the full support for the hole-cutting process for unstructured overset-mesh simulations in a parallel environment, and the other is a higher-order interpolation on unstructured meshes. The Cartesian hole-map method is implemented to CHIMPS for an efficient hole cutting. A test using the actual rotor meshes shows that the present implementation leads to a good scalability with a reasonable choice of hole-map resolution. Actual overset-mesh computations also confirm the accuracy of the newly extended capabilities. On the other hand, a serial application of univariate Hermite interpolation is also incorporated to CHIMPS, which shows a third-order formal accuracy on general unstructured elements.
26th AIAA Applied Aerodynamics Conference, 2008
Journal of the American Helicopter Society, 2011
Abstract: This paper isolates the physics governing the aerodynamics and structural dynamics of U... more Abstract: This paper isolates the physics governing the aerodynamics and structural dynamics of UH-60A rotor in an unsteady maneuvering flight and proposes a hypothesis for the mechanism of advancing blade stall observed during pull-up maneuvers. The ...
Journal of the American Helicopter Society, 2008
Page 1. An Optimum Coaxial Rotor System for Axial Flight J. Gordon Leishman ∗Shreyas Ananthan Min... more Page 1. An Optimum Coaxial Rotor System for Axial Flight J. Gordon Leishman ∗Shreyas Ananthan Minta Martin Professor of Engineering Assistant Research Scientist Department of Aerospace Engineering Glenn L. Martin ...
Journal of the American Helicopter Society, 2008
A Computational Study of Helicopter Rotor Wakes and Noise Generated During Transient Maneuvers Hs... more A Computational Study of Helicopter Rotor Wakes and Noise Generated During Transient Maneuvers Hsuan-nien Chen Kenneth S. Brentner ∗ Shreyas Ananthan J. Gordon Leishman Graduate Research Assistant Professor Graduate Research Assistant Minta Martin Professor ...
Journal of the American Helicopter Society, 2004
Journal of the American Helicopter Society, 2004
Page 1. The Vortex Ring State as a Spatially and Temporally Developing Wake Instability J. Gordon... more Page 1. The Vortex Ring State as a Spatially and Temporally Developing Wake Instability J. Gordon Leishman Mahendra J. Bhagwat ∗ Shreyas Ananthan Professor Graduate Research Assistant Graduate Research Assistant ...
Journal of the American Helicopter Society, 2005
Page 1. Predictions of Rotor Performance in Ground Effect Using a Free-Vortex Wake Model Daniel A... more Page 1. Predictions of Rotor Performance in Ground Effect Using a Free-Vortex Wake Model Daniel A. Griffiths ∗ Shreyas Ananthan J. Gordon Leishman Graduate Research Assistant Graduate Research Assistant Minta Martin ...
Journal of Aircraft, 2010
This paper predicts and analyzes main rotor airloads, structural loads, and swashplate servo load... more This paper predicts and analyzes main rotor airloads, structural loads, and swashplate servo loads in a prescribed high-g pull-up maneuver. A multibody finite-element structural model is coupled with a transient lifting-line aerodynamic model. The structural model includes a swashplate model to calculate servo loads. The lifting-line model combines airfoil tables, a Weissinger-L near-wake time-marching free wake, and a semiempirical dynamic stall model. The maneuver data were taken from the Army/NASA UH-60A Airloads Program Flight Counter 11029. The primary objective of this paper is to isolate the effects of structural dynamics, free wake, dynamic stall, and pitch control angles in order to determine the key loads mechanisms in this flight. The structural loads are first calculated using airloads measured in flight. The measured airloads are then replaced with a lifting-line coupled analysis, which is ideally suited to isolate the effects of free wake and dynamic stall. It is concluded that the maneuver is almost entirely dominated by stall, with little or no wake-induced effect on blade loads, even though the wake cuts through the disk twice during the maneuver. At the peak of the maneuver, almost 75% of the operating envelope of a typical airfoil lies beyond stall. The mechanism of dynamic stall, in the analysis, consists of multiple cycles within a wide disk area. The peak-to-peak structural loads prediction from the lifting-line analysis shows an underprediction of 10-20% in flap and chord bending moments and 50% in torsion loads. The errors stem from the prediction of fourand five-revolution stall loads. Swashplate dynamics appear to have a significant impact on the servo loads (unlike in level flight), with a more than 50% variation in peak loads.
Journal of Aircraft, 2004
ABSTRACT \A time-accurate, free-vortex method was used to predict the evolution of a helicopter r... more ABSTRACT \A time-accurate, free-vortex method was used to predict the evolution of a helicopter rotor wake and the corresponding unsteady rotor airloads in response to time-varying changes in blade pitch. Both steady and maneuvering flight conditions were examined. The modeling was validated using measured rotor responses to transient increases in collective pitch and also for oscillatory collective and cyclic blade pitch inputs. In each case the results showed that there was a temporal lag in the growth and convection of vorticity into the rotor wake, causing significant unsteady effects at the rotor. For transient blade pitch inputs the calculated results showed the bundling of individual vortex filaments below the rotor into vortex rings, a result also verified experimentally. These vortex rings, however, subsequently break down through the development of Kelvin waves. A simulated piloted pull-up maneuver from descending flight was studied, producing evidence that maneuvers can also cause wake vorticity to bundle below the rotor Large unsteady rotor airloads were produced as the blades encountered this accumulated wake vorticity. A study was also conducted to examine the effects of small-amplitude, low-frequency blade pitch inputs, typical of pilot control inputs during flight. Overall, it is apparent that even moderate control inputs can have a significant impact on the temporal developments of the rotor wake.
The UH-60A Utility Tactical Transport Aerial System (UTTAS) pull up maneuver was simulated using ... more The UH-60A Utility Tactical Transport Aerial System (UTTAS) pull up maneuver was simulated using a time-accurate, coupled CFD-CSD-free wake analysis. The CFD solver (OVERTURNS) was coupled with a parallel free-vortex wake solver (PWAM) and a structural dynamics solver (UMARC2) using the CSS coupling strategy to simulate the unsteady maneuvering flight. When compared with the results obtained using traditional lifting-line analyses, the coupled CFD-CSD wake coupling approach shows considerable improvement in the ability to capturing the dynamic stall events on the retreating side of the rotor disk. The overall mean lift time history is predicted reasonably. However, the magnitude of the dynamic stall events on the retreating side is underpredicted, and the third stall event on the advancing side is not captured. The results are consistent with those obtained using other solvers, as well as the wake-capturing analyses using the OVERTURNS-UMARC2 coupling.
This paper presents a study of three flight maneuvers using a rotorcraft aeroacoustics model: "po... more This paper presents a study of three flight maneuvers using a rotorcraft aeroacoustics model: "pop-up," "popdown," and an arrested descent. A time-accurate freevortex rotor wake model and a maneuvering rotor noise prediction code were used to compute the noise. All rotorcraft motions and rigid body blade motions were included in the respective models. The wake geometry and its development is described. It is shown that the magnitude and directivity of the noise is strongly dependent on the rotor wake characteristics when blade-vortex interactions occur. In the transient arrested descent maneuver, the wake geometry becomes extremely complicated, and a significant increase in both nonimpulsive and impulsive noise is predicted.
Abstract: A computational framework for coupled aeroelastic analysis of helicopter rotors was dev... more Abstract: A computational framework for coupled aeroelastic analysis of helicopter rotors was developed, tested and successfully validated as part of the HUSH program. The Python-based framework allows the combination of solvers of different disciplines for analysis of different rotorcraft problems in both serial and parallel computing environments. In addition, the framework standardized code interfaces such that multiple codes which have similar functionality can be substituted with ease thereby increasing the spectrum of verification ...
The effectiveness of a leading-edge slat in mitigating the adverse effects of dynamic stall on ro... more The effectiveness of a leading-edge slat in mitigating the adverse effects of dynamic stall on rotor blade aerodynamic and dynamic response was analyzed using a coupled CFD-CSD methodology. The capability of the CFD analysis to accurately predict the aerodynamics associated with a slatted airfoil was �rst validated against available 2-D wind-tunnel measurements of Lorber et al for steady and dynamic angle of attack variations. The results indicated that the slatted airfoil is able to achieve higher static lift coef�cients compared to the baseline airfoil by delaying the onset of boundary layer separation on the main airfoil section. The drop in the pitching moment coef�fcient is less severe in the presence of a slat. The slatted airfoil is also shown to perform better in unsteady conditions. The four-bladed UH-60A rotor geometry was then analyzed for a high- altitude, high-thrust �ight condition (designated counter 9017 in the UH-60A Airloads database) using the coupled CFD-CSD anal...
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Papers by Shreyas Ananthan