• Title, Summary, Keyword: Airloads

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Validation of HART II Structural Dynamics Predictions Based on Prescribed Airloads

  • Sa, Jeong-H.;You, Young-H.;Park, Jae-S.;Park, Soo-H.;Jung, Sung-N.
    • International Journal of Aeronautical and Space Sciences
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    • v.13 no.3
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    • pp.349-360
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    • 2012
  • In this study, the accuracy of CSD (Comprehensive Structural Dynamics) analysis on the evaluation of blade aeroelastic responses and structural loads of HART(Higher harmonic Aeroacoustic Rotor Test) II baseline rotor is assessed using a comprehensive rotorcraft dynamics code, CAMRAD II, and a nonlinear flexible multi-body dynamics analysis code, DYMORE. Considering insufficient measurement data for HART II rotor, prescribed airloads computed by a three-dimensional compressible flow solver KFLOW are used to replace the lifting-line airloads and thereby enhance the prediction capability of the comprehensive analyses. The CSD results on blade elastic deflections using the prescribed airloads indicate more oscillatory behavior than those by lifting-line based approaches, but the wave pattern becomes improved by including artificial damping into the rotor system. It is demonstrated that the structural load predictions are improved significantly by the prescribed airloads approach against the measured data, as compared with an isolated CSD analysis.

Numerical Investigation of Aerodynamic Interference in Complete Helicopter Configurations

  • Lee, Hee-Dong;Yu, Dong-Ok;Kwon, Oh-Joon;Kang, Hee-Jung
    • International Journal of Aeronautical and Space Sciences
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    • v.12 no.2
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    • pp.190-199
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    • 2011
  • Unsteady flow simulations of complete helicopter configurations were conducted, and the flow fields and the aerodynamic interferences between the main rotor, fuselage, and tail rotor were investigated. For these simulations, a three-dimensional flow solver based on unstructured meshes was used, coupled with an overset mesh technique to handle relative motion among those components. To validate the flow solver, calculations were made for a UH-60A complete helicopter configuration at high-speed and low-speed forward flight conditions, and the unsteady airloads on the main rotor blade were compared to available flight test data and other calculated results. The results showed that the fuselage changed the rotor inflow distribution in the main rotor blade airloads. Such unsteady vibratory airloads were produced on the fuselage, which were nearly in-phase with the blade passage over the fuselage. The flow solver was then applied to the simulation of a generic complete helicopter configuration at various flight conditions, and the results were compared with those of the CAMRAD-II comprehensive analysis code. It was found that the main rotor blades strongly interact with a pair of disk-vortices at the outer edge of the rotor disk plane, which leads to high pulse airloads on the blade, and these airloads behave differently depending on the specific flight condition.

KFLOW Results of Airloads on HART-II Rotor Blades with Prescribed Blade Deformation

  • Sa, Jeong-Hwan;Kim, Jee-Woong;Park, Soo-Hyung;Park, Jae-Sang;Jung, Sung-Nam;Yu, Yung-Hoon
    • International Journal of Aeronautical and Space Sciences
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    • v.10 no.2
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    • pp.52-62
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    • 2009
  • A three-dimensional compressible Navier-Stokes solver, KFLOW, using overlapped grids has recently been developed to simulate unsteady flow phenomena over helicopter rotor blades. The blade-vortex interaction is predicted for a descending flight using measured blade deformation data. The effects of computational grid resolution and azimuth angle increments on airloads were examined, and computed airloads and vortex trajectories were compared with HART-II wind tunnel data. The current method predicts the BVI phenomena of blade airloads reasonably well. It is found from the present study that a peculiar distribution of vorticity of tip vortices in an approximate azimuth angle range of 90 to 180 degrees can be explained by physics of the shear-layer interaction as well as the dissipation of numerical schemes.

Helicopter BVI Noise Prediction Using Acoustic Analogy and High Resolution Airloads of Time Marching Free Wake Method (자유후류기법에 의한 고해상도 공기력과 음향상사법을 이용한 헬리콥터 로터 블레이드-와류 상호작용 소음 예측)

  • Chung, K.;Lee, D.J.;Hwang, C.
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.3
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    • pp.291-297
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    • 2006
  • The BVI(blade vortex interaction) noise Prediction has been one of the most challenging acoustic analyses in helicopter aeromechanical Phenomenon. It is well known high resolution airloads data with accurate tip vortex positions are necessary for the accurate prediction of this phenomenon. The truly unsteady time-marching free-wake method, which is able to capture the tip vortices instability in hover and axial flights, is expanded with the rotor flapping motion and trim routine to predict unsteady airloads in forward and descent flights. And Farassat formulation 1-A based on the FW-H equation is applied for the noise prediction considering the blade flapping motion. Main objective of this study is to validate the newly developed prediction code. To achieve the objective, the descent flight condition of AH-1 OLS(operational loads survey) configuration is analyzed using present code. The predicted sectional thrust distribution and sectional airloads time histories show the present scheme is able to capture well the unsteady airloads caused by a parallel BVI. Finally, the predicted noise data, observed in two different positions where are 3.44 times of rotor radius far from the hub center, are quite reasonable agreements with the experimental data compared to the other analysis results.

CFD/CSD COUPLED ANALYSIS FOR HART II ROTOR-FUSELAGE MODEL AND FUSELAGE EFFECT ANALYSIS (HART II 로터-동체 모델의 CFD/CSD 연계해석과 동체효과 분석)

  • Sa, J.H.;You, Y.H.;Park, J.S.;Park, S.H.;Jung, S.N.;Yu, Y.H.
    • 한국전산유체공학회:학술대회논문집
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    • pp.343-349
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    • 2011
  • A loosely coupling method is adopted to combine a computational fluid dynamics (CFD) solver and the comprehensive structural dynamics (CSD) code, CAMRAD II, in a systematic manner to correlate the airloads, vortex trajectories, blade motions, and structural loads of the HART I rotor in descending flight condition. A three-dimensional compressible Navier-Stokes solver, KFLOW, using chimera overlapped grids has been used to simulate unsteady flow phenomena over helicopter rotor blades. The number of grids used in the CFD computation is about 24 million for the isolated rotor and about 37.6 million for the rotor-fuselage configuration while keeping the background grid spacing identical as 10% blade chord length. The prediction of blade airloads is compared with the experimental data. The current method predicts reasonably well the BVI phenomena of blade airloads. The vortices generated from the fuselage have an influence on airloads in the 1st and 4th quadrants of rotor disk. It appeared that presence of the pylon cylinder resulted in complex turbulent flow field behind the hub center.

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Comprehensive Code Validation on Airloads and Aeroelastic Responses of the HART II Rotor

  • You, Young-Hyun;Park, Jae-Sang;Jung, Sung-Nam;Kim, Do-Hyung
    • International Journal of Aeronautical and Space Sciences
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    • v.11 no.2
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    • pp.145-153
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    • 2010
  • In this work, the comprehensive structural dynamics codes including DYMORE and CAMRAD II are used to validate the higher harmonic control aeroacoustic rotor test (HART) II data in descending flight condition. A total of 16 finite elements along with 17 aerodynamic panels are used for the CAMRAD II analysis; whereas, in the DYMORE analysis, 10 finite elements with 31 equally-spaced aerodynamic panels are utilized. To improve the prediction capability of the DYMORE analysis, the finite state dynamic inflow model is upgraded with a free vortex wake model comprised of near shed wake and trailed tip vortices. The predicted results on aerodynamic loads and blade motions are correlated with the HART II measurement data for the baseline, minimum noise and minimum vibration cases. It is found that an improvement of solution, especially for blade vortex interaction airloads, is achieved with the free wake method employed in the DYMORE analysis. Overall, fair to good correlation is achieved for the test cases considered in this study.

AERODYNAMIC AND NOISE CALCULATIONS OF HELICOPTER ROTOR BLADES USING LOOSE CFD-CSD COUPLING METHODOLOGY (CFD-CSD 연계 기법을 이용한 로터 블레이드 공력 및 소음 해석)

  • Kang, H.J.;Kim, D.H.;Wie, S.Y.
    • Journal of computational fluids engineering
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    • v.19 no.3
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    • pp.62-68
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    • 2014
  • The aerodynamic and noise calculations were performed through the CFD-CSD loose coupling methodology. In the loose coupling process, the trimmed rotor airloads were predicted by the in-house CFD code based on unstructured overset meshes, and the trim of the rotorcraft and the aeroelastic deformation of rotor blades were accounted with the CAMRAD II rotorcraft comprehensive code. The set of codes was used to analyze the HART-II baseline test condition. The effect of grid resolution and time step was examined and the loose coupling approach was found to be stable and convergent for the case. Comparison of the resulting sectional airloads, structural deformations, the noise carpets and the wake geometry with experimentally measured data was presented and showed the good agreement.

Performance and Airloads Analyses for a Rigid Coaxial Rotor of High-Speed Compound Unmanned Rotorcrafts (고속 비행 복합형 무인 회전익기의 강체 동축반전 로터의 성능 및 공력 하중 해석)

  • Kwon, Young-Min;Park, Jae-Sang
    • Journal of the Korea Institute of Military Science and Technology
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    • v.23 no.4
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    • pp.311-318
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    • 2020
  • This study investigates the performance and blade airloads for a rigid coaxial rotor of high-speed compound unmanned rotorcrafts. The present compound unmanned rotorcraft uses not only a rigid coaxial rotor, but also wings and propellers for high-speed flights. For the rigid coaxial rotor in this work, CAMRAD II, a rotorcraft comprehensive analysis code, is used to study the performance at a flight speed of up to 250 knots and blade section lift forces at 230 knots. As the flight speed increases, the rotor power decreases; however, the power of propellers increases to overcome the drag force of a rotorcraft in high-speed flight. The effective lift-to-drag ratio of a rotor has the maximum value of about 11.6 which is much higher than the value of the conventional helicopter. The blade section lift forces of the upper and lower rotors at 230 knots show the similar variation trends for one rotor revolution, and the impulses because of the aerodynamic interaction between both rotors are observed.

Toward a More Complete Analysis for Fluid-Structure Interaction in Helicopters

  • Kim, Kyung-Hwan;Shin, Sang-Joon;Lee, Jae-Won;Yee, Kwan-Jung;Oh, Se-Jong
    • International Journal of Aeronautical and Space Sciences
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    • v.7 no.2
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    • pp.110-120
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    • 2006
  • There have been developed many structural and fluid rotorcraft analysis models in rotorcraft community, and also lots of investigations have been conducted to combine these two models. These investigations turn out to be good at predicting the airloads precisely, but they have not taken the blade nonlinear deflection into account. For this reason, the present paper adopts a sophisticated structural model which can describe three-dimensional nonlinear deflection of the blade. And it is combined with two types of aerodynamic model. First one is generalized Greenberg type of finite-time aerodynamic model, which is originally established for a fixed wing, but later modified to be suitable for coupled flap-lag-torsional aeroelastic analysis of the rotor blade. Second aerodynamic model is based on the unsteady source-doublet panel method coupled with a free wake model. The advantages of the present method are capabilities to consider thickness of the blade and more precise wake effects. Transient responses of the airloads and structural deflections in time domain are mainly analyzed in this paper.