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    Quasi-static loads analysis of a 5-bladed rotor in maneuver using CFD/CSD coupling
    ( 2019) Hong, S. ; Jung, S. ; Kim, K. ; Park, S.H. ; Lee, D. ; Lee, J.
    The airloads and structural loads of Light Civil Helicopter (LCH) rotor in a pull-up maneuver are investigated using a coupled approach between the computational structural dynamics (CSD) and computational fluid dynamics (CFD) methods. The LCH rotor characterized by 5-bladed system with elastomeric bearing and inter-bladed damper is modeled in the structural dynamics analysis. The periodic rotor solution along with its converged CFD/CSD delta airloads for steady level flight (? = 0.287) is used to perform the transient maneuver analysis. The resulting vehicle attitude angles and velocity profiles are then prescribed for the quasi-static maneuver analysis of the rotor. The predicted section airloads, vortex trajectories, angle of attack (AOA)distributions, and structural moments at specified instants and spatial locations are compared between transient CSD-alone predictions and quasi-static CFD/CSD maneuver results. It is demonstrated that CFD/CSD coupled results indicate more pronounced dynamic stall peaks and stronger 5 /rev oscillations on structural moments than those by the CSD-alone approach.
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    A safety prompt method for helicopter formation flight
    ( 2019) Shanxiao ; Huang ; Yang ; Lu. ; Chao ; Zhou
    Aiming at the formation maintenance and comprehensive collision avoidance of the helicopter formation under "Leader-follower" mode, a safety prompt method is proposed. This method is based on the artificial potential field method to maintain formation and prevent collision of terrain and other formation members, which prompts helicopter to perform compound escape maneuver when it encounters obstacles and deviates from formation. After determining the research method, the safety threshold of formation maintenance and comprehensive collision avoidance during helicopter formation flying is discussed. Finally, the correctness of the method is verified by numerical simulation.
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    Interactional structural loads of the XV-15 rotor in airplane mode
    ( 2019) Lim, J.W. ; Tran, S.
    An investigation of the rotor/airframe interactions of the XV-15 tiltrotor aircraft in airplane mode is conducted using high fidelity CFD. To separate the rotor installation effects, an isolated rotor and a half-span full aircraft are simulated at the cruise speeds of 160 and 220 knots. The installed rotor displays a doublet aerodynamic loading near the 270o azimuth along with low-frequency mode harmonic airloads in the first half of the cycle. The doublet aerodynamic loading is due to the interactions with the wing and the low-frequency harmonic airloads are due to the rotor dynamics and longitudinal cyclic pitch control. The installed rotor thrust and power display significant 3/rev loading that is typical for a three-bladed rotor. More importantly, the resulting low-frequency mode harmonic airloads trigger vibrations on the rotor as a forcing function. The installed rotor displays significant installation effects on the 2 to 4/rev harmonics of the blade torsional, flap, and lead-lag moments at 220 knots.
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    Learning-based clustering for Flight Condition Recognition
    ( 2019) ?enipek, M. ; Kalkan, U.
    This paper presents flight condition recognition (FCR) algorithms for rotorcraft health and usage monitoring systems (HUMS), which are developed by using the clustering techniques of machine learning. Training and validation dataset are generated by using a generic nonlinear helicopter simulator and several flight data are obtained to train the algorithm. Gaussian Mixture Model (GMM), Neural Networks (NN) and Logistical Regression (LR) algorithms are implemented to perform FCR analyses. Validation and comparison studies are performed and results are compared in terms of accuracy, execution and training time. Finally, a detailed flight report about the flight is provided with percentages of performed flight conditions, which is used to provide feedback for health and usage monitoring systems to predict the life of the aircraft components.
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    Comprehensive rotorcraft aeroacoustics: investigation of surface pressure distribution methods for rotor noise
    ( 2019) ?enipek, M. ; Yücekayali, A. ; Özyörük, Y.
    Having full helicopter trim capability, comprehensive codes are indispensable for helicopter aeromechanics yet they operate over spanwise concentrated aerodynamic loads calculated at blade segment aerodynamic centers. In this study, an approach to generate distributed aerodynamic loads from comprehensive models, over real blade geometry for further aeroacoustic calculations of a helicopter rotor is proposed. Distribution of concentrated aerodynamic loads over upper and lower surface of the blade geometry with the help of an airfoil pressure database to prepare higher resolution data for acoustic solvers is studied. In order to assess the improvement, first, the concentrated aerodynamic loads are distributed over two-dimensional representative upper and lower surfaces then over three-dimensional blade geometry and acoustic signatures are compared with each other, HART-II wind tunnel test data and benchmark tool PSU-WOPWOP.