Influence of Blade Geometric Parameters on Aeroelastic Response of a Helicopter Rotor System
01 Jul 2013-Journal of Aerospace Engineering (American Society of Civil Engineers)-Vol. 26, Iss: 3, pp 555-570
TL;DR: In this article, a low-cost computational aeroelastic model including the structural coupling from geometric parameters and nonlinearities associated with structural modeling and dynamic stall, applicable to steady, level forward flight, has been developed.
Abstract: Rotary wing aeroelasticity is a highly complex phenomenon involving coupling between flexible blade dynamics and unsteady aerodynamics including stall and unsteady wake effects. In this paper, a low-cost computational aeroelastic model including the structural coupling from geometric parameters and nonlinearities associated with structural modeling and dynamic stall, applicable to steady, level forward flight, has been developed. The differential equations of motion are solved in time domain in a sequential manner to obtain the response of all the blades in the rotor system, the dynamic inflow variables, and the sectional loads at every time step. A fourth-order Runge-Kutta integration scheme has been adopted for solving the differential equations. Iterations are carried out until convergence is achieved in blade response and helicopter trim. The effect of blade geometric parameters such as pretwist, hinge offset, and torque offset on aeroelastic response of a helicopter rotor system is investigated numerically. It is shown that the structural coupling from blade geometric parameters significantly influences the rotor blade response and loads.
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TL;DR: In this paper, four key design parameters of cycloidal rotors, namely the airfoil section, the number of blades, the chord-to-radius ratio, and the pitching axis location, are analyzed with an analytical model and a numerical approach.
Abstract: In this work, four key design parameters of cycloidal rotors, namely the airfoil section; the number of blades; the chord-to-radius ratio; and the pitching axis location, are addressed. The four parameters, which have a strong effect on the rotor aerodynamic efficiency are analyzed with an analytical model and a numerical approach. The numerical method is based on a finite-volume discretization of two-dimensional Unsteady Reynolds Averaged Navier-Stokes equations on a multiple sliding mesh, are proposed and validated against experimental data. A parametric analysis is then carried out considering a large-scale cyclogyro, suitable for payloads above 100 kg, in hovering conditions. Results demonstrate that the airfoil thickness significantly affects the rotor performance; such a result is partly in contrast with previous findings for small- and micro-scale configurations. Moreover, it will be shown that increasing the number of blades could result in a decrease of the rotor efficiency. The effect of chord-to-radius will demonstrate that values of around 0.5 result in higher efficiency. Finally it is found out that for these large systems, in contrast with micro-scale cyclogyros, the generated thrust increases as the pitching axis is located away from the leading edge, up to 35% of chord length. Further the shortcomings of using simplified analytical tools in the prediction of thrust and power in non-ideal flow conditions will be highlighted and discussed.
39 citations
Cites background or methods from "Influence of Blade Geometric Parame..."
...Computational tools have been widely used for analysing the influence of several fluid-dynamic effects on the aerodynamic behaviour of pitching aerofoils (Wang et al. 2012; Gharali and Johnson 2013), rotary wings (Laxman et al. 2013) and on the efficiency of cyclogyros (Tang et al. 2015)....
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...2012; Gharali and Johnson 2013), rotary wings (Laxman et al. 2013) and on the efficiency of cyclogyros (Tang et al....
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TL;DR: The influence of the blade geometric parameters on the structural dynamic characteristics, response and loads of a helicopter rotor under hover condition in a whirl tower was investigated in this article, where a general geometry was considered for the rotor blade.
Abstract: The influence of the blade geometric parameters on the structural dynamic characteristics, response and loads of a helicopter rotor under hover condition in a whirl tower was investigated. A general geometry was considered for the rotor blade which included configuration parameters like root offset, torque offset, pre-twist, pre-cone, pre-droop, pre-sweep, tip-sweep and tip-anhedral. The option of placing concentrated masses at any location on the blade was also included. Natural frequencies and the corresponding mode shapes of the rotating blade were obtained by solving the linear, undamped structural dynamics model in the finite element domain. For calculating the response and loads on the rotor, the complete aeroelastic equation was solved in modal space. Aerodynamic models used in the aeroelastic loads calculations were Peters-He dynamic wake theory for inflow and the modified ONERA dynamic stall theory for airloads calculations. From the study, the blade structural dynamic characteristics are found to be sensitive to variation in blade geometric parameters. Tip-sweep was found to have significant effects on root oscillatory moments. The moments at the tip junction with the straight portion of the blade were found to be substantially affected by tip-sweep and tip-anhedral.
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TL;DR: The viscous, three-dimensional flowfield of a lifting helicopter rotor in hover is calculated by using an upwind, implicit, finite-difference numerical method for solving the thin layer Navier-Stokes equations as discussed by the authors.
Abstract: The viscous, three-dimensional flowfield of a lifting helicopter rotor in hover is calculated by using an upwind, implicit, finite-difference numerical method for solving the thin layer Navier-Stokes equations. The induced effects of the wake, including the interaction of tip vortices with successive blades, are calculated as part off the overall flowfield solution without using any ad hoc wake models. Comparison of the numerical results for the subsonic and transonic conditions show good agreement with the experimental data and with the previously published Navier-Stokes calculations using a simple wake model. Some comparisons with Euler calculations are also presented, along with some discussions of the grid refinement studies.
208 citations
144 citations
TL;DR: A detailed review of rotary-wing dynamic and aeroelastic problems was provided by Loewy, where a wide range of dynamic problems was reviewed in considerable detail as mentioned in this paper.
Abstract: Concise Perspective and Previous Surveys W HEN reviewing research in rotary-wing aeroelasticity (RWA), it is important to mention a few historical facts The Wright brothers flew in 1903, and Sikorsky built and started flying the first operational helicopter, the R-4 or (VS-316), in 1942 The R-4 was a three-bladed helicopter with a rotor diameter of 116 m and was powered by a 185-hp engine Thus, there is an initial gap of approximately four decades between fixed-wing and rotary-wing technologies Therefore, it is not surprising that certain rotary-wing problems, particularly those pertaining to unsteady aerodynamics, are still not well understood The situation is further compounded by the complexity of the vehicle when compared to fixed-wing aircraft The field of RWA has been the most active area in aeroelasticity during the last three decades This vigorous research activity has generated a considerable number of survey papers as well as several books that have been published on this topic These review papers, when considered in chronological order, provide a historical perspective on this evolving field1−13 One of the first significant reviews of rotary-wing dynamic and aeroelastic problems was provided by Loewy,11 where a wide range of dynamic problems was reviewed in considerable detail A more limited survey emphasizing the role of unsteady aerodynamics and vibration problems in forward flight was presented by Dat2 Two comprehensive reviews of rotary-wing aeroelasticity were presented by Friedmann3,4 In Ref 3, a detailed chronological discussion of the flap-lag and coupled flap-lag-torsion problems in hover and forward flight was presented, emphasizing the inherently nonlinear nature of the hingeless-blade aeroelastic stability problem The nonlinearities considered were geometrical nonlinearities because of moderate blade deflections In Ref 4, the role of unsteady aerodynamics, including dynamic stall, was examined, together with the treatment of nonlinear aeroelastic problems in forward flight Finite element solutions to RWA problems were also considered, together with the treatment of coupled rotor-fuselage problems Another detailed survey by Ormiston12 discussed the aeroelasticity of hingeless and bearingless rotors, in hover, from an experimental and theoretical point of view
93 citations