A Free-Wake Euler and Navier-Stokes CFD Method and its Application to Helicopter Rotors Including Dynamic Stall

Srinivasan, Ganapathi R.

doi:10.21236/ada278000

Cited by 12 publications

(5 citation statements)

References 16 publications

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“…The non-dimensional distance of the first layer of cells from the solid surface of the blade is of the order of y + = 1 for hover and forward flight conditions, which is sufficient for resolving the laminar part of the turbulent boundary layer using low-Re turbulence model of LEA k-ω. Three types of boundary conditions are applied in the numerical simulation: no-slip condition with zero heatflux (adiabatic) at the rotor blades, Froude [19] (hover case) and far-field conditions (forward flight case) at the edge of the background grids and a special chimera condition at the outer edge of the blade component grids which is necessary for the interpolation of the flow variables between meshes. For the flow control cases, a vortex generator component grid is added to the chimera setup.…”

mentioning

confidence: 99%

Application of a Passive Flow Control Device on Helicopter Rotor Blades

Tejero¹,

Doerffer²,

Szulc³

2016

J Am Helicopter Soc

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Application of an efficient flow control system on helicopter rotor blades may lead to improved aerodynamic performance. Recently, the own invention of a passive vortex generator (Rod Vortex Generator-RVG) has been analysed for channel and wing flows proving its capability to reduce flow separation. The application of this passive flow control device on helicopter rotor blades is described in the present paper. The basic flow mechanism is based on the intensification of exchange of momentum in the direction normal to the wall by a streamwise vortex. High momentum air is transferred to the low momentum region close to the surface and therefore the separation bubble is reduced. The present CFD investigation was carried out with the FLOWer code from DLR which solves the Favre-averaged Navier-Stokes equations using the chimera overlapping grids technique and LEA (Linear Explicit Algebraic Stress) k-ω turbulence model. The validation of the numerical setup for high-speed transonic hover conditions is based on a comparison with experimental data obtained by Caradonna and Tung (1981). For forward flight regime, the validation is based on a comparison with flight test data gathered by Cross and Watts for the AH-1G helicopter (1988). It has been proven that the application of the proposed flow control system reduces the size of the separation bubble increasing the aerodynamic performance in both states of flight. Nomenclature Symbols c blade chord (m) d rod diameter (m) h rod height (m) L spacing between vortex generators (m) M Mach number (-) M T tip Mach number (-) M ∞ forward flight Mach number (-) Re T tip Reynolds number (-) r rod radius (m) V ∞ forward flight velocity (km/h) C f skin friction coefficient (-) C P blade pressure coefficient (-) C Po rotor power coefficient (-) C Q rotor torque coefficient (-) C T rotor thrust coefficient (-) α rod skew angle (˚) β c backward disk tilt (˚) β s sideways disk tilt (˚) δ boundary layer thickness (m) µ rotor advance ratio (-) θ 0 blade collective angle (˚) θ c lateral cyclic coefficient (˚) θ s longitudinal cyclic coefficient (˚) ϴ rod pitch angle (˚) ψ blade azimuthal position (˚) Abbreviations C-T Caradonna and Tung FC Flow Control RVGs Rod Vortex Generators VGs Vortex Generators 40th European Rotorcraft Forum 2014, Proceedings of a meeting held 2

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confidence: 99%

Application of a Passive Flow Control Device on Helicopter Rotor Blades

Tejero¹,

Doerffer²,

Szulc³

2016

J Am Helicopter Soc

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“…The boundary conditions for the farfield boundaries employ a source-sink model. These conditions were prescribed at a distance of four rotor radii away from the rotor plane and for the outflow, a potential sink or Froude condition was used [39]. A quarter segment of the rotor and its surrounding field was created similar to that shown in Fig.…”

Section: Hover Resultsmentioning

confidence: 99%

Optimizing Rotor Blades with Approximate British Experimental Rotor Programme Tips

Johnson

Barakos

2014

Journal of Aircraft

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This work presents a framework for the optimization of certain aspects of a British Experimental Rotor Programme-like rotor blade in hover and forward flight so that maximum performance can be obtained from the blade. The proposed method employs a high-fidelity, efficient computational fluid dynamics technique that uses the harmonic balance method in conjunction with artificial neural networks as metamodels, and genetic algorithms for optimization. The approach has been previously demonstrated for the optimization of blade twist in hover and the optimization of rotor sections in forward flight, transonic aerofoils design, wing and rotor tip planforms. In this paper, a parameterization technique was devised for the British Experimental Rotor Programme-like rotor tip and its parameters were optimized for a forward flight case. A specific objective function was created using the initial computational fluid dynamics data and the metamodel was used for evaluating the objective function during the optimization using the genetic algorithms. The objective function was adapted to improve forward flight performance in terms of pitching moment and torque. The obtained results suggest optima in agreement with engineering intuition but provide precise information about the shape of the final lifting surface and its performance. The main computational cost was associated with the population of the genetic algorithms database necessary for the metamodel, especially because a full factorial method was used. The computational time of the optimization process itself, after the database has been obtained, is relatively insignificant. Therefore, the computational time was reduced with the use of the harmonic balance method as opposed to the time marching method. The novelty in this paper is twofold. Optimization methods so far have used simple aerodynamic models employing direct "calls" to the aerodynamic models within the optimization loops. Here, the optimization has been decoupled from the computational fluid dynamics data allowing the use of higher-fidelity computational fluid dynamics methods based on Navier-Stokes computational fluid dynamics. This allows a more realistic approach for more complex geometries such as the British Experimental Rotor Programme tip. In addition, the harmonic balance method has been used in the optimization process.

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“…The TURNS code models the vortex analytically as described in Refs. [22,23] and computes the MICROPHONE STAND surrounding flowfield to satisfy the conservation equations. The analytic vortex model simplifies the analysis since the vortex cannot diffuse from numerical dissipation in the CFD method.…”

Section: Results: Parallel Blade-vortex Interaction Noisementioning

confidence: 99%

New computational methods for the prediction and analysis of helicopter noise

Strawn

Oliker

Biswas

1996

Aeroacoustics Conference

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This paper describes several new methods to predict and analyze rotorcraft noise. These methods are: (1) a combined CFD and Kirchhoff scheme for far-field noise predictions, (2) parallel computer implementation of the Kirchhoff integrations, (3) audio and visual rendering of the computed acoustic predictions over large far-field regions, and (4) acoustic tracebacks to the Kirchhoff surface to pinpoint the sources of the rotor noise. The paper describes each method and presents sample results for three test cases. The first case consists of in-plane high-speed impulsive noise and the other two cases show idealized parallel and oblique blade-vortex interactions. The computed results show good agreement with available experimental data but convey much more information about the far-field noise propagation. When taken together, these new analysis methods exploit the power of new computer technologies and offer the potential to significantly improve our prediction and understanding of rotorcraft noise. (Author) ABSTRACTThis paper describes several new methods to predict and analyze rotorcraft noise. These methods are: 1) a combined computational fluid dynamics and Kirchhoff scheme for far-field noise predictions, 2) parallel computer implementation of the Kirchhoff integrations, 3) audio and visual rendering of the computed acoustic predictions over large far-field regions, and 4) acoustic tracebacks to the Kirchhoff surface to pinpoint the sources of the rotor noise. The paper describes each method and presents sample results for three test cases. The first case consists of in-plane high-speed impulsive noise and the other two cases show idealized parallel and oblique blade-vortex interactions. The computed results show good agreement with available experimental data but convey much more information about the far-field noise propagation. When taken together, these new analysis methods exploit the power of new computer technologies and offer the potential to significantly improve our prediction and understanding of rotorcraft noise.

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A Free-Wake Euler and Navier-Stokes CFD Method and its Application to Helicopter Rotors Including Dynamic Stall

Cited by 12 publications

References 16 publications

Application of a Passive Flow Control Device on Helicopter Rotor Blades

Application of a Passive Flow Control Device on Helicopter Rotor Blades

Optimizing Rotor Blades with Approximate British Experimental Rotor Programme Tips

New computational methods for the prediction and analysis of helicopter noise

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