A Computational Study of Outwash for a Helicopter Operating Near a Vertical Face with Comparison to Experimental Data

Polsky, Susan; Wilkinson, Colin

doi:10.2514/6.2009-5684

Cited by 14 publications

(9 citation statements)

References 7 publications

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“…In the past, several experimental investigations [2][3][4][5][6][7][8] have been carried out to study the influence of the obstacles on the flow field and the performance of rotors. The flow recirculation phenomena for rotors operating near the ground and obstacles were first studied by Timm through flow visualization [2].…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the effects of wake of a large upstream object to a nearby rotorcraft was also conducted at the Fluid Mechanics Laboratory (FML), NASA Ames Research Center, and focused on basic fluid mechanics of the aerodynamic interaction between a rotor and a wake [4]. Moreover, the flow field in the vicinity of a helicopter hovering near a hangar was studied at the National Research Council (NRC) Flight Research Laboratory (FRL) [5]. More recently, the effect of the confined area geometry on the aerodynamic performance of a hovering rotor was investigated [6].…”

Section: Introductionmentioning

confidence: 99%

“…To date, numerical investigations [3][4][5][9][10][11][12], ranging from simple blade element vortex methods to Navier-Stokes-based CFD, have been employed to study the aerodynamic interaction between rotorcraft wake and obstacles. The aim of the numerical simulation is to find the best method that one can use for simulating such flow.…”

Section: Introductionmentioning

confidence: 99%

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Simulation of the aerodynamic interaction between rotor and ground obstacle using vortex method

et al. 2018

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The mutual aerodynamic interaction between rotor wake and surrounding obstacles is complex, and generates high compensatory workload for pilots, degradation of the handling qualities, and performance, and unsteady force on the structure of the obstacles. The interaction also affects the minimum distance between rotorcrafts and obstacles to operate safely. A vortex-based approach is then employed to investigate the complex aerodynamic interaction between rotors and ground obstacle, and identify the distance where the interaction ends, and this is also the objective of the GARTEUR AG22 working group activities. In this approach, the aerodynamic loads of the rotor blades are described through a panel method, and the unsteady behaviour of the rotor wake is modelled using a vortex particle method. The effects of the ground plane and obstacle are accounted for via a viscous boundary model. The method is then applied to a "Large" and a "Wee" rotor near the ground and obstacle, and compared with the earlier experiments carried out at the University of Glasgow. The results show that predicted rotor induced inflow and flow field compare reasonably well with the experiments. Furthermore, at certain conditions, the tip vortices are pushed up and re-injected into the rotor wake due to the effect of the obstacle resulting in a recirculation. Moreover, contrary to without the obstacle case, peak and thickness of the radial outwash near the obstacle are smaller due to the barrier effect of the obstacle, and an upwash is observed. In addition, as the rotor closes to the obstacle, the rotor slipstreams impinge directly on the obstacle, and the upwash near the obstacle is faster, indicating a stronger interaction between the rotor wake and the obstacle. In addition, contrary to the case without the obstacle, the fluctuations of the rotor thrust, and rolling and pitching moments are obviously strengthened. When the distance between the rotor and the obstacle is larger than 3R, the effect of the obstacle is small. Keywords Rotor wake • Flow field • Ground obstacle • Vortex particle method • Viscous boundary model List of symbols b, f Size of the rectangular panel (m) h xi , h yi , h zi Size of the integration cuboid (m) G Free-space Green's function, non-dimensional n Outward unit normal vector of surface, non-dimensional p Local pressure (Pa) p ref Far-field reference pressure (Pa) r Position vector (m) S r Rotor blade surface (m 2) S rw Rotor wake surface (m 2) t Time (s) Tangential of the body boundary, non-dimensional u Fluid velocity (m/s) ∞ Free-stream velocity (m/s) slip Induced velocity due to vorticity (m/s) v r Velocity of a point on the rotor surface (m/s) ref Referenced velocity of the rotor (m/s) V Velocity magnitude (m/s) x j Position of particle, m j Vector-valued vorticity of particle (1/s) Bound vortex sheet (1/s) Kernel function, non-dimensional µ Doublet of rotor blades (m 4 /s) ν Kinematic viscosity (m 2 /s) ρ Density (kg/m 3)

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Simulation of the aerodynamic interaction between rotor and ground obstacle using vortex method

et al. 2018

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“…Flow visualisations and a blade element vortex model with corrections for contraction and skewness of the wake and ground effect clearly show the development of a flow recirculation region behind the building and an alteration of the rotor downwash distribution that suggest the existence of mutual influence between rotorcraft and ground obstacles. Polsky and Wilkinson [4] investigated a similar configuration using monotone integrated large eddy simulation (MILES) and accounting for the atmospheric boundary layer. A hovering rotor, modeled as AD, near a hangar has been studied, analysing the effect of mesh density, different turbulence models and different inflow wind conditions.…”

Section: Introductionmentioning

confidence: 99%

Numerical modelling of the aerodynamic interference between helicopter and ground obstacles

et al. 2017

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Helicopters are frequently operating in confined areas where the complex flow fields that develop in windy conditions may result in dangerous situations. Tools to analyse the interaction between rotorcraft wakes and ground obstacles are therefore essential. This work, carried out within the activity of the GARTEUR Action Group 22 on “Forces on Obstacles in Rotor Wake”, attempts to assess numerical models for this problem. In particular, a helicopter operating in hover above a building as well as in its wake, one main rotor diameter above the ground, has been analysed. Recent tests conducted at Politecnico di Milano provide a basis for comparison with unsteady simulations performed, with and without wind. The helicopter rotor has been modelled using steady and unsteady actuator disk methods, as well as with fully resolved blade simulations. The results identify the most efficient aerodynamic model that captures the wakes interaction, so that real-time coupled simulations can be made possible. Previous studies have already proved that the wake superposition technique cannot guarantee accurate results if the helicopter is close to the obstacle. The validity of that conclusion has been further investigated in this work to determine the minimum distance between helicopter and building at which minimal wake interference occurs

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“…2, and a summary account is given by Refs 3, 4 and 5. As seen from these studies (2)(3)(4)(5) , major strides have been made in generating the database of flow velocity points, primarily based on CFD approaches and, to a lesser degree, based on wind-tunnel and full-scale experiments. This database presents an unharnessed opportunity for generating a relatively complete set of statistics and developing interpretive models.…”

Section: Introductionmentioning

confidence: 99%

Rotorcraft downwash impact on ship airwake: statistics, modelling, and simulation

2016

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Helicopter downwash impact on ship airwake is addressed from a three-pronged approach: (1) Analysis of one-point statistics of autospectrum and two-point statistics of cross-spectrum and coherence from a Computational Fluid Dynamics database of flow velocities effected by helicopter downwash and shipboard airwake; (2) Development of a mathematical framework for extracting interpretive turbulence models in closed form from these autospectral statistics; and (3) Simulation through white-noise-driven filters for the extracted models. The framework begins with an earlier-exercised perturbation-type series expansion of the autocorrelation for all three velocity components, where the first term of the series has a form of the von Karman longitudinal or lateral correlation function. After transformation into equivalent series of autospectrum, the coefficients in the series are evaluated by satisfying theoretical constraints and fitting a curve on a set of selected autospectral data points generated from the database. The framework represents a sensible combination of series expansion, exploitation of a database, and theoretical constraints to provide a foothold on airwake-downwash phenomenon for engineering analysis. It ensures that the extracted model and the autospectral data points have the same time scale, mean square value, and asymptotic decay according to the Kolmogorov –5/3 Law. The framework's strengths and weaknesses, and its major advancement over the earlier series-expansion schemes are also addressed. Finally it is shown that downwash increases airwake energy (mean square value) by one order of magnitude, and almost all of this airwake-downwash energy is concentrated within the bandwidth (0.16 <f(Hz) < 1.6) that affects flight mechanics.

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A Computational Study of Outwash for a Helicopter Operating Near a Vertical Face with Comparison to Experimental Data

Cited by 14 publications

References 7 publications

Simulation of the aerodynamic interaction between rotor and ground obstacle using vortex method

Simulation of the aerodynamic interaction between rotor and ground obstacle using vortex method

Numerical modelling of the aerodynamic interference between helicopter and ground obstacles

Rotorcraft downwash impact on ship airwake: statistics, modelling, and simulation

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