A vortex embedding method for free wake analysis of helicopter rotor (original) (raw)

Influence of Helicopter Rotor Wake Modeling on Blade Airload Predictions

… of Engineering (IJE), 2010

In the present paper a computational investigation is made about the efficiency of recently developed mathematical models for specific aerodynamic phenomena of the complicated helicopter rotor flowfield. A developed computational procedure is used, based on a Lagrangian type, Vortex Element Method. The free vortical wake geometry and rotor airloads are computed. The efficiency of special models concerning vortex core structure, vorticity diffusion and vortex straining regarding rotor airloads prediction is tested. Investigations have also been performed in order to assess a realistic value for empirical factors included in vorticity diffusion models. The benefit of using multiple vortex line to simulate trailing wake vorticity behind blade span instead of isolated lines or vortex sheets, despite their computational cost, is demonstrated with the developed wake relaxation method. The computational results are compared with experimental data from wind tunnel tests, performed during joined European research programs.

Analysis of rotor wake aerodynamics during maneuvering flight using a free-vortex wake methodology

2006

The problem of helicopter rotor wake aerodynamics during maneuvering flight conditions was analyzed using a time-accurate, free-vortex wake methodology. The free-vortex method consists of a Lagrangian representation of the rotor flow field using vortex elements, where the evolution of the flow field is simulated by tracking the free motion of these vortex elements and calculating their induced velocity field. Traditionally, free-vortex methods are inviscid, incompressible models, but in the present approach the viscous effects are incorporated using a viscous splitting method where the viscous and inviscid terms are modeled as successive sub-processes. The rotor aerodynamics and rigid blade flapping dynamics are closely coupled with the wake model and solved for in a consistent manner using the same numerical scheme.

Lifting surface method for prediction of rotor vortex wake

Ce travail présente un modèle hybride pour étudier le sillage à l'aval des rotors d'hélicoptères et d'éoliennes. L'approche est basée sur un calcul CFD où les pales sont remplacées par des surfaces de discontinuité de pression. Cette modélisation allège le maillage autour du rotor ce qui permet d'améliorer la finesse autour des tourbillons. Le modèle est validé à l'aide des mesures PIV et révèle un intérêt pour les études d'interaction et du bruit aérodynamique.

Estimation of the circulation distribution on a rotor blade from detailed near wake velocities

Wind Energy, 2004

The circulation distribution over a blade of a wind turbine model is estimated by use of a vortex model, which is matched with measured wake properties. With near wake velocities and the Biot-Savart law an optimization scheme is constructed to estimate the circulation distribution over the blade using a polynomial function series to approximate the circulation distribution.The velocities resulting from the calculated distribution are compared with the measured data, and deviations are discussed and explained. The vortex model offers insight into how the measured velocities can be separated into induced velocities of the different parts of the vortex system, such as the influence of the tip vortex. The sensitivity of the vortex model to its most uncertain parameters is tested. Finally the circulation distribution obtained with the vortex model is compared with the circulation distribution obtained through application of a blade element momentum (BEM) code. The BEM results show an underestimation of the circulation near the root and an overestimation of the circulation near the tip with respect to the vortex model results.

Rotorcraft comprehensive code assessment for blade–vortex interaction conditions

Aerospace Science and Technology, 2018

The scope of this paper is the presentation of the computational methodologies applied in the comprehensive code for rotorcraft developed in the last years at Roma Tre University, along with the assessment of its prediction capabilities focused on flight conditions characterized by strong blade-vortex interactions. Boundary element method approaches are applied for both potential aerodynamics and aeroacoustics solutions, whereas a harmonic-balance/modal approach is used to integrate the rotor aeroelastic equations. The validation campaign of the comprehensive code has been carried out against the wellknown HART II database, which is the outcome of a joint multinational effort aimed at performing wind tunnel measurements of loads, blade deflection, wake shape and noise concerning a four-bladed model rotor in low-speed descent flight. Comparisons with numerical simulations available in the literature for the same test cases are also presented. It is shown that, with limited computational cost, the results provided by the Roma Tre aero-acousto-elastic solver are in good agreement with the experimental data, with a level of accuracy that is in line with the state-of-the-art predictions. The influence of the vortex core modeling on aerodynamic predictions and the influence of the inclusion of the fuselage shielding effect on aeroacoustic predictions are discussed.

Development of Free Vortex Wake Method for Aerodynamic Loads on Rotor Blades

Among clean energy sources that are renewable, wind is regarded as the least destructive to the environment. According to data provided by the Renewables Global Status Report in 2013, wind capacity increased globally by 19% per year, the increase being 45 GW. That is, it reached 283 GW to a record high despite the uncertainty in the policy in the key markets. By the exponential growth of wind turbines all around the world, and its general acceptance among people, the demand and its worthwhileness makes it apt for research, especially to enhance its performance. The aerodynamics of a wind turbine is governed by the flow around the rotor, where the prediction of air loads on rotor blades in different operational conditions and its relation to rotor structural dynamics is crucial for design purposes. One of the most important challenges in wind turbine aerodynamics is therefore to accurately predict the forces on the blade, where the blade and wake are modeled by different approaches such as the Blade Element Momentum (BEM) theory, the vortex method and Computational Fluid Dynamics (CFD). A free vortex wake method, based on the potential, inviscid and irrotational flow, is developed to study the aerodynamic loads. The results are compared with the BEM [1] method, the GENUVP [2] code and CFD [3] (see also the acknowledgments).

Computation of helicopter rotor wake geometry and its influence on rotor harmonic airloads

1975

Efficient techniques are developed for the computation of helicopter rotor tip vortex geometry and helicopter rotor harmonic airloads. These techniques are designed to minimize the computational expense by the use of simplified wake models together with other devices which reduce the amount of integration over the wake of the Biot Savart relation for induced velocity. These techniques are designed for use in steady-state flight at advance ratios below 0.3; however, they could be readily extended to higher advance ratios and to transient flight conditions.

Rotor Wake Computing With Lifting Lines and Vorticity Confinement

27th AIAA Applied Aerodynamics Conference, 2009

This paper describes a new method to compute rotor wakes. An incompressible flow solver, SAGE, with Vorticity Confinement (VC) is used for the rapid, accurate prediction of rotorcraft flow fields. A preliminary validation for SAGE has been done recently for computing rotor flows in hover and in forward flight. The computations of flow over an entire helicopter configuration, including main rotor and tail rotor, are performed in a uniform Cartesian grid. The rotor blades are represented by very efficient lifting lines using a simple momentum source representation together with VC. The airloads of the rotor blades can be prescribed or calculated from a more complex code with which SAGE is coupled, such as TURNS, or by a simple analytic model.

Rotor wake vortex definition–evaluation

An evaluation is made of extensive three-component (3-C) particle image velocimetry (PIV) measurements within the wake across a rotor disk plane. The model is a 40 percent scale BO-105 helicopter main rotor in forward flight simulation. This study is part of the HART II test program conducted in the German-Dutch Wind Tunnel (DNW). Included are wake vortex field measurements over the advancing and retreating sides of the rotor operating at a typical descent landing condition important for impulsive blade-vortex interaction (BVI) noise. Also included are advancing side results for rotor angle variations from climb to steep descent. Using detailed PIV vector maps of the vortex fields, methods of extracting key vortex parameters are examined and a new method was developed and evaluated. An objective processing method, involving a centerof-vorticity criterion and a vorticity "disk" integration, was used to determine vortex core size, strength, core velocity distribution characteristics, and unsteadiness. These parameters are mapped over the rotor disk and offer unique physical insight for these parameters of importance for rotor noise and vibration prediction.

Computation of rotor aerodynamic loads in forward flight using a full-span free wake analysis

1990

The development of an advanced computational analysis of unsteady aerodynamic loads on isolated helicopter rotors in forward flight is described. The primary technical focus of the development was the implementation of a freely distorting filamentary wake model composed of curved vortex elements laid out along contours of constant vortex sheet strength in the wake. This model captures the wake generated by the full span of each rotor blade and makes possible a unified treatment of the shed and trailed vorticity in the wake. This wake model was coupled to a modal analysis of the rotor blade dynamics and a vortex lattice treatment of the aerodynamic loads to produce a comprehensive model for rotor performance and air loads in forward flight dubbed RotorCRAFT (Computation of Rotor Aerodynamics in Forward Flight). The technical background on the major components of this analysis are discussed and the correlation of predictions of performance, trim, and unsteady air loads with experiment...