Exploring the detached-eddy simulation for main rotor flows

This paper applies the Detached-Eddy Simulation (DES) method to resolve a larger part of the flow spectrum around rotor blades in hover and forward flight. A comparison between DES and Unsteady Reynolds–Averaged Navier–Stokes simulation was carried out for the case of a forward flying rotor suggesting that DES has great potential for rotor applications

Numerical simulation of aeroacoustics of hovering helicopter rotor

The specifics of the problem of estimating the noise of a hovering rotor, allows for some simplification of the Ffowcs Williams-Hawkins (FW-H) equation. Most published works dedicated to helicopter tonal noise estimates use the far-field formulation. This paper estimates the aeroacoustic emissions of a helicopter rotor in hover, for observers placed at different distances using the FW-H equation, including near-field and far-field terms. The blade pressure distribution is obtained from numerical simulations with the RANS equations. To demonstrate this approach, the near- and far-field contributions are analyzed for the model-scale UH-1H main helicopter rotor. For the numerical simulations, the HMB solver of Glasgow University and the ANSYS Fluent13 commercial solver are used. As the rotor blade behaviour is characterized by a complex motion in the computer program it is assumed that the blade is seen in as a rotating rigid body. The most commonly used mathematical model of the FW-H equation corresponds to the classical impermeable formulation. In this case, the source surface corresponds to the blade surface. Then, the acoustic pressure (based on the FW-H 1A formulation) is modified with empirical adjustments, based on the radiation Mach number. This was applied for the near- or far-field thickness noise depending on the rotor-observer distance

Distribution of Acoustic Power Spectra for an Isolated Helicopter Fuselage

The broadband aerodynamic noise can be studied, assuming isotropic flow, turbulence and decay. Proudman’s approach allows practical calculations of noise based on CFD solutions of RANS or URANS equations at the stage of post processing and analysis of the solution. Another aspect is the broadband acoustic spectrum and the distribution of acoustic power over a range of frequencies. The acoustic energy spectrum distribution in isotropic turbulence is non monotonic and has a maximum at a certain value of Strouhal number. In the present work the value of acoustic power peak frequency is determined using a prescribed form of acoustic energy spectrum distribution presented in papers by S. Sarkar and M. Y. Hussaini and by G. M. Lilley. CFD modelling of the flow around isolated helicopter fuselage model was considered using the HMB CFD code and the RANS equations

Aerodynamic optimization of helicopter rear fuselage

An optimization process for the rear helicopter fuselage is presented using Genetic Algorithms and Kriging surrogate models. Shape parameterization is carried out with the super ellipse technique employed for the well-known ROBIN fuselage. The simulations were based on the RANS equations solved using the HMB CFD code. It is shown that a decrease of fuselage drag around 2.5% is possible without compromising the structure and the functionality of the design. Combined with an optimization of the helicopter skids, benefits of up to 4.6% were possible. The demonstrated method can be applied to fuselages of any shape during the initial design phase

Simulation of flow around oscillating rotor blade section with aeroelastic flap

Flows around rotor blade sections equipped with active flaps with a degree of freedom in the flap deflection angle are considered in this paper. Results for oscillating flaps are presented. The resultant flap motion was found to couple with the unsteady air loads for cases of blade section in oscillatory translation

CFD simulation of helicopter rotor flow based on unsteady actuator disk model

Actuator Disks (AD) can provide characterizations of rotor wakes while reducing computational expense associated with modeling the fully resolved blades. This work presents an unsteady actuator disk method based on surface circulation distribution combined with empirical data, blade element theory and rotor momentum theory. The nonuniform circulation distribution accounts for 3D blade load effects, and in particular, tip loses. Numerical simulations were conducted for the isolated pressure sensitive paint model rotor blade in hover and forward flight using the HMB3 CFD solver of Glasgow University. Validation of CFD results in comparison with published numerical data was performed in hover, for a range of blade pitch angles using fully turbulent flow and the k-ω SST model. In forward flight, the vortex structures predicted using the unsteady actuator disk model showed configurations similar to the ones obtained using fully resolved rotor blades. Despite the reduced grid cells number, the CFD results for AD models captured well the main vortical structures around the rotor disk in comparison to the fully resolved cases

Validation of actuator disc circulation distribution for unsteady virtual blades model

The actuator disc method is an engineering approach to reduce computer resources in Computational Fluid Dynamics (CFD) simulations of helicopter rotors or aeroplane propellers. Implementation of an actuator disc based on rotor circulation distribution allows for approximations to be made while reproducing the blade tip vortices. Radial circulation distributions can be formulated according to the nonuniform Heyson-Katzoff “typical load” in hover. In forward flight, the nonuniform disk models include “azimuthal” sin and cos terms to reproduce the blade cyclic motion. The azimuthal circulation distribution for a forward flight mode corresponds to trimmed conditions for the disk rolling and pitching moments. The amplitude of the cos harmonic is analysed and compared here with presented in references data and CFD simulations results

Helicopter Fuselage Optimisation

No abstract available

Helicopter Fuselage Optimisation

No abstract available

Estimates of hover aerodynamics performance of rotor model

Hover computations were undertaken for a helicopter model rotor using Computational Fluid Dynamics (CFD). The influence of CFD mesh construction peculiarities and mesh parameters on the results was considered. Aerodynamics performance of the rotor were obtained including the rotor polar, loads per unit length, and vortical flow below the rotor disk was also visualized