CFD Analysis of Helicopter Wakes in Ground Effect

The paper presents CFD results for the wake of a helicopter flying a low altitude at different advance ratios. The wakes are assessed in terms of topology and velocity magnitudes. The structure of the wake near ground changes rapidly with the advance ratio and its decay appears to be faster than what is suggested by theoretical analyses. The results show clear the potential of modern CFD for use in helicopter safety and highlights the need for detailed surveys of helicopter wakes using full-scale physical experiments

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

CFD and aeroelastic analysis of the MEXICO wind turbine

This paper presents an aerodynamic and aeroelastic analysis of the MEXICO wind turbine, using the compressible HMB solver of Liverpool. The aeroelasticity of the blade, as well as the effect of a low-Mach scheme were studied for the zero-yaw 15m/s wind case and steady- state computations. The wake developed behind the rotor was also extracted and compared with the experimental data, using the compressible solver and a low-Mach scheme. It was found that the loads were not sensitive to the Mach number effects, although the low-Mach scheme improved the wake predictions. The sensitivity of the results to the blade structural properties was also highlighted

Flight simulation testing of a turbulence model based on a Synthetic Eddy Method

This paper presents initial analysis of an ongoing series of flight simulation trials of a new turbulence model based on a synthetic eddy method (SEM). The model is based on the generation of a random distribution of turbulence generating Eddies within a control model surrounding the aircraft. Eddies are displaced by the flow and regenerated at the inflow as they leave the simulation domain. The model allows adjustment of turbulence intensity by adjusting the value of Reynolds stress tensor and of frequency spectra through adjustment of eddy sizes, allowing for a more realistic representation of broadband turbulence. Compared to other random turbulence models, preserving the location of the Eddies in the control volume ensures automatically that turbulence across different aircraft locations is automatically correlated. Piloted flight simulation tests show that both, levels of turbulence intensity and frequency of the induced turbulence have a strong effect on workload and task performance. Increases in turbulence intensity result in a direct increase in pilot workload and reduced task performance. However changes in frequency of turbulence present a more complex picture dependent on flight condition and aircraft response

Assessment of Implicit Implementation of the AUSM+ Method and the SST Model for Viscous High Speed Flow

No abstract available

Shock interactions in continuum and rarefied conditions employing a novel gas-kinetic scheme

Shock interactions can have a significant impact on heating rates and aerodynamic performance of hypersonic vehicles. The study presents different shock interactions in partially rarefied hypersonic flows predicted employing a recently developed gas-kinetic scheme for diatomic gases with rotational degrees of freedom. The new gas-kinetic schemes will be presented along with shock/wave boundary interactions as well as Edney Type IV shock–shock interactions. Various levels of rarefaction have been considered to highlight the effect of thermal relaxation between the translational and rotational modes. In addition, for the Edney test case, the imposed wall temperature on the shock-generating wedge and the cylinder surface has been varied, to evaluate the importance of the boundary layer thickness in the interaction region

CFD Analysis of Rotor-Fuselage Aerodynamics based on a Sliding Mesh Algorithm

Rotor-fuselage interaction is central to the design and performance analysis of helicopters. However, regardless of its significance this problem is not well-studied and few CFD works have so far been published. In this paper, a method is put forward to allow CFD computations of rotor-fuselage problems using a sliding mesh to interface the rotor and fuselage regions. A sliding plane forms a boundary between a CFD mesh around the fuselage and a rotor-fixed CFD mesh which has to be rotated to account for the motion of the rotor blades. CFD meshes adjacent to a sliding plane do not necessarily have matching nodes or even the same number of cell-faces. This poses a problem of interpolation between CFD meshes and, in addition, the employed algorithms should have small CPU overhead. The properties of this method are assessed and validation results are presented for several flow case

Creating a Database of Helicopter Main Rotor Acoustics for Validation of CFD Methods

The work presents recent experiments at the Kazan National Technical University (KNRTU-KAI), related to helicopter acoustics. The objective is to provide a database of near-field experimental data suitable for CFD validation. The obtained set of data corresponds to a Mach-scaled rotor of known planform. An advantage of the current dataset is that direct near-field acoustic data is made available and this allows easy and direct comparisons with CFD predictions, without the need to use far-field aeroacoustic methods

Helicopter Fuselage Drag ─ Combined Computational Fluid Dynamics and Experimental Studies

In this paper, wind tunnel experiments are combined with Computational Fluid Dynamics (CFD) aiming to analyze the aerodynamics of realistic fuselage con¦gurations. A development model of the ANSAT aircraft and an early model of the AKTAI light helicopter were employed. Both models were tested at the subsonic wind tunnel of KNRTU-KAI for a range of Reynolds numbers and pitch and yaw angles. The force balance measurements were complemented by particle image velocimetry (PIV) investigations for the cases where the experimental force measurements showed substantial unsteadiness. The CFD results were found to be in fair agreement with the test data and revealed some §ow separation at the rear of the fuselages. Once con¦dence on the CFD method was established, further modi¦cations were introduced to the ANSAT-like fuselage model to demonstrate drag reduction via small shape changes

Calibration of the 7—equation transition model for high Reynolds flows at low mach

The numerical simulation of flows over large-scale wind turbine blades without considering the transition from laminar to fully turbulent flow may result in incorrect estimates of the blade loads and performance. Thanks to its relative simplicity and promising results, the Local-Correlation based Transition Modelling concept represents a valid way to include transitional effects into practical CFD simulations. However, the model involves coefficients that need tuning. In this paper, the γ—equation transition model is assessed and calibrated, for a wide range of Reynolds numbers at low Mach, as needed for wind turbine applications. An aerofoil is used to evaluate the original model and calibrate it; while a large scale wind turbine blade is employed to show that the calibrated model can lead to reliable solutions for complex three-dimensional flows. The calibrated model shows promising results for both two-dimensional and three-dimensional flows, even if cross-flow instabilities are neglected