Rotor Hover Performance Research Articles

On genetic algorithm and artificial neural network combined optimization for a Mars rotorcraft blade

The Mars rotorcraft can help the Mars rover to optimize the driving route and explore more efficiently. However, the thin and cold Martian atmosphere can heavily increase the consumed power of the rotorcraft blades and reduce the generated thrust, leading to the reduction in power loading. The aerodynamic force generated by the Mars rotorcraft blade can be significantly influenced by the blade structure, which has several main structural characteristics and needs to be well designed. A multivariable optimization design method of blade structure is proposed based on neural network, genetic algorithm, and computational fluid dynamics simulations. Experiments conducted in the Martian atmosphere simulator indicate that the Mars rotorcraft blades with the hyperbolic chord length distribution and twist have higher power loading in the constant collective pitch angle. • A model was built to predict rotor hover performance at low-Reynolds-number. • Established an optimization model of the planform of the Mars rotorcraft blade. • The optimized blade consumes 29% less power than the conventional blade. • The optimization rusult were verified experimentally in Mars simulated environment.

Improving predictions of transitional and separated flows using RANS modeling

In this paper, new concepts are presented from the aspects of viscous modeling and numerical scheme in an attempt to improve the prediction of rotor hover performance and associated viscous flow physics under a RANS statistic modeling framework. An improved viscous modeling is proposed to address the overprediction of flow separations faced by RANS modeling, which modifies the linear eddy viscosity models based on a new separation correction method. This concept is seamlessly implemented into two popular eddy viscosity models: the Spalart-Allmaras one-equation model and Menter's shear stress transport two-equation model. A new high order unstructured grid WENO scheme is adopted to improve the prediction of mean flow resolutions as well as viscous flow structures around the hovering rotor. Numerical results show significant improvements achieved in the prediction of rotor hover performance as well as viscous flow phenomena including boundary layer transitions and flow separations.

Geometry shape selection of NACA airfoils for Mars rotorcraft

Mars rotorcraft, as an aerial auxiliary platform can assist Mars rover to complete exploration missions, is of great significance in the field of planetary exploration. The complex terrain on Mars limits the working range of the Mars rover, whereas a rotorcraft can acquire high detection speed and efficiency, even fixed-point sample using the ability of vertical takeoff and landing. Very little work has been done to analyze the Mars rotorcraft hovering process and there is also limited experimental data exist on the unique Mars flight conditions. A proper understanding of the hovering process is necessary to design a Mars rotorcraft and verify whether it is appropriate or not. In this work, a modified BEMT-CFD model is developed to analyze inflow distribution in the wingspan direction and to predict the aerodynamic performance of the rotor system. Based on the developed model, a suitable airfoil is selected and the operational parameters are investigated to design a suitable rotor configuration for the Mars rotorcraft. Hover experiments demonstrate that the modified model can effectively predict the rotor hover performance. Using the suitable blade pitch angle and rotational speed, the rotor can generate enough thrust to support a 500 g rotorcraft to fly in the simulated Mars environment.

Assessment of S-76 rotor hover performance in ground effect using an unstructured mixed mesh method

In the present study, the aerodynamic performance of an S-76 rotor in hover was numerically investigated by using an unstructured mixed mesh flow solver. The study was made for the rotor for both OGE (out-of-ground-effect) and IGE (in-ground-effect) conditions, and the results are compared against each other. In the present mixed mesh methodology, body-fitted prismatic/tetrahedral mesh was adopted in the near-body flow domain to treat complex geometries easily and to capture the viscous layer on the solid surface more accurately, while in the off-body region away from the blades Cartesian mesh was used. To better resolve the flow characteristics and to prevent excessive numerical dissipation, a high-order accurate weighted essentially non-oscillatory (WENO) scheme was employed in the off-body flow region. An overset mesh topology was adopted to handle blade rotation and to exchange the flow variables between the two different mesh regions. The calculations were made for three different blade configurations, having swept-tapered, rectangular, and swept-tapered-anhedral tip shapes, and the results are compared with experimental rotor performance data in terms of thrust, torque and figure of merit. The predictions were obtained for a collective pitch angle sweep from 5 to 10 degrees at a tip Mach number of 0.60 for both with and without ground effects. The detailed flow characteristics, such as vorticity contours and tip-vortex trajectory, were also investigated.

Role of Blade Flexibility on Cycloidal Rotor Hover Performance

In this paper, the aeromechanics of a cycloidal rotor (or cyclorotor) is investigated to understand the effect of blade flexibility on the performance of the rotor in hover. Toward this, experiments are conducted on cyclorotors using moderately and highly flexible blades. These studies show that, with increasing blade flexibility, the rotor thrust decreases; whereas the power consumption increases, leading to a significant drop in power loading (thrust/power). To investigate these phenomena, a coupled aeroelastic model of cyclorotor is developed by coupling an unsteady aerodynamics model with a beam-based structural model and is systematically validated with experimental results. The aerodynamic model contains rigorous modeling of various physics behind the operation of the cyclorotor, such as the nonlinear dynamic virtual camber, the effect of near and shed wakes, and the leading-edge vortex. In comparison with a second-order nonlinear structural model, inclusion of a geometrically exact structural model proves to be essential in accurate prediction of rotor deflections and performance. Based on a systematic analysis performed using the validated model, it is observed that the large torsional deflections of the blades are a key reason for the drop in thrust. The torsional deflections are mainly produced by centrifugal force and nonlinear moments due to bending curvatures.

Accurate Predictions of Rotor Hover Performance at Low and High Disc Loadings

This paper presents evidence on the ability of modern computational fluid dynamics methods to accurately predict hover performance of rotors with modest computer resources. The paper uses two well-studied blades, the S-76 main rotor blade and the XV-15 tiltrotor blade. The results are compared with experiments and show that the performance is well predicted. In addition, the employed computational fluid dynamics method was able to capture the effects of the tip Mach number, tip shape, blade aeroelasticity, and flow transition on the performance of the blade as well as on the wake structure and the rotor acoustics.

Effect of Rotor Geometry and Blade Kinematics on Cycloidal Rotor Hover Performance

This paper describes the systematic performance measurements conducted to understand the role of rotor geometry and blade pitching kinematics on the performance of a microscale cycloidal rotor. Key geometric parameters that were investigated include rotor radius, blade span, chord, and blade planform. Because of the flow curvature effects, the cycloidal-rotor performance was a strong function of the chord/radius ratio. The optimum chord/radius ratios were extremely high, around 0.5–0.8, depending on the blade pitching amplitude. Cycloidal rotors with shorter blade spans had higher power loading (thrust/power), especially at lower pitching amplitudes. Increasing the solidity of the rotor by increasing the blade chord, while keeping the number of blades constant, produced large improvements in power loading. Blade planform shape did not have a significant impact, even though trapezoidal blades with a moderate taper ratio were slightly better than rectangular blades. On the blade kinematics side, higher blade pitching amplitudes were found to improve the power loading of the cycloidal rotor. Asymmetric pitching with a higher pitch angle at the top than at the bottom produced better power loading. The chordwise optimum pitching axis location was observed to be around 25–35% of the blade chord. The power loading of the optimized cycloidal rotor was higher than that of a conventional microrotor.

Assessment of Rotor Hover Performance Using a Node-based Flow Solver

A three-dimensional viscous flow solver has been developed for the prediction of the aerodynamic performance of hovering helicopter rotor blades using unstructured hybrid meshes. The flow solver utilized a vertex-centered finite-volume scheme that is based on the Roe's flux-difference splitting with an implicit Jacobi/Gauss-Seidel time integration. The eddy viscosity are estimated by the Spalart-Allmaras one-equation turbulence model. Calculations were performed at three operating conditions with varying tip Mach number and collective pitch setting for the Caradonna-Tung rotor in hover. Additional computations are made for the UH-60A rotor in hover. Reasonable agreements were obtained between the present results and the experiment in both blade loading and overall rotor performance. It was demonstrated that the present vertex-centered flow solver is an efficient and accurate tool for the assessment of rotor performance in hover.