Rajneesh Singh

Direct calculation of three-dimensional indicial lift response using computational fluid dynamics

An unsteady Euler solver is modie ed to calculate the indicial response of a rectangular wing to a step change in the angle of attack. In this new approach the grid time metrics include the velocity caused by the impulsive change in angle of attack, but the mesh is not moved accordingly. This approach avoids numerical instabilities and decouples the step change in the angle of attack from a pitch rate. Numerical results are validated by comparison with analytical results for two-dimensional indicial responses. The application of the same method to rectangular wings reveals important characteristics of the three-dimensional indicial response. It is found that the direct calculation of the indicial response using computational e uid dynamics gives quite accurate results and provides a rich database, in the absence of experimental data, to validate the approximations to indicial response.

Simulation and Design of Automobile Sunroof Buffeting Noise Control

This paper presents the success story of an application of Computational Fluid Dynamics (CFD) analysis for automotive sunroof buffeting simulation and noise control design. Computational analyses of flow over an open sunroof of a car are performed to study the buffeting phenomenon and to determine the buffeting noise magnitude and frequency. Computations are performed for sunroofs with two types of buffeting noise control mechanisms. Numerical predictions are compared with the wind tunnel measurements. It is shown that CFD analysis has great potential for sunroof design and development

Generalized Moving Gust Response Using CFD with Application to Airfoil-Vorte x Interaction

An Euler solver is used to calculate the gust response of an airfoil entering a moving sharp-edged gust. Lift time histories are examined for various advance ratios of gust propagation for a Mach number of 0.5. The accuracy of the computed results is demonstrated by comparing with the available analytical solution. Important characteristics of the gust response and resulting flow features are explained. A general function is developed, using optimization, to parametrize the gust response in terms of the advance ratio of the gust. Finally, unsteady loads are computed for airfoil-vortex interactions using this general moving-gust function; the significance of the gust propagation effects is shown.

CFD Analysis of Flapping Wings in Ultra-Low Reynolds Number Regime

Computational simulations are conducted to investigate the fluid dynamics of flapping wings at ultra-low Reynolds numbers for micro-aerial vehicle applications. Rigid solid wing and ‘comb’-like of the same planform and the equal thicknesses are considered in the current study. Incompressible flow simulations are carried out to compute flowfield and aerodynamic forces on the wings for two types of wing kinematic motions. A parametric study of geometric and kinematic parameters is also conducted to compare the two wings. The aerodynamic forces for Solid wing and the Comb wing are found to be quite similar at lower Reynolds number however the detailed examination of the forces showed that the force generation mechanisms on the two wings are quite different. Analysis suggests that the Comb wings can provide a significant weight savings with a minimal loss in the aerodynamic performance for ultra-low Reynolds number applications.

Control and Performance of a Reconfigurable Multicopter

This paper presents a concept of a multicopter that can be reconfigured between a quadcopter, hexacopter, octocopter, and decacopter. The controls for each of the configurations are identified, and for the configurations with control redundancy, the power optimal controls are presented. A dynamic simulation model is implemented and used to compare the various configurations. The maximum useful weights of the octocopter, hexacopter, and quadcopter were 76.5%, 53.1%, and 29.7% that of the decacopter, respectively. Over a range of useful weights, the decacopter required the least power when the useful weight was greater than around 23% of its maximum, due to lower induced and profile power requirements of the lighter-loaded, slower-spinning rotors. At lower useful weights, smaller configurations required less power due to their lower empty weight. Increasing the number of rotors increased the maximum hover endurance, cruise endurance, and maximum range. Maximum moments and accelerations produced by each airc...

Shape Optimization of a Ducted Rotor System for Aerodynamic Performance

A parametric study is carried out to optimize the design of a ducted rotor system. Computational Fluid Dynamics simulations were conducted for several designs to generate system performance characteristics data to develop surrogate models. Verfication of the accuracy of the surrogate models in representing the system performance was conducted and thereafter the surrogate models were used to investigate the design space to determine the optimum design. The study showed that the surrogate model approach is able to predict the performance within 3% of the computed data.

Investigation of Non-linear Effects on Aerodynamics and Acoustics of Blade-Vortex Interactions

The unsteady aerodynamic loads and the resulting far-field acoustics of an isolated parallel blade-vortex interaction are calculated using both linear and nonlinear methods for both the aerodynamics and the acoustics, in order to show the importance of, or lack thereof, of nonlinear contributions from the noise source generation or propagation. The unsteady blade loading time histories for linear aerodynamics are calculated using the indicial method with generalized gust response; while an Euler method is used for the non-linear aerodynamics. For the acoustic propagation the WOPWOP+ code is used with the classical surface monopoles and dipoles for the linear acoustics and the addition of a quadrupole surface for the non-linear acoustics. The quadrupole surface integration is obtained by making a far-field in-plane approximation to the quadrupole volume integration. The linearized aerodynamics and linear acoustics produces reasonable predictions of the acoustic time signatures in the hotspots due to blade-vortex interactions, even for local Mach numbers at the interaction as large as 0.88. However, the unsteadiness in the quadrupole source terms induced by the vortex interaction results in significantly increased quadrupole time signatures in the plane of the rotor for such high local Mach numbers.

On the significance of transonic effects on aerodynamics and acoustics of blade-vortex interactions

An Euler code is used to model an isolated vortex interacting parallel with a rotor blade at transonic conditions in both forward flight and hover. A new field velocity approach is used to incorporate the effects of the vortex in the solution. Blade loading tune histories and instantaneous pressure contours are examined to observe and explain the features of such transonic parallel blade-vortex interactions. A qualitative study is made of the transonic effects on the 3-D blade vortex interaction. It is found that the strength and impulsiveness of the interaction for forward flight is greater than the interaction for the same rotor in hover at the same sectional Mach number. Furthermore, the investigation of disturbance pressure contours out past the tip of the rotor blade reveals some qualitative changes in the formation and initial propagation of blade-vortex interaction noise when strong transonic effects are present.