Aerodynamic Performance of a Coaxial Hex-Rotor MAV in Hover

Micro aerial vehicles (MAVs) usually suffer from several challenges, not least of which are unsatisfactory hover efficiency and limited fly time. This paper discusses the aerodynamic characteristics of a novel Hex-rotor MAV with a coaxial rotor capable of providing higher thrust in a compact structure. To extend the endurance during hover, flow field analysis and aerodynamic performance optimization are conducted by both experiments and numerical simulations with different rotor spacing ratios (i = 0.56, 0.59, 0.63, 0.67, 0.71, 0.77, 0.83, 0.91). The measured parameters are thrust, power, and hover efficiency during the experiments. Retip ranged from 0.7 × 105 to 1.3 × 105 is also studied by Spalart–Allmaras simulations. The test results show that the MAV has the optimum aerodynamic performance at i = 0.56 with Retip = 0.85 × 105. Compared to the MAV with i = 0.98 for Retip = 0.85 × 105, thrust is increased by 5.18% with a reduced power of 3.8%, and hover efficiency is also improved by 12.14%. The simulated results indicate a weakness in inter-rotor interference with the increased rotor spacing. Additionally, the enlarged pressure difference, reduced turbulence, and weakened vortices are responsible for the aerodynamic improvement. This provides an alternative method for increasing the MAV fly time and offers inspiration for future structural design.

Choice of Interceptor Aerodynamic Lifting Surface Location based on Autopilot Design Considerations

Interceptors operate at wide range of operating conditions in terms of Mach number, altitude and angle of attack. The aerodynamic design caters for such wide operating envelope by appropriate sizing of lifting and control surfaces for meeting the normal acceleration capability requirements. The wide range of operating conditions leads to an inevitable spread in center of pressure location and hence spread in static stability. The performance of control design is a strong function of the aerodynamic static stability. The total operating envelope can be bifurcated into statically stable and unstable zones and the aerodynamic lifting surface location can be used as a control parameter to identify the neutral stability point. During the homing phase lesser static stability is desirable for good speed of response, hence the lifting surface location needs to be chosen based on the capability of control to handle instability. This paper analyses the limitations of autopilot design for the control of an unstable interceptor and brings out a method to identify the optimum aerodynamic lifting surface location for efficiently managing static margin while satisfying the control limitations and homing phase performance. This provides an input on the most appropriate lifting surface location to the aerodynamic designer during the initial CFD based aerodynamic characterisation stage itself, before commencing the rigorous wind tunnel based characterisation.

Review on Aerodynamic Drag Reduction of Vehicles

Due to higher price, limited supply and negative impacts on environment by fossil fuel, automobile industries have directed their concentrations in reducing the fuel consumption of vehicles in order to achieve the lower aerodynamic drag. As a consequence, numerous researches have been carried out throughout the world for not only getting the optimum aerodynamic design with lower drag penalty and but also other parameters that increases the fuel consumption. In this regard, relevant experimental and numerical outcomes on vehicle drag reduction considering various techniques such as active, passive and combined techniques in order to delay or suppress flow separation behind the vehicles have been considered in this review paper. Furthermore, the effects of drag reduction and their applicability on the vehicles are also illustrated in this paper. Therefore, it is conjectured that the drag reduction has been improved as much as 20%, 21.2%, and 30% by using the active, passive and combined control systems, respectively.

Optimum Aerodynamic Design of Centrifugal Compressor Impeller Using an Inverse Method Based on Meridional Viscous Flow Analysis

An optimum aerodynamic design method for centrifugal compressor impeller has been developed. The present optimum design method is using a genetic algorithm (GA) and a two-dimensional inverse blade design method based on a meridional viscous flow analysis. In the meridional viscous flow analysis, an axisymmetric viscous flow is numerically analyzed on a two-dimensional meridional grid to determine the flow distribution around the impeller. Full and splitter blade effects to the flow field are successfully evaluated in the meridional viscous flow analysis by a blade force modeling. In the inverse blade design procedure, blade loading distribution is given as the design variable. In the optimization procedure, the total pressure rise and adiabatic efficiency obtained from the meridional viscous flow analysis are employed as objective functions. Aerodynamic performance and three-dimensional flow fields in the Pareto-optimum design and conventional design cases have been investigated by three-dimensional Reynolds averaged Navier-Stokes (3D-RANS) and experimental analyses. The analyses results show performance improvements and suppressions of flow separations on the suction surfaces in the optimum design cases. Therefore, the present aerodynamic optimization using the inverse method based on the meridional viscous flow analysis is successfully achieved.

Study on aerodynamic optimal super/transonic turbine cascade and its geometry characteristics

The shock waves are important phenomena in transonic turbines, which cause lots of negative effects on the aerodynamic performance. Much of attention had been paid on reducing the strength of the shock waves via modifying turbine cascade geometry, and it is highly preferred to build experiences on the relationship between the cascade aerodynamic performance and the geometric parameters. The paper presents a numerical study on the aerodynamic optimal transonic turbine cascade and its geometry characteristics. Three typical Russia transonic turbine cascades with different design conditions are selected and optimized using adjoint method at three different back pressures, respectively. Thus, the best geometry parameters for optimum aerodynamic performance can be found. Then the key geometry parameters of optimized cascades are extracted and compared with the original ones. Results show that even the best designs by hands could be less efficient than ones by computer-aided optimizations. Some experiences on how to set the key geometry parameters for a best performance are obtained. The reduced shock profiling is applied to the thermal turbomachinery and machine dynamics transonic turbine by using the adjoint method. The performance of the thermal turbomachinery and machine dynamics transonic turbine was increased significantly.

Development of New High AN2 Last LP Stage Turbine and Exhaust Systems: A Cost Effective Solution for the 21st Century

A new high AN2 last LP stage turbine has been developed to provide leading performance for turbomachines in the 21st Century. It required a multi-disciplinary design approach involving aerodynamics, materials, mechanics (stress and vibration) and manufacturing technologies. The objective of the design was to achieve around 5% gain in last stage total-to-static efficiency, relative to the current competitive datum, for a very compact machine with few parts count ie reduced cost. It is shown how the optimum aerodynamic design was achieved for the stage. The paper presents details of the novel approaches used for the design including preliminary optimization, blading design and results from multistage 3D viscous predictions. The new stage has been tested in a Warm Air Turbine test rig at full scale engine representative conditions. The “loop was closed” by comparing the detailed test measurements with throughflow and 3D viscous analyses. This gives high confidence in the new approaches used. Additionally, the development of new compact high performance axial-radial and axial exhaust systems, which were designed to operate downstream of the new last LP stage, are described. To achieve the optimum performance, the last LP stage has to designed as a coupled system with the exhaust diffusers. The new LP technologies have already been scaled and cloned to a new engine design and sold by the Company.