The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Jaewoo Lee - One of the best experts on this subject based on the ideXlab platform.

  • aerodynamic design optimization of helicopter rotor blades including airfoil shape for forward Flight
    Aerospace Science and Technology, 2015
    Co-Authors: Jaewoo Lee
    Abstract:

    Abstract This study proposes a process to obtain an optimal helicopter rotor blade shape including both planform and airfoil shape for helicopter aerodynamic performance in forward Flight. An advanced geometry representation algorithm which uses the Class Function/Shape Function Transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape was considered in terms of design variables. The optimization process was constructed by integrating several programs developed by the author. Airfoil characteristics are automatically generated by an analysis tool where lift, drag, and moment coefficients of airfoil are predicted for subsonic to transonic flow and a wide range of attack angles. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward Flight, aerodynamic requirements (lift, drag and moment coefficients) for critical flow Condition occurring on rotor blades. The trim Condition must be attainable in any Flight Condition. Objective function is chosen as a combination expression of non-dimensional required power in hover and forward Flight.

  • aerodynamic design optimization of helicopter rotor blades including airfoil shape for hover performance
    Chinese Journal of Aeronautics, 2013
    Co-Authors: Jaewoo Lee, Jung Il Shu
    Abstract:

    Abstract This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover Flight. A new geometry representation algorithm which uses the class function/shape function transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward Flight. The trim Condition must be attainable. This paper considers rotor blade configuration for the hover Flight Condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.

Shouhei Yanai - One of the best experts on this subject based on the ideXlab platform.

  • thermochemical process of nonequilibrium plasma flows in a mars entry Flight Condition
    13-TH NATIONAL CONGRESS ON THEORETICAL AND APPLIED MECHANICS, 2017
    Co-Authors: Gouji Yamada, Shouhei Yanai
    Abstract:

    Experimental and numerical studies are conducted to investigate characteristics of shock-induced plasma flows around a space vehicles entering into the Mars atmosphere. In this study, a shock tube is used to simulate a shock wave generated around a space vehicle in a Mars entry Flight Condition. Spectroscopic measurements of the plasma flows are conducted behind a shock wave generated in the shock tube. Measured spectra show the chemical composition of plasma flows and temporal evolution of chemical reaction processes. It is found that emissions of CN and C2 molecules are dominant in the measured spectra. The rotational and vibrational temperetures are derived from the measured spectra by a spectrum fitting technique and compared with the numerical ones obtained from the computational fluid dynamics (CFD) simulation. It is found that the measured rotational and vibrational temperatures are almost same immediately behind a shock wave, showing the disagreement with the calculated ones. The present result has indicated that the modification of the physical model used in the simulation is required by further investigations.

Cheng Gong - One of the best experts on this subject based on the ideXlab platform.

  • shape optimization and sensitivity analysis of a morphing wing aircraft
    International Journal of Aeronautical and Space Sciences, 2019
    Co-Authors: Cheng Gong
    Abstract:

    Morphing-wing concepts have received growing interests in the recent years for enhancing the multi-mission performance of unmanned aerial vehicle. However, to obtain a feasible morphing strategy, the optimization design studies are required. In this paper, an aerodynamic optimization study for a morphing-wing aircraft with variable sweep, span, and chord length was conducted to obtain the optimum configurations at subsonic, transonic and supersonic Conditions. The optimization objective is to obtain maximum lift-to-drag ratios subject to lift coefficients and static stability constraints at each Flight Condition. A genetic algorithm in conjunction with surrogate models was employed to search optimum solutions in the entire design space. The aerodynamic forces are calculated by an Euler-based solver and friction drag estimation code. The optimum configuration corresponding to any Flight Condition can be determined through the optimization. A global sensitivity analysis based on the surrogate model was also carried out, hence the contribution of each design variable to the optimization objective can be analyzed. The results indicated that the optimum wing at subsonic speeds have a lower sweep angle and high aspect ratio, and the wing sweep has a primary contribution to lift-to-drag ratios, and the span is secondary; at transonic Conditions, the medium-sweep wing is the optimum, and the contribution of the span is far more than other variables; at supersonic Conditions, the optimum configuration becomes a high-sweep cropped delta wing, and the span has a dominant contribution, and the sweep is secondary.

  • spark ignition process in a scramjet combustor fueled by hydrogen and equipped with multi cavities at mach 4 Flight Condition
    Experimental Thermal and Fluid Science, 2012
    Co-Authors: Cheng Gong, Shun Ping Zhang, Jian Han Liang, Z G Wang
    Abstract:

    Abstract The spark ignition process in the scramjet combustor fueled by hydrogen equipped with multi-cavities at Mach 4 Flight Condition was observed by high speed photography and Schlieren system, at the inflow Conditions of Ma  = 1.92 with stagnation state T 0  = 846 K, P 0  = 0.7 MPa. The spark kernel, the flame spreading process and shock structures in the combustor with different ignition and injection setups were well captured. The experiments revealed that flame kernel occurs near the igniter, and grows to form flame in the cavity. The initial flame spreads along the cavity shear layer and ignites the fuel distributed downstream very quickly. Along with the pressure downstream climbing up, the pre-combustion shock trains and the flame region move against the stream and the whole fuel jet is ignited and stabilized in a ‘jet surrounding mode’. The expand angle of the upper wall and the disturbance caused by the upstream cavity have an obvious effect on the fuel diffusion and convection procedure into the cavity and further affect the ignition. Hydrogen fuel injected into the cavity directly could improve the ignition performance greatly at the experimental status.

Gouji Yamada - One of the best experts on this subject based on the ideXlab platform.

  • shock tube study of nonequilibrium plasma flows in a mars entry Flight Condition
    31ST INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS: RGD31, 2019
    Co-Authors: Gouji Yamada, Wataru Kaise, Masashi Umezawa
    Abstract:

    In the present study, characteristics of nonequilibrium plasma flows in a Mars entry Flight Condition are investigated by spectroscopic measurements and numerical analysis. A shock tube facility is used to simulate a hypersonic shock wave around a space vehicle entering the Martian atmosphere. From the measured spectra, the emission of the CN violet bands is found to be strong in the measured wavelength range. The rotational and vibrational temperatures are evaluated by a spectrum fitting method and compared with the calculated ones obtained by numerical analysis. It is found that the agreement between experiment and calculation is better as the distance from the shock front increases, where the thermochemical equilibrium is considered to be established, showing that the validity of the physical model applied in the CFD code in the equilibrium region. However, significant disagreement can be seen in the region ahead of the shock front, where the thermochemical processes are not incorporated in the CFD code. Further investigations are required to clarify the thermochemical processes ahead of the shock wave and the improved physical model should be developed.

  • thermochemical process of nonequilibrium plasma flows in a mars entry Flight Condition
    13-TH NATIONAL CONGRESS ON THEORETICAL AND APPLIED MECHANICS, 2017
    Co-Authors: Gouji Yamada, Shouhei Yanai
    Abstract:

    Experimental and numerical studies are conducted to investigate characteristics of shock-induced plasma flows around a space vehicles entering into the Mars atmosphere. In this study, a shock tube is used to simulate a shock wave generated around a space vehicle in a Mars entry Flight Condition. Spectroscopic measurements of the plasma flows are conducted behind a shock wave generated in the shock tube. Measured spectra show the chemical composition of plasma flows and temporal evolution of chemical reaction processes. It is found that emissions of CN and C2 molecules are dominant in the measured spectra. The rotational and vibrational temperetures are derived from the measured spectra by a spectrum fitting technique and compared with the numerical ones obtained from the computational fluid dynamics (CFD) simulation. It is found that the measured rotational and vibrational temperatures are almost same immediately behind a shock wave, showing the disagreement with the calculated ones. The present result has indicated that the modification of the physical model used in the simulation is required by further investigations.

Masaru Uchiyama - One of the best experts on this subject based on the ideXlab platform.

  • Flight control systems of a quad tilt rotor unmanned aerial vehicle for a large attitude change
    International Conference on Robotics and Automation, 2015
    Co-Authors: Atsushi Oosedo, Satoko Abiko, Shota Narasaki, Atsushi Kuno, Atsushi Konno, Masaru Uchiyama
    Abstract:

    Quad tilt rotor Unmanned Aerial Vehicle (UAV) solves the problem of underacuated system in general quadrotor UAV. The quad tilt rotor UAV can control position and attitude independently by tilting directions of propellers. However, the Flight control system in a wide range of attitudes has not been discussed yet, e.g. a UAV flying and hovering with a 90 [°] pitch angle and can flip over when the range of the tilting motor rotates wide enough. In this paper, we present the attitude transition Flight control system for pitch angles ranging 0 [°] to 90 [°] since Flight Condition with a 90 [°] pitch angle significantly differs from that in a conventional quadrotor UAV Flight, and then adequate control system and sufficient experimental validation are necessary for stable Flight in a wide range of attitude Conditions.