The objective of this study is to improve the performance of the sensitivity-adjustable three component force balance developed in the previous study for the usage of various experimental conditions. In the present study, balance shape is modified from the previous oval-shape to hexagonal-shape. First, the strain distribution for three kinds of balance shapes is deduced by FEM analysis to decide the strain gauge paste positions and the validity is confirmed by force balance calibration. Then, the characteristics of the sensitivity adjustability are investigated by FEM analysis and force balance calibration for various kinds of balance shapes. Finally, a hexagonal force balance is designed and applied to the wind tunnel experiment in a supersonic flow condition which is one of the severe experimental conditions. As a result, the use of hexagonal-shape enables us to improve the measurement accuracy because to paste strain gauges on appropriate positions is much easier for hexagonal-shape than for oval-shape. In addition, we can adjust the sensitivity ratio more extensively for hexagonal-shape than for oval-shape. The designed hexagonal force balance can measure aerodynamic forces in a supersonic flow condition. In conclusion, we can improve the performance of the sensitivity-adjustable three component force balance by the use of hexagonal-shape and apply to a supersonic wind tunnel experiment. In future, force balance calibration to investigate dynamic characteristics is required for a supersonic wind tunnel experiment.
In this study, a cooling device using supersonic flow inside a micro-channel has been evaluated. To confirm the density measurement and temperature estimation of the supersonic air flow inside a micro-channel, a preliminary experiment using an interferometer was conducted. A single micro-channel was fabricated in a small Si plate, which was made using Micro-Electro-Mechanical System (MEMS) technology. The channel size was approximately 200 μm in width, 500 μm in depth, and 6000 μm in length. The Deep Reactive-Ion-Etching (Deep-RIE) method was used for fabricating of the channel. A fabricated Si plate was sandwiched between glass plates. The density field of the supersonic/subsonic air flow near inlet and outlet were recorded as phase-shifted data using a phase-shifting interferometer. The pressure at the inlet, outlet, and inside the channel were set to 0.7 and 0.1 MPaA, respectively. The density field of the micro-channel air flow was evaluated despite the fringe number being less than one. This experimental result was compared with numerical simulation. From the comparison, the measured density field exhibited a good agreement with the numerical results, and the temperature field could be estimated. It was confirmed that this method was valid for the density measurement and the sophisticated visualization of the supersonic air flow inside a micro-channel.
The purpose of the research is to clarify the generation mechanism of precursor electrons ahead of a hypersonic shock wave in argon. The triple-probe measurements and radiation measurements are carried out using a hypersonic shock tube. Theoretical analysis is also carried out using a one-dimensional photoionization model. The triple-probe measurements show that the electron temperature is almost uniform ahead of the shock wave and ranges from 5000 to 11000 K. In contrast to the electron temperature, the electron density increases exponentially as approaching the shock wave and lies between 1015 and 1017 m-3. These results show that considerable electrons exist in the region ahead of the shock wave. From the radiation measurements, argon ions are found to emit radiation in the region ahead of the shock wave, showing that argon ions are generated from argon atoms by photoionization. The behavior of electron temperature and density is well accounted for by the one-dimensional photoionization model with an assumption of photoionization as the primary ionization process ahead of the shock wave. In conclusion, precursor electrons are mainly generated by photoionization, making use of the radiation energy behind the shock wave.
The subject of this paper is to improve on parameterization for conceptual design method of three stage hybrid rocket. Multi-Objective Genetic Algorithm (MOGA) is employed to solve multi-disciplinary design exploration of a three-stage launch vehicle concept using a hybrid rocket engine. MOGA which is used as the optimization methods for multi-objective problems utilizes real-number cording and the Pareto ranking method. According to our previous study, the propulsive performance of MOGA's solution was as low as the lower limit of design space. The design space of a conceptual three-stage launch vehicle hybrid rocket engine was reconsidered based on the results of multi-disciplinary design optimization. The design variables of the nozzles were reconsidered by exploring the design space. Specifically, the nozzle expansion ratio was considered as the ratio of the nozzle exit radius to the body radius. In this way, there are no solutions which violate the design constraints about the geometric condition of the nozzle exit. Consequently, the new conceptual design method can effectively explore solutions which have higher propulsive performance than previous method. As the result, the combustion chamber pressure is increased in the first stage. In the second stage, the solutions which are explored, modified parameterization are shown larger thrust level than previously.
Low-speed wind tunnel tests are carried out to investigate the control surface effectiveness at low Reynolds numbers (Re = 20,000-80,000). A thick airfoil, NACA0012, has a nonlinearity of the control surface effectiveness, which are associated with flow separation both on the upper and lower surfaces and a formation of a laminar separation bubble. Thin airfoils such as NACA0006 and a 3%c flat plate have a much smaller nonlinearity of the control surface effectiveness. These differences in the control surface effectiveness are due to the nonlinearity of the lift curve for each airfoil, and the flow separation behavior has a profound effect on the control surface effectiveness.
CFD simulations with uniform grids have been paid attention as a next-generation CFD simulation on a large-scale supercomputing system. The Building-Cube Method (BCM) is one of the next-generation CFD methods. The basic idea is to balance loads of calculations among processing elements on a supercomputing system by dividing the whole calculations into many parallel tasks with the same amount of computation. Thus, it is suitable for highly parallel computation on supercomputing systems. This paper firstly implements BCM on five supercomputing systems as an example of a next-generation CFD simulation in the upcoming postpeta-scale era. Then, by theoretical analyses and performance evaluations, this paper clarifies the requirements of future supercomputing systems for a next-generation CFD simulation. The performance evaluations show that as the number of processing elements increases, the imbalance of data exchanges among nodes becomes more serious than that of calculations even in a next-generation CFD simulation. While the calculation time can ideally be reduced according to the number of processing elements, the data transfer time becomes dominant in the total execution time. Different from the massively-parallel system architecture, the number of nodes in a system should be as small as possible to prevent the data transfer. The performance analyses also show that the memory bandwidth limits the performance of BCM and use of an on-chip memory is effective to improve the performance. A memory subsystem that achieves a higher sustained memory bandwidth is required. Therefore, a supercomputing system that consists of a small number of high-performance nodes is essential to achieve high sustained performance of the next-generation CFD in the up coming postpeta-scale era by reducing the data transfers, which becomes eventually a bottleneck in large-scale simulation.
Building Cube Method (BCM) adopts block-structured Cartesian mesh and finer resolution can be used where the flow contains detailed flow structures. This paper reports the recent progress in extending BCM to curvilinear body-fitted mesh with Adaptive Mesh Refinement (AMR). Compared to Cartesian mesh based AMR, body-fitted AMR strategy is more complicated and less studied. In this paper the key components of body-fitted curvilinear mesh based AMR are introduced. A pressure based refinement criterion is used to detect both shock wave and strong vortex. Cubic interpolation is used to preserve the quality of the refined mesh. A sub-block based refinement strategy is also developed for the treatment of singular geometry features. Combined with the high order scheme, an accurate and robust curvilinear mesh based AMR tool is developed with which the flow details can be automatically captured. Numerical examples are given to validate the numerical properties of current AMR tool and to demonstrate the benefits of current body-fitted AMR strategy.
The aim of this research is to evaluate high temperature damage of combustion chamber made of Cu-Cr-Zr alloy using eddy current testing (ECT) techniques based on AMR sensor. The cracks in a simulated combustion chamber can be detected by multi-frequency ECT technique. Also the relative conductivity of damaged copper alloy specimens both at room temperature during tensile testing and at high temperature of fatigue and creep testing were related to the applied damage with micro cracks.
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