This study aims to improve the performance of the vertical axis wind turbine using a J-type airfoil shape. In this study we used an optimal airfoil shape called Opt-VF that was obtained in previous research using an optimization method of the Kriging surrogate model approach. We aimed to improve the performance of the optimal airfoil utilizing the J-type airfoil shape, by the realization of good balance to utilize lift and drag forces. 2D computational fluid dynamics (CFD) simulations and experimental performance measurements were performed to confirm the efficiency of the J-type airfoil designs. We designed/evaluated various types of the Jtype airfoils to find the most efficient condition for the optimal airfoil. We also performed flow visualizations to observe the difference between the original and J-type airfoils in detail. Some J-type airfoils achieved better performance than the original optimal airfoil, by generating higher pressure in the inner side of the J-type airfoil and obtaining higher velocity wind flow around the leading edge at certain rotational angles. Finally, experimental evaluations were conducted to compare with the CFD results. Same trends could be confirmed between the CFD and experimental results. In the experimental evaluations, maximum values of power coefficient were increased about 7% and 4% at the cases of two-blades and three-blades, respectively, compared to the original Opt-VF airfoil. These results demonstrated the effectiveness introducing the J-type airfoil shape in the optimal airfoil.

A thermal protection makes one of the biggest technical concerns for a reusable hypersonic flight vehicle. A regenerative cooling using fuel should be promising candidate to clear this problem. In general, a liquid hydrocarbon fuel has worse cooling capability than cryogenic fuel like liquid hydrogen. If the thermal decomposition can be utilized, the cooling ability of the liquid hydrocarbon fuel must be improved. To develop the hypersonic flight vehicle with regenerative cooler, the model predicting its endothermic performance is required. The present study tried to simulate the thermal decomposition of the n-dodecane using Computational Fluid Dynamics (CFD) with chemical reaction models. The n-dodecane is the surrogate material of the kerosine-type jet fuel in academical use. First, fuel-heating tests were performed, to collect the reference data of the thermal decomposition characteristics of the n-dodecane sample fluid, for the numerical simulation. New chemical reaction models were developed by modifying and integrating the existing models. Comparing the results between experiment and reaction calculation showed the necessity to consider the spatial distribution of the physical quantities. To do so, the developed reaction models were combined with two-dimensional CFD. The numerical simulation was conducted to reproduce the reference experiments. The developed model accurately predicts the experimental temperature condition and some mole fractions of the n-dodecane thermal decomposition products. The conversion rate and heat absorption quantity given by the thermal decomposition, on the other hand, were underestimated by the simulation. The prediction errors should be coming from the approximation of the physical properties. The n-dodecane and its thermal decomposition products took the supercritical state in the experiment, but their physical quantities were approximated by the ideal gas values in the simulation. Thus, in conclusion, the numerical simulation approximately and/or partially considering supercritical state should be conducted for the future work.

This study conducts experimental and numerical analyses to verify the applicability of the scaling law for time-averaged drag and lift forces on a three-dimensional pitching airfoil in a periodic flow. The experiments were designed to measure the drag and lift forces acting on the pitching airfoil within the periodic flow and the surrounding flow field. The aim was to confirm the feasibility of applying the scaling law to the experimental results and to validate the numerical calculations. The numerical calculations aimed to obtain the airfoil surface pressure field, which is difficult to measure experimentally, to understand the effects of the airfoil’s three-dimensionality. The experiments and numerical calculations varied parameters such as pitching amplitude, phase difference, and aspect ratio. Both experimental and numerical calculations were conducted at a Reynolds number of 4.1×10³. The numerical results showed that pressure changes occurred near the wingtips of the three-dimensional airfoil. The experimental time-averaged drag and lift coefficients confirmed that the scaling law applicable to two-dimensional airfoils could also be applied to three-dimensional airfoils. As the aspect ratio increases, the time-averaged drag and lift coefficients of the airfoil approach those of a two-dimensional airfoil. Similar to the two-dimensional airfoil, larger pitching amplitudes result in greater discrepancies between the scaling law and experimental outcomes.

In this paper, we propose a new optimization procedure for texture design parameters that combines design of experiments and the modified acceleration gradient method. For the design of texture parameters, it is necessary to determine the optimal combination of number, placement angle, spacing and horizontal shape of texture elements. There are many possible combinations of design parameters, so it is necessary to decide select efficiently. In a previous study, we clarified that frictional force can be reduced by varying the texture depth (Arata et al., 2022). In this study, we investigate a method of determining texture design parameters based on design of experiments and the modified acceleration gradient method. Circular and rectangular shapes are generally employed as the horizontal shapes of texture elements, but Maldonado- Cortés et al. (2021) report that an s-shaped texture more effectively reduces the friction coefficient. In this investigation into the reduction of friction coefficient, numerical experiments were performed that included this s-shaped texture.

This study investigates the accuracy of dynamic models in predicting model constants within inviscid flow fields, such as those used in wind farm flow analysis, from the perspectives of identity and turbulent energy conservation accuracy. Specifically, results are compared between tensor-level and vector-level identities, the latter of which includes the calculation of model constants taking into account the errors of differential approximation. The subgrid-scale models employed include the Smagorinsky model and the coherent structure model. The analysis focuses on inviscid flow fields within a three-dimensional periodic domain. Fourth- or second-order spatial accuracy was applied to a coarse computational grid. The results yielded values of a model constant that compensated the resulting energy conservation errors to zero. The statistics of the velocity fluctuation derivatives in the flow fields where the energy conservation errors were compensated were examined. Dynamic model predictions for both identities were then computed for the Smagorinsky and coherent ctructure models and compared with the correct values. The results show that the dynamic model predictions are largely independent of the energy conservation errors, and that the predictions based on the tensor-level identity deviate significantly more from the correct values than those based on the vector-level identity.