Takashi Misaka

Application of Crossflow Transition Criteria to Local Correlation-Based Transition Model

Transition criteria for crossflow instability are investigated in order to apply the γ-Reθ transition model to boundary layer flows with strong three-dimensionality. The criteria are evaluated by comparing their predictions with experimental results for the flowfields around a cylinder at various yaw angles, and the flowfields around a swept wing. It is found that the crossflow criterion proposed by Kohama et al. is a promising one because it can be evaluated by using only local flow variables. Transition prediction of a yawed cylinder has been performed by the γ-Reθ transition model with the proposed crossflow criterion. The production of eddy viscosity due to the present criteria was confirmed. A modification of the criterion was suggested to treat its dependency on flow conditions.

Effect of Camber on Badminton Shuttlecock

In this study, we conducted experimental measurements and computational analysis to investigate the aerodynamics of a shuttlecock, especially the effects of the camber of the shuttle’s skirt. The static aerodynamic coefficient from the experiment showed that the camber of the skirt was able to modify the aerodynamic characteristics. A positive camber, which indicates bending the blade toward the outside, causes a slight increase in lift and a decrease in drag. On the other hand, a negative camber causes an increase in drag, and an insensitive region in the lift and a pitching coefficient of approximately 0° was observed. This result leads to instability in the flight of the shuttlecock. The pressure distribution calculated using computational fluid dynamics revealed that each blade functions as a two-dimensional airfoil. However, in most cases, the blade is in stall condition due to an initial divergence angle of the skirt.

TOPOLOGY OPTIMIZATION USING A KRIGING-ASSISTED GENETIC ALGORITHM WITH A NOVEL LEVEL SET REPRESENTATION APPROACH

Topology optimization is an optimization method which can modify connectivity of an object independently of its predefined topology. In this paper, a global optimization method for topology optimization of flow channels considering fluid and heat transfer using a genetic algorithm is presented. A genetic algorithm (GA) is assisted by the Kriging surrogate model to reduce computational cost required for function evaluation. In the present method, the boundary of a flow channel is represented by a level set function. Topology optimization seldom employs GA since topology optimization requires a large number of design variables for a high degree of freedom for shape and topology representation and GA is not effective to handle such a large scale problem. This paper presents a novel representation method to obtain the distribution of level set function with a reasonable number of design variables. The design variables are given at the scattered control points in the design domain, and the Helmholtz equation is solved in the entire domain. The proposed method is applied to a single-objective optimization problem to maximize heat transfer. As a result, GA found several flow channels, each of which has similar objective function values but with different topology. The result indicates that the objective function is a multi-modal function, which means that a method of population-based multipoint simultaneous exploration such as GA is essential for the present topology optimization problem. Considering minimizing pressure loss of a flow channel as the second objective function, the proposed method is applied to a multi-objective optimization problem. As a result, we confirm that the proposed representation method enables to represent flow channels that balance both objective functions and GA captures the trade-off between two objective functions.