Yuichi Mitsutake

Analysis of viscous micropump with single rotating cylinder

This study presents the transient nature and performance of viscous micropump for low Reynolds number where flow is assumed laminar, unsteady, incompressible and two dimensional. The device consists of a cylinder placed eccentrically inside an extremely narrow channel, where channel axis is perpendicular to cylinder axis. When the cylinder rotates, it generates a net force on fluid due to unequal shear stresses on the top and bottom surfaces of the cylinder. This net force is capable of generating a net flow against a pressure gradient. The flow field inside the micro channel has been analyzed by using structured grid Finite Volume Method (FVM) based on Navier-Stokes equation. All parameters used in flow simulation are expressed in non-dimensional quantities for better understanding of flow behavior, regardless of dimensions or the fluid that is used. The effect of the channel height (S), the cylinder eccentricity (e), the Reynolds number (Re) and Pump load (P*) have been studied. Various flow patterns inside the micro pump as well as variations in flow velocity with time are obtained. Both the steady state and transient results of viscous micro pump are validated. It is found that the average velocity of fluid increases with increasing cylinder eccentricity and decreases with increasing the channel height.

A computational study on oblique shock wave-turbulent boundary layer interaction

A numerical computation of an oblique shock wave incident on a turbulent boundary layer was performed for free stream flow of air at M∞ = 2.0 and Re1 = 10.5×106u2005m−1. The oblique shock wave was generated from a 8° wedge. Reynolds averaged Navier-Stokes (RANS) simulation with k-ω SST turbulence model was first utilized for two dimensional (2D) steady case. The results were compared with the experiment at the same flow conditions. Further, to capture the unsteadiness, a 2D Large Eddy Simulation (LES) with sub-grid scale model WMLES was performed which showed the unsteady effects. The frequency of the shock oscillation was computed and was found to be comparable with that of experimental measurement.

On the prediction of explosive boiling characteristics in superheated liquid during non-equilibrium heating: Continuum modeling vs. atomistic-continuum modeling

With the recent advancement in the field of micro electro mechanical systems (MEMS), where actuation is used, researchers are in pursuit of using the energy released by explosive boiling phenomenon. Though many experimental works have been conducted on this phenomenon in the past, there have been very few theoretical works based on equilibrium nucleation theory that are unable to predict the time at which explosive boiling will occur when liquid is subjected to non-uniform transient heating. Recently two theoretical models based on two different approaches have been reported for transient non-equilibrium heating of liquid. One of the models is based on continuum assumption in which macroscopic properties of liquid together with heating condition govern the explosive boiling characteristics. The other model considers long range inter molecular forces between liquid and solid heater surface in addition to the continuum assumptions and therefore might be considered as atomistic-continuum model. In the presen...

Oblique shock wave interaction with turbulent boundary layer over a wavy surface

A numerical computation was performed of an oblique shock wave impinging on turbulent boundary layer developing on a flat surface. The free stream flow was at M∞ = 2.0 with unit Reynolds number, Re = 10.5×106 m-1. A wedge having an angle of 8° with the free stream flow was used to generate the oblique shock wave. Three dimensional Reynolds averaged Navier-Stokes (RANS) steady simulation with k-ω SST turbulence model was used. The numerically obtained results were validated with experimental data obtained at same flow conditions. Periodic waviness was introduced to a portion of the wall to investigate its effect on shock wave turbulent boundary layer interaction. The geometry of wall waviness was characterized by amplitude and number of cycles. Different cases were studied by varying the amplitude of waviness. The presence of wall waviness affected shock structure and flow separation patterns. Variations of flow properties with respect to waviness amplitude were also studied.

Effect of cavity on shock oscillation in transonic flow over RAE2822 supercritical airfoil

Transonic flow past a supercritical airfoil is strongly influenced by the interaction of shock wave with boundary layer. This interaction induces unsteady self-sustaining shock wave oscillation, flow instability, drag rise and buffet onset which limit the flight envelop. In the present study, a computational analysis has been carried out to investigate the flow past a supercritical RAE2822 airfoil in transonic speeds. To control the shock wave oscillation, a cavity is introduced on the airfoil surface where shock wave oscillates. Different geometric configurations have been investigated for finding optimum cavity geometry and dimension. Unsteady Reynolds averaged Navier-Stokes equations (RANS) are computed at Mach 0.729 with an angle of attack of 5°. Computed results are well validated with the available experimental data in case of baseline airfoil. However, in case of airfoil with control cavity; it has been observed that the introduction of cavity completely suppresses the unsteady shock wave oscillation. Further, significant drag reduction and successive improvement of aerodynamic performance have been observed in airfoil with shock control cavity.Transonic flow past a supercritical airfoil is strongly influenced by the interaction of shock wave with boundary layer. This interaction induces unsteady self-sustaining shock wave oscillation, flow instability, drag rise and buffet onset which limit the flight envelop. In the present study, a computational analysis has been carried out to investigate the flow past a supercritical RAE2822 airfoil in transonic speeds. To control the shock wave oscillation, a cavity is introduced on the airfoil surface where shock wave oscillates. Different geometric configurations have been investigated for finding optimum cavity geometry and dimension. Unsteady Reynolds averaged Navier-Stokes equations (RANS) are computed at Mach 0.729 with an angle of attack of 5°. Computed results are well validated with the available experimental data in case of baseline airfoil. However, in case of airfoil with control cavity; it has been observed that the introduction of cavity completely suppresses the unsteady shock wave oscillati...