Shin-ichi Satake

Measurements of 3D flow in a micro-pipe via micro digital holographic particle tracking velocimetry

This paper details high time-resolution flow field measurements in a micro-pipe made by a micro digital holographic particle tracking velocimetry (micro-DHPTV) method. The system consists of an objective lens, a high-speed camera and a single high-frequency double pulsed laser. The volume of the system is 409.6 µm × 92 µm × 92 µm. It is illuminated by a laser beam with a pulse length of 58 ns, a resolution time of 100 µs and a repetition rate of 1 kHz. 104 velocity vectors could be obtained instantaneously in the micro-pipe. Particle positions in the three-dimensional field are reconstructed by a computer-generated hologram. The time evolution of a three-dimensional water flow in a micro-pipe of 92 µm inner diameter is obtained successfully using the micro-DHPTV system. The error of reconstruction in the z-direction is evaluated by analysing the traverse of particles on a glass plate and obtaining the velocity error in the z-direction by uncertainty analysis.

Direct numerical simulation of an impinging jet into parallel disks

A direct numerical simulation code with cylindrical geometry has been developed. A direct numerical simulation (DNS) of an impinging round jet into parallel disks is performed for a Reynolds number of 10,000 based on the nozzle exit velocity and the nozzle diameter (D). Mean flow variables, turbulent intensity, pressure distribution and turbulent kinetic energy budgets are obtained at various radial locations. The present DNS results are in fairly good agreement with the two‐dimensional PTV measurements by Nishino and co‐workers in 1996. Some flow features of this impinging round jet regarding a turbulent transition process are discussed.

Direct numerical simulation for laminarization of turbulent forced gas flows in circular tubes with strong heating

The direct numerical simulation (DNS) of turbulent transport for a gas with variable properties has been conducted to grasp and understand the laminarization phenomena caused by strong heating. In this study, the inlet Reynolds number based on a bulk velocity and pipe diameter was taken as Re=4300 as in the experiments by Shehata and McEligot (1998). The measured wall temperature distribution was applied as a thermal boundary condition. The number of computational nodes used in the heated region was 768×64×128 in the z-, r- and φ-directions, respectively. Turbulent quantities, such as the mean flow, temperature fluctuations, turbulent stresses and the turbulent statistics, were obtained via DNS. Predicted mean velocity and temperature distributions and integral parameters agreed well with the experiments. The Reynolds shear stress, indicating turbulent transport of momentum, decreases along the streamwise direction. The cause of this reduction can be considered to be that the fluid behavior changes drastically in the near wall region due to strong heating which induces significant variations of the gas properties and, in turn, acceleration and buoyancy effects. In a visualization of the results, one sees that the vortical structures are primarily suppressed within the first section of the heated region (z/D=0–5) and are not regenerated further downstream.

Direct numerical simulation of turbulent channel flow under a uniform magnetic field for large-scale structures at high Reynolds number

A direct numerical simulation (DNS) of turbulent channel flow with high Reynolds number has been carried out to show the effects of the magnetic field. In this study, the Reynolds number for channel flow based on bulk velocity Ub, viscosity ν, and channel width 2δ was set to be constant; Reb=2δUb∕ν=45818. A uniform magnetic field was applied in the direction of the wall normal. The value of the Hartmann number, Ha were 32.5 and 65, where Ha=2δB0σ∕ρν. The turbulent quantities such as the mean flow, turbulent stress, and turbulent statistics were obtained by DNS. Although the influence of the magnetohydrodynamic dissipation terms in the turbulent kinetic energy budget was small, large-scale turbulent structures, e.g., vertical structures, low-speed streaks, ejection, and sweep, were found to decrease at the central region of the channel. Consequently, the difference between production and dissipation in the turbulent kinetic energy decreased with increasing Hartmann number at the central region and large-sc...

High Reynolds Number Computation for Turbulent Heat Transfer in a Pipe Flow

Turbulent transport computations for fully-developed turbulent pipe flow were carried out by means of a direct numerical simulation (DNS) procedure. To investigate the effect of Reynolds number on the turbulent sturcures, the Reynolds number based on a friction velocity and a pipe radius was set to be ReΤ = 150, 180, 360, 500, 1050. The number of maximum computational grids used for ReΤ = 1050 is 1024 × 512 × 768 in the z-, r-and Φ -directions, respectively. The friction coefficients are in good agreement with the empirical correlation. The turbulent quantities such as the mean flow, turbulent stresses, turbulent kinetic energy budget, and the turbulent statistics were obtained. It is found that the turbulent structures depend on these Reynolds numbers.

Parallel computing of a digital hologram and particle searching for microdigital-holographic particle-tracking velocimetry.

We have developed a parallel algorithm for microdigital-holographic particle-tracking velocimetry. The algorithm is used in (1) numerical reconstruction of a particle image computer using a digital hologram, and (2) searching for particles. The numerical reconstruction from the digital hologram makes use of the Fresnel diffraction equation and the FFT (fast Fourier transform), whereas the particle search algorithm looks for local maximum graduation in a reconstruction field represented by a 3D matrix. To achieve high performance computing for both calculations (reconstruction and particle search), two memory partitions are allocated to the 3D matrix. In this matrix, the reconstruction part consists of horizontally placed 2D memory partitions on the x-y plane for the FFT, whereas, the particle search part consists of vertically placed 2D memory partitions set along the z axes. Consequently, the scalability can be obtained for the proportion of processor elements, where the benchmarks are carried out for parallel computation by a SGI Altix machine.

Digital Holographic Particle Tracking Velocimetry for 3-D Transient Flow around an Obstacle in a Narrow Channel

Digital holographic particle tracking velocimetry (PTV) is developed by single high-speed camera and single double pulsed laser with high frequency pulses. This system can directly capture 1000 hologram fringe images for 1 second through a camera computer memory. The 3-D particle location is made of the reconstruction by using a computer hologram algorithm in a personal computer. This system can successfully be applied to instantaneous 3-D velocity measurement in the water flow with a square obstacle, and can obtain an average of 300 instantaneous velocity vectors.

Special purpose computer system for flow visualization using holography technology

We have designed a special purpose computer system for visualizing fluid flow using digital holographic particle tracking velocimetry (DHPTV). This computer contains an Field Programmble Gate Array (FPGA) chip in which a pipeline for calculating the intensity of an object from a hologram by fast Fourier transform is installed. This system can produce 100 reconstructed images from a 1024 x 1024-grid hologram in 3.3 sec. It is expected that this system will contribute to fluid flow analysis.

Experimental investigation of turbulent heat transfer of high Prandtl number fluid flow under strong magnetic field

Abstract An investigation of MHD effects on Flibe simulant fluid (aqueous potassium hydroxide solution) flows has been conducted under the U.S.-Japan JUPITER-II collaboration program using “FLIHY” pipe flow facility at UCLA. Mean and fluctuating temperature profiles in a conducting wall pipe were measured for low Reynolds number turbulent flows using a thermocouples probe at constant heat flux condition. It is suggested that the temperature profiles are characterized by interaction between turbulence production, turbulence suppression due to magnetic field and thermal stratification occurred even under the situation where quite small temperature difference exists in the pipe cross-section.

Direct numerical simulation of turbulent heat transfer in an axially rotating pipe flow

A direct numerical simulation with turbulent transport of a scalar quantity has been carried out to grasp and understand a laminarization phenomena caused by a pipe rotation. In this study, the Reynolds number, which is based on a bulk velocity and a pipe diameter, was set to be constant; Reb=5283, and the rotating ratios of a wall velocity to a bulk velocity were set to be 0.5, 1.0, 2.0 and 3.0. A uniform heat‐flux was applied to the wall as a thermal boundary condition. Prandtl number of the working fluid was assumed to be 0.71. The number of computational grids used in this study was 256×128×128 in the z‐, r‐ and ϕ‐ directions, respectively. The turbulent quantities such as the mean flow, temperature fluctuations, turbulent stresses and pressure distribution and the turbulent statistics were obtained. Moreover, the Reynolds stress and the scalar flux budgets were also obtained for each rotating ratio. The turbulent drag decreases with the rotating ratio increase. The reason of this drag reduction can be considered that the additional rotational production terms appear in the azimuthal turbulence component. The contributions of convection and production terms to the radial scalar flux budget and also to the balance with temperature‐pressure gradient term are significant. The dissipation and viscous diffusion terms are negligible in higher rotating ratio.