No abstract

The heat transfer and the fluid dynamics characteristics of subsonic gas flows through microchannels are examined using the direct simulation Monte Carlo (DSMC) method. A simple implicit treatment for the low-speed inflow and outflow boundaries for the DSMC of the flows in microelectromechanical systems (MEMS) is used. Micro-Couette flows and micro-Poiseuille flows are simulated with the value of the Knudsen numbers ranging between 0.06 and 0.72. Where appropriate, the calculated velocity slip and temperature distribution are compared with analytical solutions derived from the Navier-Stokes equations with slip-boundary conditions. A patterned microstructure with nonuniform surface temperature is also simulated. The computational results show that the Knudsen number and the geometric complexity have significant effects on the heat transfer as well as the fluid dynamics properties of the microfluid flows studied.

No abstract

The frequencies of the bursting events associated with the streamwise coherent structures of spatially developing incompressible turbulent boundary layers were predicted. The structures were modeled as wavelike disturbances associated with the turbulent mean flow using a direct-resonance theory. Global numerical solutions for the resonant eigenmodes of the Orr-Sommerfeld and the vertical vorticity equations were developed. The global method involves the use of second and fourth order accurate finite difference formulae for the differential equations as well as the boundary conditions. The predicted resonance frequencies were found to agree very well with previous results using a local shooting technique and measured data. Ã = boundary layer displacement thickness = mode shape for the x-component of vorticity # = kinematic viscosity 3 = frequency 3 = 3# u 2

No abstract