Flow structure due to hexagonal cavities and bumps on a plate surfaceButt, U.;Egbers, C.
2016 Thermophysics and Aeromechanics
doi: 10.1134/S0869864316060068
Abstract We present the results of flow visualization and velocity measurements on a hexagonal structured surface. Several configurations with concave and convex hexagonal structures are investigated. Each hexagonal structure is 2.7 mm deep and 33 mm wide (width between flats) and has a height to diameter ratio of 0.05 based on equivalent diameter. Considered are flow velocities 19 m/s, 24 m/s, and 27 m/s. The flow bifurcates on the leading edge of the concave configuration into two counter rotating vortices and propagates further in streamwise direction. The circulating regions are identified by the peaks in r.m.s. velocity curves. In case of concave configuration, the flow splits up into counter rotating vortical structures in a vertical plane parallel to the flow. The lower vortex rotating in the opposite direction of the flow cause the oil film fringes to drift upstream. Complex circulating regions similar to the arrangement of slices in an orange can be observed on the trailing edge of the concave hexagonal structure.
Expansion of capabilities of the short-duration wind tunnel with an opposing pressure multiplierShumskii, V. V.;Yaroslavtsev, M. I.
2016 Thermophysics and Aeromechanics
doi: 10.1134/S086986431606007X
Abstract A method for raising the maximum settling-chamber pressure in a short-duration wind tunnel equipped with pressure multipliers arranged in opposition to each other for stabilization of test gas parameters is proposed. For this purpose, a wind-tunnel design with an additional third pressure multiplier attached to the body of the second pressure multiplier was developed. The rod of the additional multiplier contacts the large-area piston stage of the second multiplier, and the pre-piston space being connected to the receiver. The inclusion of an additional pressure multiplier in the wind-tunnel design at the maximum attainable driver-gas pressure of 150−170 bar, defined by the standard industrial pressure of air used for filling wind-tunnel receivers with the driver gas, allows a two-fold increase in the maximum settling-chamber pressure, from 1100 to 2000−2200 bar. For raising the maximum settling-chamber pressure above 2000–2200 bar, the use of one additional pressure multiplier proved to be insufficient because, in the latter case, its becomes necessary to simultaneously raise the driver-gas pressure over 150−170 bar.
Heat exchange at laminar flow in rectangular channelsValueva, E. P.;Purdin, M. S.
2016 Thermophysics and Aeromechanics
doi: 10.1134/S0869864316060081
Abstract Numerical modeling of heat exchange at a laminar stationary and pulsatile flow in rectangular channels with different aspect ratios of side lengths γ has been carried out by a finite difference method for two boundary conditions: a constant wall temperature and a constant heat flux density on the wall. For the boundary condition of the first kind, the similarity of distributions of the heat flux density and shear stress on the walls over the channel perimeter has been established. The reasons for a nonmonotonous dependence of the initial thermal interval length on γ are discussed. For the boundary condition of the second kind, the difference of the Nusselt number averaged over the perimeter at γ → 0 from its value for a flow in a flat channel has been explained. An increase in the Nusselt number averaged over the perimeter and the period of oscillations has been revealed for a pulsatile flow in the quasi-stationary regime at large amplitudes of the oscillations of the velocity averaged over the cross section.
Peculiarities of evolution of shock waves generated by boiling coolantAlekseev, M. V.;Vozhakov, I. S.;Lezhnin, S. I.;Pribaturin, N. A.
2016 Thermophysics and Aeromechanics
doi: 10.1134/S0869864316060093
Abstract Simulation of compression wave generation and evolution at the disk target was performed for the case of explosive-type boiling of coolant; the boiling is initiated by endwall rupture of a high-pressure pipeline. The calculations were performed for shock wave amplitude at different times and modes of pipe rupture. The simulated pressure of a target-reflected shock wave is different from the theoretical value for ideal gas; this discrepancy between simulation and theory becomes lower at higher distances of flow from the nozzle exit. Comparative simulation study was performed for flow of two-phase coolant with account for slip flow effect and for different sizes of droplets. Simulation gave the limiting droplet size when the single-velocity homogeneous flow model is valid, i.e., the slip flow effect is insignificant.