Vol 26, No 2 (2019)

Both numerically and experimentally, the possibility of using a combined method to control the incompressible turbulent boundary layer on a symmetric airfoil section of 12-% relative thickness implemented via the blowing/suction of air through a finely perforated section provided on the wing surface part was examined. The study was performed at Reynolds number Re_c = 0.7·10⁶ in the range of angles of attack α = −6 ÷ 6°. The mechanism of action of this flow control method on the aerodynamic characteristics of the wing was identified. An ambiguous pattern of the effect due to blowing/suction from the viewpoint of ensuring a maximum lift, a gain in wing lift-to-drag ratio, and a reduction of wing aerodynamic drag was revealed.

The peculiarities of supersonic unsteady flows forming in the processes of an impulse starting of a wind tunnel including a fore-chamber, a nozzle, a diffuser, and an exhaust tank are considered. The fore-chamber is separated from the flow duct by a thin breakable diaphragm. Before the wind tunnel starting, the gas contained in the exhaust tank is pumped out down to a very small pressure, and then the high-pressured working gas is fed into the fore-chamber. Upon reaching some value of this pressure, the diaphragm “instantaneously” ruptures, and the working gas starts exhausting through the nozzle: a rapid unsteady process of the wind tunnel starting arises. The numerical simulation of the flows forming at the impulse starting of the simplest experimental gas-dynamic facility has been carried out; the facility is arranged with a nozzle forming at its exit a two-dimensional supersonic flow with the Mach number of 2.9, and with replaceable diffusers having different relative areas of the throat. The numerical computations of two-dimensional unsteady flows have been carried out using the Reynolds-averaged Navier—Stokes equations and the SST k-ω turbulence model. The flow patterns computed numerically are compared with the data of the optical visualization of the flow obtained in the experimental gas-dynamic facility in the process of its starting.

A physical-mathematical model of cooling and solidification of a liquid film entrained by air along the heated surface of a streamlined body with given distribution of the heat flux density over the surface is developed. An example of model numerical testing with a set of governing parameters characteristic of experiments at an air cooling rig is presented.

The presence of bubbles exerts a strong influence on pressure drop, heat transfer, flow pattern, and many other flow characteristics. Due to the complexity of two-phase flow boiling, it is not easy to carry out experimental research. An experimental setup based on ultrasonic detection method is built up in this paper. The present study investigates bubble size distribution and vapor quality in liquid-gas two-phase flow in a vertical narrow channel with the cross section of 3×20 mm. Bubble size distribution is heavily affected by the heat power and mass flux, which means that different flow patterns show different bubble size distributions. Vapor quality is also obtained by the ultrasonic attenuation method, which is compared to the theoretical calculation. The ultrasonic detection model is mainly applied in the bubble-coalesced flow. As the vapor quality is small, the detection value is close to the theoretical value, and this detection model is suitable for nucleate boiling. As the vapor quality is increased, the deviation is larger. By comparison with the theoretical calculations, it is necessary to modify the ultrasonic detection model to fit different flow patterns, which is helpful to study the liquid entrainment mechanism in the micro-channel (especially when the inner diameter is less than 5 mm) in the future.

An experimental investigation of coinstantaneous heat and mass transfer phenomena between water and air in a counter flow wet cooling tower filled with a new type packing named “FCP-08” is presented in this paper. The packing consisted of foamed ceramic corrugated board with sine waves and surface retention groove is 1.0 m high and have a cross sectional test area of 0.68×0.68 m². The present investigation is focused mainly on the effect of the water/air mass flow ratio on the heat and mass transfer characteristics of the cooling tower, for different inlet water temperatures. The results show that the cooling water range R and the cooling tower efficiency e decrease with the increase of water/air mass flow ratio L/G. Meanwhile, the cooling characteristic coefficient KαV/L slightly decreases with the increase of water/air mass flow ratio and the value is obviously higher than that of other packing investigated before. The expression of cooling characteristic coefficient related to water/air mass flow ratio and inlet water temperature is obtained by linear fitting. The comparison between the obtained results and those found in the literature for other types of packing indicates that cooling performance of the tower with foam ceramic packing is better.

The processes of heat and mass transfer occurring in real furnaces of the industrial TPS’s have been investigated with the aid of advanced methods of the three-dimensional computer modeling. The computational experiments have been done on the study of the aerodynamics of high-temperature flows and heat transfer characteristics at a combustion of a low-grade Karaganda coal of the KR200 brand in the combustion chamber of the BKZ-75 boiler of the Shakhtinsk TPS. As a result of the execution of numerical experiments, the aerodynamic pattern of high-temperature flows as well as the temperature distribution in the main cross sections of the furnace chamber and along its height have been obtained. The radiation heat flux on the combustion chamber walls has been computed by the methods of numerical modeling, which has enabled the determination of the regions of its maximum action on furnace shields. The obtained pattern of the distribution in the furnace space of the heat release intensity at combustion determines the regions of the maximum interaction of the fuel and oxidizer.