Yongbin Ji

Effect of crossflow regulation by varying jet diameters in streamwise direction on jet impingement heat transfer under maximum crossflow condition

ABSTRACT Jet impingement heat transfer has been studied numerically for a maximum crossflow condition using a 3 × 9 array of jets. Five-hole configurations have been studied for jet average Reynolds numbers ranging from 10,000 to 20,000. Crossflow has been mitigated by varying the jet diameters in the streamwise direction to reduce the impact of crossflow on downstream jet impingement. The design criteria for all five configurations were to keep the average of the jet diameters equal to the constant jet diameter configuration (baseline). It has been found that the configuration with increasing and then decreasing jet diameters provided higher levels of heat transfer with more uniform cooling when compared to the traditional constant diameter configuration and other configurations.

Numerical Investigation of Scoop Effect on Film Cooling for Cylindrical Inclined Hole

Film cooling behavior of a single cylindrical hole inclined at an angle of 35° with respect to a flat surface is numerically predicted in this study. Adiabatic film cooling effectiveness has been presented to evaluate the influence of the scoop placed on the coolant entry side. The effect of blowing ratio (0.65, 1, 1.5 and 2) and the length-to-diameter ratio (1.7 and 4.4) are examined. Three-dimensional Reynolds-averaged Navier-Stokes analysis with SST turbulence model is used for the computations. It has been found that both centerline and laterally averaged adiabatic film cooling effectiveness are enhanced by the scoop and the enhancement increases with the blowing ratio in the investigated range of variables. The scoop was more effective for the higher length-to-diameter ratio cases (L/D = 4.4) because of better velocity distribution at the film hole exit, which makes coolant reattach at a more upstream location after blowing off from the wall.Copyright

Comparative Study of Impinging Jet Array Heat Transfer on a Flat Plate Cooled by Superheated Steam and Air

In modern gas turbine, using superheated steam to cool the vane and the liner of combustion chamber is a promising alternative to traditional compressor air. Infrared camera was applied to measure the spatial distribution of the impingement heat transfer coefficient on a flat plate cooled by superheated steam and air in this paper. The experimental study revealed the distribution of local heat transfer coefficients over a flat plate cooled by steam and air in an array of 3×5 impinging jets module. Results showed that the impingement cooling heat transfer is enhanced by the increase of mass flow rate, and the superheated steam cooling could improve area averaged heat transfer performance 35.3∼83.0% more than air cooling in the same mass flow rate conditions in the experiment. The influence of the jet-to-plate spacing ratio (Zn/d) and the jet-to-jet spacing ratio (Yn/d) on heat transfer were also investigated. It was concluded that the heat transfer is enhanced with the increase of Yn/d or the decrease of Zn/d based on the same area. Furthermore, three-dimensional and steady state computations had been carried out for experimental operating conditions. The Numerical results and experimental data have good agreements with each other for both the area averaged Nu and the local Nu, so results of the numerical model are expecting reliable. Results based Numerical models showed detailed characteristics of the distribution of the velocity and turbulence level, which revealed underlying mechanisms of pressure loss and flow structure for steam cooing and air cooling respectively.© 2014 ASME