Numerical Simulation of Evaporating Two-Phase Flow in a High-Aspect-Ratio Microchannel with Bends

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Junsik Lee ◽  
Junsub Kim ◽  
Hyungsoo Lim ◽  
Je Sung Bang ◽  
Jeong Min Seo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flow Visualization ◽  
Film Cooling ◽  
High Speed ◽  
National Research Council ◽  
Air Cooling ◽  
Hole Size ◽  
High Efficient ◽  
Flow Through ◽  
Effusion Hole

Effusion cooling is one of the attractive methods for next generation high-efficient gas turbine which has a very hot gas temperature above 1,600oC. For higher effectiveness of the air cooling, the air-cooled flow through effusion-holes does not penetrate into the mainstream flow but still remains within freestream boundary layer. So the air-cooled surface temperature maintains at relatively lower than film cooling. Effusion cooling is generally known as operating in small effusion-hole size which is less than 0.2 mm. This study is intended to examine optimum effusion-hole size of the microscale effusion cooling through flow visualization. The air flow through effusion-holes is visualized using an oil atomizer, a DSPP laser-sheet illumination, and a high-speed CCD imaging. The visualized results show flow patterns and characteristics with different blowing ratio, BR = ρcUc / ρ∞U∞, (BR = 0.17 and 0.53) and effusion-hole size (D = 0.2 mm, 0.5 mm and 1.0 mm). The flow visualization condition is fixed at the mainstream Reynolds number of 10,000 and hole-to-hole spacing of 4 (S/D = 4). For larger effusion-hole of 1.0 mm [(a) and (b)], the effusion flow can penetrate into boundary layer which exhibits a film cooling. However the effusion flow is observed to be remained within boundary layer which shows an effusion cooling for smaller effusion-hole of 0.2 mm [(e) and (f)]. In case of (c) and (d), a series of vortical structure is also observed to be within the boundary layer along the effusion flat plate. Note that the effusion-hole size of 0.5 mm can be a candidate for making effusion cooling possible. [This work was supported by National Research Council of Science and Technology (NST) grant funded by the Ministry of Science, ICT and Future Planning, Korea (Grant No. KIMM-NK203B).]

Downstream Influence of Film-Cooling in a High-speed Laminar Boundary Layer

AIAA Journal ◽  
1973 ◽  
Vol 11 (5) ◽  
pp. 581-582 ◽  
Author(s):  
ANTHONY L. LAGANELLI ◽  
RICHARD P. FOGAROLI
Keyword(s):  
Boundary Layer ◽  
Laminar Boundary Layer ◽  
Film Cooling ◽  
High Speed

A Visual Study of Turbine Blade Pressure-Side Boundary Layers

1983 ◽  
Vol 105 (1) ◽  
pp. 47-52 ◽  
Author(s):  
L. S. Han ◽  
W. R. Cox
Keyword(s):  
Boundary Layer ◽  
Flow Visualization ◽  
Boundary Layers ◽  
Turbine Blade ◽  
High Speed ◽  
High Speed Photography ◽  
Pressure Side ◽  
Edge Region ◽  
Visual Study ◽  
Blade Cascade

Boundary layer characteristics on the pressure-side of a turbine airfoil were investigated experimentally in a three-blade cascade tunnel. The blades had a chord length of 21 in. to facilitate flow visualization and high-speed photography. The investigation revealed the existence of the Gortler’s vortices appearing in spurts in regions of severe curvature. In the trailing edge region, Karman vortices were detected and found to interact strongly with the Gortler’s vortices convected thereto.

scholarly journals A Visual Study of Turbine Blade Pressure-Side Boundary Layers

1982 ◽  
Author(s):  
Lit S. Han ◽  
W. R. Cox
Keyword(s):  
Boundary Layer ◽  
Flow Visualization ◽  
Boundary Layers ◽  
Turbine Blade ◽  
High Speed ◽  
High Speed Photography ◽  
Pressure Side ◽  
Edge Region ◽  
Visual Study ◽  
Blade Cascade

Boundary layer characteristics on the pressure-side of a turbine airfoil were investigated experimentally in a three-blade cascade tunnel. The blades had a chord length of 21 in. to facilitate flow visualization and high-speed photography. The investigation revealed the existence of the Gortler’s vortices appearing in spurts in regions of severe curvature. In the trailing edge region, Karman vortices were detected and found to interact strongly with the Gortler’s vortices convected thereto.

Flow Visualization of Microscale Effusion and Transpiration Cooling on Semi-cylinder for Gas Turbine Cooling Application

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Dong Hwan Shin ◽  
Yeonghwan Kim ◽  
Jin Sub Kim ◽  
Do Won Kang ◽  
Jeong-Lak Sohn ◽  
...  
Keyword(s):  
Flow Visualization ◽  
Gas Turbine ◽  
Metal Surface ◽  
Flow Behavior ◽  
Porous Metal ◽  
Air Cooling ◽  
Transpiration Cooling ◽  
Turbine Cooling ◽  
High Efficient ◽  
Gas Turbine Cooling

Abstract Effusion and transpiration cooling can be an attractive method of air cooling for the next generation high-efficient gas turbine which has a very hot gas temperature over 1,600°C (TRIT). For higher effectiveness of air cooling for a gas turbine vane and blade, the air-cooled flow through effusion-holes and porous metal surface should not penetrate into the mainstream flow but still remain within the thermal boundary layer. The present visualization study examines flow behavior of microscale effusion and transpiration cooling on semi-cylinder. The secondary flow issued from the effusion-holes and porous metal surface is visualized by a smoke-tube method which consists of oil droplet generator, diode pumped solid state (DPSS) laser and highspeed imaging. The flow visualization of microscale effusion and transpiration cooling on semi-cylinder is characterized with various blowing ratios. It is found that the transpiration cooling consumes less coolant air than effusion cooling and has better cooling effectiveness based on the same flow rate of coolant air. Visual criteria can be provided to maintain the effusion and transpiration cooling on semi-cylinder for gas turbine cooling application. [This work was supported by the National Research Council of Science and Technology (NST) grant funded by the Ministry of Science and ICT, Korea (Grant No. KIMM-NK219B).]

Water Flow Visualization in a Converging-Diverging Glass Nozzle

2016 ◽  
Author(s):  
Aaron Schmidt ◽  
B. Terry Beck ◽  
Mohammad H. Hosni
Keyword(s):  
Flow Visualization ◽  
Flow Velocity ◽  
High Speed ◽  
Digital Camera ◽  
High Speed Camera ◽  
Nozzle Throat ◽  
Glass Spheres ◽  
Seed Particles ◽  
Flow Through ◽  
Nozzle Inlet

Water flow through a converging-diverging glass nozzle experiences a pressure drop and its velocity increases as it flows through the converging section. For an inviscid fluid, the pressure minimum occurs at the nozzle throat, where the cross-sectional area is minimum. If the minimum pressure is below the water vapor pressure, cavitation may occur. Viscous fluid flow through a converging-diverging nozzle experiences more complex flow patterns. Additionally, fluid through the nozzle may be driven into the metastable region and subsequently cavitate at a lower pressure than the vapor pressure. The dynamic conditions that trigger cavitation in a converging-diverging nozzle are not well understood; moreover, direct measurements involving invasive probe insertion in the region of cavitation onset can induce cavitation. The study of a glass converging-diverging nozzle allowed for noninvasive flow visualization and quantitative observational measurements to be made. A high-speed digital camera was used to capture qualitative and quantitative information on the flow pattern inside the nozzle. The transient time period during cavitation onset was visualized at 35,000 frames per second. Video from the high-speed digital camera revealed that the cavitation front began approximately one nozzle throat diameter downstream from the nozzle throat. Small glass sphere seed particles and injected bubbles were used to trace flow through the nozzle and measure flow velocity at different locations in the nozzle. Small injected bubbles were tracked using the high-speed camera to measure the flow velocity in the nozzle inlet and converging sections. Glass spheres of 10 μm and 120 μm diameter were introduced to the flow to visualize the flow inside the nozzle and track flow velocity. The 120 μm glass spheres were visible using the high-speed camera and were tracked to measure flow velocity in the converging and throat regions of the nozzle. The 120 μm spheres were large enough to provide nucleation sites for cavitation and were seen to trigger cavitation near the nozzle throat. The cavitation induced by the glass spheres occurred upstream of the cavitation front previously observed in the absence of the spheres at identical nozzle inlet and outlet pressures. This shift in the cavitation front suggested the presence of metastable flow through the nozzle throat in the absence of seed particles. The 120 μm spheres also revealed that the flow had separated from the nozzle wall downstream of the nozzle throat. Tracking bubbles produced by the cavitation front also permitted flow visualization of the regions of separated flow, which first separated from the wall upstream of the cavitation front. Flow visualization of cavitation in the converging-diverging glass nozzle obtained by the high-speed digital camera provided valuable information regarding the conditions that lead to cavitation. High-speed imaging revealed the dynamic fluid behaviors during the onset of cavitation. Bubble and seed particle tracking provided velocity information at several locations throughout the nozzle. Visualization of the entire region of cavitation allowed for the measurement of the cavitation region length, which varied depending upon the nozzle outlet pressure.

Film Cooling With Normal Injection Into a Supersonic Flow

1968 ◽  
Vol 90 (4) ◽  
pp. 584-588 ◽  
Author(s):  
R. J. Goldstein ◽  
E. R. G. Eckert ◽  
D. J. Wilson
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
High Speed ◽  
Incompressible Flows ◽  
Free Stream ◽  
Gas Injection ◽  
Adiabatic Wall ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Good Agreement

An experimental study of film cooling with subsonic gas injection into a mainstream with a Mach number of 2.90 is reported. Air, used as both the mainstream and secondary fluids, is injected normal to the surface of a flat plate through a short porous section into a two-dimensional turbulent boundary layer. The secondary fluid enters the boundary layer with a mass velocity which ranges from 0.0085 to 0.0223 of the free-stream value. The adiabatic wall temperatures are presented as the film-cooling effectiveness. The results of the present study, when the proper choice is made for the reference state used to account for fluid property variations across the high-speed boundary layer, are in good agreement with previous investigations in incompressible flows.

A Statistical Study of Process Variables to Optimize a High Speed Curtain Coater: Part I

TAPPI Journal ◽  
2009 ◽  
Vol 8 (1) ◽  
pp. 20-26 ◽  
Author(s):  
PEEYUSH TRIPATHI ◽  
MARGARET JOYCE ◽  
PAUL D. FLEMING ◽  
MASAHIRO SUGIHARA
Keyword(s):  
Boundary Layer ◽  
Experimental Design ◽  
High Speed ◽  
Statistical Study ◽  
Process Variables ◽  
High Speeds ◽  
The Stability ◽  
Air Removal ◽  
Removal System

Using an experimental design approach, researchers altered process parameters and material prop-erties to stabilize the curtain of a pilot curtain coater at high speeds. Part I of this paper identifies the four significant variables that influence curtain stability. The boundary layer air removal system was critical to the stability of the curtain and base sheet roughness was found to be very important. A shear thinning coating rheology and higher curtain heights improved the curtain stability at high speeds. The sizing of the base sheet affected coverage and cur-tain stability because of its effect on base sheet wettability. The role of surfactant was inconclusive. Part II of this paper will report on further optimization of curtain stability with these four variables using a D-optimal partial-facto-rial design.

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