Hee-Koo Moon

Heat Transfer in a Two-Pass Rectangular Rotating Channel With 45-deg Angled Rib Turbulators

Experimental heat transfer results are presented in a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90 and 135 deg to the direction of rotational plane). The rib turbulators are placed on the leading and trailing sides at an angle 45 deg to the main stream flow. Both 45-deg parallel and cross rib orientations are studied. The results are presented for stationary and rotating cases at three different Reynolds numbers of 5000, 10,000, and 25,000, the corresponding rotation numbers are 0.21, 0.11, and 0.04. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10 and the inlet wall-to-coolant density ratio (Δρ/ρ) is maintained at 0.115 for all surfaces in the channel. Results show that the rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall results. The heat transfer from the first pass trailing and second pass leading surfaces are enhanced by rotation. However, the first pass leading and the second pass trailing sides show a decrease in heat transfer with rotation. The result show that 45-deg parallel ribs produce a better heat transfer augmentation than 45-deg cross ribs, and a 90-deg channel orientation produces higher heat transfer effect over a 135-deg orientation.

Separate Effects of Mach Number and Reynolds Number on Jet Array Impingement Heat Transfer

Limited available data suggest a substantial impact of Mach number on the heat transfer from an array of jets impinging on a surface at fixed Reynolds number. Many jet array heat transfer correlations currently in use are based on tests in which the jet Reynolds number was varied by varying the jet Mach number. Hence, this data may be inaccurate for high Mach numbers. Results from the present study are new and innovative because they separate the effects of jet Reynolds number and jet Mach number for the purposes of validating and improving correlations that are currently in use. The present study provides new data on the separate effects of Reynolds number and Mach number for an array of impinging jets in the form of discharge coefficients, local and spatially averaged Nusselt numbers, and local and spatially averaged recovery factors. The data are unique because data are given for impingement jet Mach numbers as high as 0.60 and impingement jet Reynolds numbers as high as 60,000, and because the effects of Reynolds number and Mach number are separated by providing data at constant Reynolds number because the Mach number is varied, and data at constant Mach number because the Reynolds number is varied. As such, the present data are given for experimental conditions not previously examined, which are outside the range of applicability of current correlations.

Film Cooling Effectiveness on the Leading Edge Region of a Rotating Turbine Blade With Two Rows of Film Cooling Holes Using Pressure Sensitive Paint

Detailed film cooling effectiveness distributions are measured on the leading edge of a rotating gas turbine blade with two rows (pressure-side row and suction-side row from the stagnation line) of holes aligned to the radial axis using the pressure sensitive paint (PSP) technique. Film cooling effectiveness distributions are obtained by comparing the difference of the measured oxygen concentration distributions with air and nitrogen as film cooling gas respectively and by applying the mass transfer analogy. Measurements are conducted on the first-stage rotor blade of a three-stage axial turbine at 2400 rpm (positive off-design), 2550 rpm (design), and 3000 rpm (negative off-design), respectively. The effect of three blowing ratios is also studied. The blade Reynolds number based on the axial chord length and the exit velocity is 200,000 and the total to exit pressure ratio was 1.12 for the first-stage rotor blade. The corresponding rotor blade inlet and outlet Mach numbers are 0.1 and 0.3, respectively. The film cooling effectiveness distributions are presented along with discussions on the influence of rotational speed (off design incidence angle), blowing ratio, and upstream nozzle wakes around the leading edge region. Results show that rotation has a significant impact on the leading edge film cooling distributions with the average film cooling effectiveness in the leading edge region decreasing with an increase in the rotational speed (negative incidence angle).

Film Cooling Effectiveness on the Leading Edge of a Rotating Film-Cooled Blade Using Pressure Sensitive Paint

Detailed film cooling effectiveness distributions were measured on the leading edge region of a rotating blade using a Pressure Sensitive Paint technique. The film cooling effectiveness information was obtained from the oxygen concentration difference between air and nitrogen or air and CO2 injection cases by applying the mass transfer analogy. The blowing ratio was controlled to be 0.5, 1.0, and 2.0 while the density ratios of 1.0 and 1.5 were obtained using nitrogen and CO2 as coolant gases, respectively. Tests were conducted on the first stage rotor of a 3-stage axial turbine at 2400, 2550, and 3000 rpm. The Reynolds number based on the axial chord length and the exit velocity was 200,000 and the total to exit pressure ratio was 1.12 for the first rotor. The film cooling effectiveness distributions were presented along with the discussions on the influences of blowing ratio, density ratio, and vortices around the leading edge region at different rotational speeds.Copyright

Film Cooling Effectiveness on the Leading Edge of a Rotating Turbine Blade

Detailed film cooling effectiveness distributions were measured on the leading edge region of a rotating blade using a Pressure Sensitive Paint technique. The film cooling effectiveness information was obtained from the oxygen concentration difference between air and nitrogen or air and CO2 injection cases by applying the mass transfer analogy. The blowing ratio was controlled to be 0.5, 1.0, and 2.0 while the density ratios of 1.0 and 1.5 were obtained using nitrogen and CO2 as coolant gases, respectively. Tests were conducted on the first stage rotor of a 3-stage axial turbine with off-design condition at 2400 rpm. The Reynolds number based on the axial chord length and the exit velocity was 200,000 and the total to exit pressure ratio was 1.12 for the first rotor. The film cooling effectiveness distributions were presented along with the discussion on the influence of blowing ratio, density ratio, and vortices around the leading edge region.Copyright

Experimental and Numerical Investigation of Convective Heat Transfer in a Gas Turbine Can Combustor

Experiments and numerical computations are performed to investigate the convective heat transfer characteristics of a gas turbine can combustor under cold flow conditions in a Reynolds number range between 50,000 and 500,000 with a characteristic swirl number of 0.7. It is observed that the flow field in the combustor is characterized by an expanding swirling flow, which impinges on the liner wall close to the inlet of the combustor. The impinging shear layer is responsible for the peak location of heat transfer augmentation. It is observed that as Reynolds number increases from 50,000 to 500,000, the peak heat transfer augmentation ratio (compared with fully developed pipe flow) reduces from 10.5 to 2.75. This is attributed to the reduction in normalized turbulent kinetic energy in the impinging shear layer, which is strongly dependent on the swirl number that remains constant at 0.7 with Reynolds number. Additionally, the peak location does not change with Reynolds number since the flow structure in the combustor is also a function of the swirl number. The size of the corner recirculation zone near the combustor liner remains the same for all Reynolds numbers and hence the location of shear layer impingement and peak augmentation does not change.

Effect of Temperature Ratio on Jet Array Impingement Heat Transfer

This paper consider the effects of temperature ratio on the heat transfer from an array of jets impinging on a flat plate. At a constant Reynolds number of 18,000 and a constant Mach number of 0.2, different ratios of target plate temperature to jet temperature are employed. The spacing between holes in the streamwise direction X is 8D, and the spanwise spacing between holes in a given streamwise row Y is also 8D. The target plate is located 3D away from the impingement hole exits. Experimental results show that local, line-averaged, and spatially averaged Nusselt numbers decrease as the T wa /T j temperature ratio increases. This is believed to be due to the effects of temperature-dependent fluid properties, as they affect local and global turbulent transport in the flow field created by the array of impinging jets. The effect of temperature ratio on crossflow-to-jet mass velocity ratio and discharge coefficients is also examined.

Effects of Jet-to-Target Plate Distance and Reynolds Number on Jet Array Impingement Heat Transfer

Data which illustrate the effects of jet-to-target plate distance and Reynolds number on the heat transfer from an array of jets impinging on a flat plate are presented. Considered are Reynolds numbers Rej ranging from 8200 to 52,000 with isentropic jet Mach numbers of approximately 0.1 to 0.2. Jet-to-target plate distances Z of 1.5D, 3.0D, 5.0D, and 8.0D are employed, where D is the impingement hole diameter. Streamwise and spanwise hole spacings are 8D. Local and spatially-averaged Nusselt numbers show strong dependence on the impingement jet Reynolds number for all situations examined. Experimental results also illustrate the dependence of local Nusselt numbers on normalized jet-to-target plate distance, especially for smaller values of this quantity. The observed variations are partially due to accumulating cross-flows produced as the jets advect downstream, as well as the interactions of the vortex structures, which initially form around the jets and then impact and interact as they advect away from stagnation points along the impingement target surface. The highest spatially-averaged Nusselt numbers are present for Z/D = 3.0 for Rej of 8200, 20,900, and 30,000. When Rej = 52,000, spatially-averaged Nusselt numbers increase as Z/D decreases, with the highest value present at Z/D = 1.5.

Mach Number, Reynolds Number, Jet Spacing Variations: Full Array of Impinging Jets

Presented are data that illustrate the effects of Mach number, Reynolds number, and hole spacing on surface Nusselt numbers produced by an array of jets impinging on a flat plate. Considered are Reynolds numbers ranging from 17,300 to 60,000 and Mach numbers from 0.1 to 0.45. Impingement hole spacings are 5D, 8D, and 12D in the streamwise and spanwise directions. Local spatially resolved and spatially averaged Nusselt numbers, measured using infrared thermography and energy balance techniques, show strong dependence on the impingement jet Reynolds number for each situation as the jet Mach number is maintained constant. Nusselt numbers show negligible variations between Ma = 0.1 and 0.2; however, data taken at Mach numbers greater than 0.2 (as the Reynolds number is held constant) show that Mach number has a significant impact on local and spatially averaged Nusselt numbers. This Mach number dependence changes with hole spacing, with greater Nusselt number increases with the less dense impingement arrays. These variations are described using new correlations, which account for the effects of Mach number for all three impingement hole spacings.

High Rotation Number Effect on Heat Transfer in a Triangular Channel With 45 deg, Inverted 45 deg, and 90 deg Ribs

Heat transfer and pressure drop have been experimentally investigated in an equilateral triangular channel (D h =1.83 cm), which can be used to simulate the internal cooling passage near the leading edge of a gas turbine blade. Three different rib configurations (45 deg, inverted 45 deg, and 90 deg) were tested at four different Reynolds numbers (10,000-40,000), each with five different rotational speeds (0―400 rpm). The rib pitch-to-height (Ple) ratio is 8 and the height-to-hydraulic diameter (e/D h ) ratio is 0.087 for every rib configuration. The rotation number and buoyancy parameter achieved in this study were 0―0.58 and 0―2.3, respectively. Both the rotation number and buoyancy parameter have been correlated with predict the rotational heat transfer in the ribbed equilateral triangular channel. For the stationary condition, staggered 45 deg angled ribs show the highest heat transfer enhancement. However, staggered 45 deg angled ribs and 90 deg ribs have the higher comparable heat transfer enhancement at rotating condition near the blade leading edge region.