scholarly journals An Experimental Investigation on the Flow Characteristics Over Dimple Arrays Pertinent to Internal Cooling of Turbine Blades

2014 ◽  
Author(s):  
Wenwu Zhou ◽  
Hui Hu ◽  
Yu Rao
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Flat Surface ◽  
Reynolds Shear Stress ◽  
Turbine Blades ◽  
Flow Characteristics ◽  
Internal Cooling ◽  
Transfer Enhancement

Due to the dimple’s unique characteristics of comparatively low pressure loss penalty and good heat transfer enhancement performance, dimple provides a very desirable alternative internal cooling technique for gas turbine blades. In the present study, an experimental investigation was conducted to quantify the flow characteristics over staggered dimple arrays and to examine the vortex structures inside the dimples. In addition to the surface pressure measurements, a high-resolution digital Particle Image Velocimetry (PIV) system was also utilized to achieve detailed flow field measurements to quantify the characteristics of the turbulent channel flow over the dimple arrays in terms of the ensemble-averaged velocity, Reynolds shear stress and turbulence kinetic energy (TKE) distributions. The experimental measurement results show that the friction factor of the dimpled surface is much higher than that of a flat surface. The measured pressure distribution within a dimple reveals clearly that flow separation and attachment would occur inside each dimple. In comparison with those of a conventional channel flow with flat surface, the channel flow over the dimpled arrays was found to have much stronger Reynolds stress and higher TKE level. Such unique flow characteristics are believed to be the reasons why a dimpled surface would have a better heat transfer enhancement performance for internal cooling of turbine blades as reported in those previous studies.

Rib Spacing Effect on Heat Transfer and Pressure Loss in a Rotating Two-Pass Rectangular Channel (AR=1:2) With 45-Degree Angled Ribs

2006 ◽  
Author(s):  
Yao-Hsien Liu ◽  
Lesley M. Wright ◽  
Wen-Lung Fu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Spacing Effect ◽  
Turbine Blades ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Smooth Channel

Rib turbulators are commonly used to enhance the heat transfer within internal cooling passages of advanced gas turbine blades. Many factors affect the thermal performance of a cooling channel with ribs. This study experimentally investigates the effect of rib spacing on the heat transfer enhancement, pressure penalty, and thus the overall thermal performance in both rotating and non-rotating rectangular, cooling channels. In the 1:2 rectangular channels, 45° angled ribs are placed on the leading and trailing surfaces. The pitch of the ribs varies, so rib pitch-to-height (P/e) ratios of 10, 7.5, 5, and 3 are considered. Square ribs with a 1.59 mm × 1.59 mm cross-section are used for all spacings, so the height-to-hydraulic diameter (e/Dh) ratio remains constant at 0.094. With a constant rotational speed of 550 rpm and the Reynolds number ranging from 5000 to 40000, the rotation number in turn varies from 0.2 to 0.02. Because the skewed turbulators induce secondary flow along the length of the rib, the very close rib spacing of P/e = 3, has the best thermal performance in both rotating and non-rotating channels. This close spacing yields the greatest heat transfer enhancement, while the P/e = 5 spacing has the greatest pressure penalty. In addition, the effect of rotation is more pronounced in the channel with the rib spacing of 3. As more ribs are added, the channel is approaching a smooth channel, and the strength of the rotation induced vortices increases.

scholarly journals Internal Cooling Using Novel Swirl Enhancement Strategies in a Slot Shaped Single Pass Channel

2010 ◽  
Author(s):  
Del Segura ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Turbine Blades ◽  
Main Channel ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Mean Velocity ◽  
Performance Factors ◽  
Air Temperatures ◽  
Rectangular Channels

Heat transfer results for a given slot shaped channel with a 3:1 aspect ratio are presented using various methods to enhance swirl in the channel including helical shaped-trip-strips and swirl-jets issuing from the side walls. Four different configurations of the swirl jets and one configuration of the helical trip strips were studied. The Reynolds numbers investigated range from 10,000 to 50,000 and are based on the mean velocity of the fluid at the channel inlet, or when swirl-jets are used, the equivalent mass flow rates at the exit of the main channel. Independently these heat transfer enhancement strategies have proven to be effective in either round channels, in the case of swirl jets and helical protrusions, or rectangular channels, in the case of trip strips. A transient technique combined with Duhamel’s superposition theorem was used to obtain the heat transfer coefficient distributions. Narrow-band liquid crystals were used to map the transient surface temperatures and were combined with thermocouples that measured the bulk-air temperatures along the flow path in the main channel. The results for the tests reported in this paper show mean heat transfer enhancement values (Nu/Nuo) greater than 4.5 and low normalized friction factors. Thermal performance factors ranged from 1.1–3.3 for the various configurations studied. These results show significant improvements over other types of heat transfer enhancement methods currently used in the mid-span section of turbine blades.

Heat Transfer Enhancement in Channel Flow Using an Inclined Square Cylinder

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Dong-Hyeog Yoon ◽  
Kyung-Soo Yang ◽  
Choon-Bum Choi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Large Scale ◽  
Channel Wall ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Vortex Generator ◽  
Square Cylinder ◽  
Transfer Enhancement

Heat transfer enhancement in channel flow by using an inclined vortex generator has been numerically investigated. A square cylinder is located on the centerline of laminar channel flow, which is subject to a constant heat flux on the lower channel wall. As the cylinder is inclined with some angle of attack with respect to the main flow direction, flow characteristics change downstream of the cylinder, and significantly affect heat transfer on the channel wall. A parametric study has been conducted to identify the cause, and to possibly find the optimal inclination angle. It turns out that the increased periodic fluctuation of the vertical velocity component in the vicinity of the channel walls is responsible for the heat transfer enhancement. The large fluctuation is believed to be induced by the large-scale vortices shed from the inclined square cylinder, as well as by the secondary vortices formed near the channel walls.

Swirl-Enhanced Internal Cooling of Turbine Blades: Part 1—Radial Flow Entry

2011 ◽  
Author(s):  
Del Segura ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Turbine Blades ◽  
Main Channel ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Mean Velocity ◽  
Performance Factors ◽  
Air Temperatures ◽  
The Mean

Heat transfer results for a given slot shaped channel with a 3:1 aspect ratio and jets issuing from side walls are presented. Two different jet configurations are used as a means to enhance turbulence in the main flow stream. The Reynolds numbers investigated range from 10,000 to 50,000 and are based on the mean velocity of the fluid at the channel inlet for the slot shaped channel without enhancement, or when swirl-jets are used, the equivalent mass flow rates at the exit of the main channel. Blowing Ratios, defined as the mean side jet velocity verses the mean main channel velocity, ranged from 8.6 to 30.2. This heat transfer enhancement strategy has proven to be effective in round channels. A transient technique combined with Duhamel’s superposition theorem was used to obtain the heat transfer coefficient distributions. Narrow-band liquid crystals were used to map the transient surface temperatures and were combined with thermocouples that measured the center-line air temperatures along the flow path in the main channel. The results of the passage with jet enhancements were compared to the smooth slot channel, without any type of heat transfer enhancements. The tests results reported in this paper show mean heat transfer enhancement values (Nu/Nuo smooth) greater than 4.2 and low normalized friction factors. Thermal performance factors (OTP) ranged from 1.55–3.69 for the various configurations studied. These results show significant improvements over other types of heat transfer enhancement methods currently used in the mid-span section of turbine blades.

Effect of Rib Turbulators in the First Pass on Heat Transfer Distributions in a Two-Pass Channel Connected by Two Rows of Holes

2001 ◽  
Author(s):  
Srinath V. Ekkad ◽  
David Kontrovitz ◽  
Hasan Nasir ◽  
Gautam Pamula ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Serpentine Channel ◽  
First Pass ◽  
Rib Turbulators

This paper is a continued study of new internal channel cooling designs for modern gas turbine blades. In previous studies, the enhanced cooling in the second pass of a serpentine channel was achieved by a combination of impingement and crossflow-induced swirl. A holed or slotted divider wall replaced the 180° U-turn connecting the two legs of the serpentine channel. Flow from one coolant passage to the adjoining coolant passage was achieved through a series of straight and angled holes and a two-dimensional slot placed along the dividing wall. In this study, the focus is to enhance the heat transfer in the first pass of the two-pass channel using traditional rib turbulators. The effect of ribs in the first pass on the overall second pass heat transfer enhancement is compared to channels with no rib turbulators. Heat transfer distributions are compared for channels with and without ribs for three-channel flow Reynolds numbers ranging between 1.0×104 − 5.0×104. Results show that the presence of the ribs in the first pass reduces the heat transfer coefficients slightly in the second pass compared to the no-ribs channels. However, the first pass heat transfer is significantly enhanced over the case without ribs. In effect, the overall heat transfer enhancement for the combined two passes is significantly enhanced. Three different rib configurations, 90° ribs, 60° angled forward facing towards divider wall, and 60° angled backward facing away from divider wall, are studied for all Reynolds numbers and divider wall geometries. The presence of ribs in the first pass does not only decrease the enhanced heat transfer in the second pass but also provides higher heat transfer enhancement in the first pass resulting in an increase in overall heat transfer enhancement for the entire two-pass channel.

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