The effect of single-sided ribs on heat transfer and pressure drop within a trailing edge internal channel of a gas turbine blade

2021 ◽  
pp. 1-43
Author(s):  
Suhyun Kim ◽  
Seungwon Suh ◽  
Seungchan Baek ◽  
Wontae Hwang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Secondary Flow ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Sharp Corner ◽  
Trailing Edge ◽  
Edge Channel ◽  
Ribbed Channel

Abstract Convective cooling in a gas turbine blade internal trailing edge channel is often insufficient at the sharp trailing edge. This study examines convective heat transfer and pressure drop within a simplified trailing edge channel. The internal passage has been modeled as a right triangular channel with a 9° angle sharp corner. Smooth baseline and ribbed copper plates were heated from underneath via a uniform heat flux heater and examined via infrared thermography. Non-uniformity in the heat flux due to conduction is corrected by a RANS conjugate heat transfer calculation, which was validated by the mean velocity, friction factor, and temperature fields from experiments and LES simulations. Nusselt number distributions illustrate that surface heat transfer is increased considerably with ribs, and coupled with the vortices in the flow. Heat transfer at the sharp corner is increased by more than twofold due to ribs placed at the center of the channel, due to secondary flow. The present partially ribbed channel utilizes secondary flow toward the corner, and is presumed to have better thermal performance than a fully ribbed channel. Thus, it is important to set the appropriate rib length within the channel.

scholarly journals Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Waseem Siddique ◽  
Lamyaa El-Gabry ◽  
Igor V. Shevchuk ◽  
Torsten H. Fransson
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Secondary Flow ◽  
Gas Turbine ◽  
Bottom Surface ◽  
Trailing Edge ◽  
Enhancement Of Heat Transfer ◽  
Trapezoidal Channel ◽  
Ribbed Channel ◽  
Edge Surface

High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. In particular, the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer; therefore, for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at the trailing edge surface in-line with the ribs at the bottom surface, and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-ɛ model, realizable k-ɛ model, the RNG k-ω model, low-Re k-ω model, and SST k-ω models are compared, whereas for ribbed channel, low-Re k-ɛ model and SST k-ω models are compared. The results show that the low-Re k-ɛ model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by −17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for the ribbed trailing edge only was found about 8% better than other configurations.

Influence of Ribs on Internal Heat Transfer and Pressure Drop in a Turbine Blade Trailing Edge Channel

2020 ◽  
Author(s):  
Suhyun Kim ◽  
Seungwon Suh ◽  
Seungchan Baek ◽  
Wontae Hwang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Convective Heat Transfer ◽  
Friction Factor ◽  
Turbine Blade ◽  
Convective Heat ◽  
Sharp Corner ◽  
Trailing Edge

Abstract Convective cooling inside the internal passage of a turbine blade trailing edge is often insufficient at the sharp corner, when cutback slot cooling is not present. This study investigates the convective heat transfer and pressure drop in a simplified trailing edge internal channel. The internal passage has been modeled as a right triangular channel with a 9° angle sharp corner. Heated baseline (with no internal features) and ribbed copper plates have been examined via infrared thermography. A uniform heat flux heater is installed beneath the plates, and non-uniformities in the heat flux due to conduction is corrected by a RANS conjugate heat transfer calculation. The numerical simulations were validated beforehand by experimental results of mean velocity, friction factor, and temperature fields. Nusselt number distributions show that convective heat transfer is significantly enhanced with ribs, and closely coupled with the vortical flow structure. Heat transfer at the corner is increased by more than a factor of two with ribs, due to secondary flow towards the corner. Although the pressure loss and friction increase slightly, the overall thermal performance, represented by the average Nusselt number with respect to the friction factor, increases by a factor of two with the ribs.

scholarly journals Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge

2011 ◽  
Author(s):  
Waseem Siddique ◽  
Igor V. Shevchuk ◽  
Lamyaa A. El-Gabry ◽  
Torsten H. Fransson
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Secondary Flow ◽  
Gas Turbine ◽  
Bottom Surface ◽  
Trailing Edge ◽  
Enhancement Of Heat Transfer ◽  
Trapezoidal Channel ◽  
Ribbed Channel ◽  
Edge Surface

High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. Especially the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer therefore for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at trailing edge surface in-line with the ribs at bottom surface and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-ε model, realizable k-ε model, the RNG k-ω model, low-Re k-ω model and SST k-ω models are compared, whereas for ribbed channel low-Re k-ε model and SST k-ω models are compared. The results show that the low-Re k-ε model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by −17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for ribbed trailing edge only, was found about 8% better than other configurations.

Experimental Study on Flow Behavior and Heat Transfer Enhancement with Distinct Dimpled Gas Turbine Blade Internal Cooling Channel

2021 ◽  
pp. 1-28
Author(s):  
Farah Nazifa Nourin ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Thermal Performance ◽  
Diameter Ratio ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Enhancement

Abstract The study presents the investigation on heat transfer distribution along a gas turbine blade internal cooling channel. Six different cases were considered in this study, using the smooth surface channel as a baseline. Three different dimples depth-to-diameter ratios with 0.1, 0.25, and 0.50 were considered. Different combinations of partial spherical and leaf dimples were also studied with the Reynolds numbers of 6,000, 20,000, 30,000, 40,000, and 50,000. In addition to the experimental investigation, the numerical study was conducted using Large Eddy Simulation (LES) to validate the data. It was found that the highest depth-to-diameter ratio showed the highest heat transfer rate. However, there is a penalty for increased pressure drop. The highest pressure drop affects the overall thermal performance of the cooling channel. The results showed that the leaf dimpled surface is the best cooling channel based on the highest Reynolds number's heat transfer enhancement and friction factor. However, at the lowest Reynolds number, partial spherical dimples with a 0.25 depth to diameter ratio showed the highest thermal performance.

Heat Transfer in a Vane Trailing Edge Passage With Conical Pins and Pin-Turbulator Integrated Configurations

2014 ◽  
Author(s):  
J. Kruekels ◽  
S. Naik ◽  
A. Lerch ◽  
A. Sedlov
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Internal Heat ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Heat Transfer Coefficients ◽  
Trailing Edges ◽  
Converging Channel ◽  
Internal Heat Transfer

The trailing edge sections of gas turbine vanes and blades are generally subjected to extremely high heat loads due to the combined effects of high external accelerating Mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfills the mechanical integrity of the parts, highly efficient cooling of the trailing edges is required without increasing the coolant consumption, as the latter has a detrimental effect on the overall gas turbine performance. In this paper the characteristics of the heat transfer and pressure drop of two novel integrated pin bank configurations were investigated. These include a pin bank with conical pins and a pin bank consisting of cylindrical pins and intersecting broken turbulators. As baseline case, a pin bank with cylindrical pins was studied as well. All investigations were done in a converging channel in order to be consistent with the real part. The heat transfer and pressure drop of all the pin banks were investigated initially with the use of numerical predictions and subsequently in a scaled experimental wind tunnel. The experimental study was conducted for a range of operational Reynolds numbers. The TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients in scaled Perspex models representing the various pin bank configurations. Pressure taps were located at several positions within the test sections. Both local and average heat transfer coefficients and pressure loss coefficients were determined. The measured and predicted results showed that the local internal heat transfer coefficient increases in the flow direction. This was due to the flow acceleration in the converging channel. Furthermore, both the broken ribs and the conical pin banks resulted in higher heat transfer coefficients compared with the baseline cylindrical pins. The conical pins produced the highest average internal heat transfer coefficients in contrast to the pins with the broken ribs, though this was also associated with a higher pressure drop.

Effect of Rotation on Heat Transfer in AR = 2:1 and AR = 4:1 Channels Connected by a Series of Crossover Jets

2021 ◽  
pp. 1-19
Author(s):  
Srivatsan Madhavan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Flow Direction ◽  
Gas Turbine Blade ◽  
Trailing Edge ◽  
Cooling Flow ◽  
Liquid Crystal Thermography ◽  
Pin Fins ◽  
Rib Turbulators

Abstract Detailed heat transfer measurements using transient liquid crystal thermography were performed on a novel cooling design covering the mid-chord and trailing edge region of a typical gas turbine blade under rotation. The test section comprised of two channels with aspect ratio (AR) of 2:1 and 4:1, where the coolant was fed into the AR = 2:1 channel. Rib turbulators with a pitch-to-rib height ratio (p/e) of 10 and rib height-to-channel hydraulic diameter ratio (e/Dh) of 0.075 were placed in the AR = 2:1 channel at 60° relative to flow direction. The coolant after entering this section was routed to the AR = 4:1 section through a set of crossover jets. The 4:1 section had a realistic trapezoidal shape that mimics the trailing edge of an actual gas turbine blade. The pin fins were arranged in a staggered array with a center-to-center spacing of 2.5 times pin diameter. The trailing edge section consisted of radial and cutback exit holes for flow exit. Experiments were performed for Reynolds number of 20,000 at Rotation numbers (Ro) of 0, 0.1 and 0.14. The channel averaged heat transfer coefficient on trailing side was ~28% (AR = 2:1) and ~7.6% (AR = 4:1) higher than the leading side for Ro = 0.1. It is shown that the combination of crossover jets and pin-fins can be an effective method for cooling wedge shaped trailing edge channels over axial cooling flow designs.

Numerical Studies on Effect of Channel Orientation in a Rotating Smooth Wedge-Shaped Cooling Channel

2014 ◽  
Author(s):  
Balamurugan Srinivasan ◽  
Anand Dhamarla ◽  
Chandiran Jayamurugan ◽  
Amarnath Balu Rajan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Cooling Channel ◽  
Transfer Enhancement ◽  
Trailing Edge ◽  
Pin Fins ◽  
Channel Orientation ◽  
The Heat Transfer Coefficient

The increasing demands of better efficiency of modern advanced gas turbine require higher turbine inlet temperatures, which gives great challenges to turbine blade designers. However, the temperature limits of turbine blade material are not high enough to ensure its survival in such incredible operating temperature. Hence, both internal and external cooling approaches have been developed and widely used in today’s turbine blade. To internal cooling problems, a variety of cooling enhancement approaches, such as impingement and turbulators, are employed in order to meet the different needs in leading, middle and trailing region. One of the most critical parts in turbine blade is trailing edge where it is hard to cool due to its narrow shape. Pin-fins are widely used to cool the trailing edge of rotor and stator blades of gas turbine engine. Pin-fins offer significant heat transfer enhancement, they are relatively easy to fabricate and offer structural support to the hollow trailing edge region. The flow physics in a pin-fin roughened channel is very complicated and three-dimensional. In this work, we have studied the effect of channel orientation on heat transfer in a rotating wedge-shaped cooling channel using numerical methods. Qiu [1] studied experimentally heat transfer effects of 5 different angles of wedge shaped channel orientation for the inlet Reynolds number (5100 to 21000) and rotational speed (zero to 1000 rpm), which results in the inlet Rotation number variation from 0 to 0.68. They observed that compared to the non-rotating condition, there is about 35% overall heat transfer enhancement under highest rotation number. The above said results are validated using current studies with Computational Fluid Dynamics (CFD) revealed that rotation increases significantly the heat transfer coefficient on the trailing surface and reduces the heat transfer coefficient on the leading surface. This is due to the higher velocities associated with the converging geometry near trailing surface.

Numerical Investigation on Flow and Heat Transfer Characteristics of Steam and Mist/Steam in Internal Cooling Channels With Different Rib Angles

2016 ◽  
Author(s):  
Junxiong Zeng ◽  
Tieyu Gao ◽  
Jun Li ◽  
Jiangnan Zhu ◽  
Jiyou Fei
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Gas Turbine ◽  
Heat Transfer Performance ◽  
Secondary Flows ◽  
Heat Transfer Characteristics ◽  
Cooling Channels ◽  
Ribbed Channel ◽  
Steam Cooling ◽  
Cooling Technology

In order to further increase the gas turbine efficiency by increasing the turbine inlet temperature, an advanced cooling technology needs to be developed. Recently, mist /steam (air) cooling is considered as a promising technology to effectively cool the hot components such as gas turbine vanes and blades. A series of experimental investigations and numerical simulations conducted in the past proved the feasibility and superiority of mist cooling technology in elevated gas turbine working condition. The aim of this study is to numerically analyze the secondary flow structure and the influence of secondary flow distribution on heat transfer in steam and mist/steam cooling channels with different rib angles by using vortex core interaction. In addition, the heat transfer characteristics of steam and mist/steam in gas turbine cooling channels with rib angles of 30°, 45°, 60°, 90°, duct aspect ratio 2:1, Reynolds number ranging from 10000 to 60000 and mist ratio increasing from 2% to 8% are also investigated. The commercial software ANSYS CFX 14.5 is used to solve the 3-D steady Reynolds-averaged Navier–Stokes equations with a SST turbulent model. The numerical results of Nusselt number (Nu) distribution along the centerline of each channel with steam-only are validated with the experimental values. Numerical results indicate that the predicted results are in good agreement with the experimental data. The distribution and strength of longitudinal secondary flows in 30°, 45°, 60° ribbed channels and transverse secondary flows in 90° ribbed channel have a great influence on the distribution of Nusselt number. The averaged Nu in 30°, 45°, 60° ribbed channels is higher than that in 90° ribbed channel due to longitudinal secondary flow having a better heat transfer performance than transverse secondary flow. The decrease of averaged Nu between two neighbored ribs along inclined ribs is mainly induced by the decreased strength of longitudinal secondary flow along the same direction in 30°, 45°, 60°ribbed channels. The averaged Nu of mist/steam with 5% mist injection in the four channels increases by 97.98%–151.9% compared with steam at Re=60000. Furthermore, the averaged Nu increases by about 11.08% to 213.6% compared with steam, when the mist ratio increases from 2% to 8%. The 60°ribbed channel achieves the best heat transfer performance in mist/steam cooling channels.

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