Performance Evaluation of a Modified Cross Section Grooved Channel as Turbulence Promoter in Internal Cooling Channel of a Gas Turbine Blade

2015 ◽  
Author(s):  
Krishnendu Saha ◽  
Deoras Prabhudharwadkar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Cross Section ◽  
Channel Wall ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Ribbed Channel ◽  
Baseline Case ◽  
Mainstream Flow

Internal cooling channel in gas turbine blades use ribs as turbulence promoter to increase local turbulence and improve heat transfer from hot wall to coolant air flowing through the internal cooling channels. The ribs protrude into the flow and result in a significant pressure drop of the coolant air. Indentations like grooves in the cooling channel wall can also be used as turbulence promoters to enhance local heat transfer and as they do not protrude into the mainstream flow, the pressure drop penalty could be much lesser than a conventional ribbed channel. A numerical study is conducted under stationary condition on a square cross section channel representing an internal cooling channel of a turbine airfoil. Some standard and modified cross sections of grooved channel are used as turbulence promoters with a goal to enhance heat transfer from the internal cooling channel wall with minimal pressure drop. The steady state solution is based on using the Reynolds Averaged Navier-Stokes (RANS) equation and k-omega-SST turbulence model. Numerical calculations are done at four Reynolds numbers (Re=15000, 30000, 68000 and 88000) based on fluid properties at the inlet of the internal cooling channel. The grooves are placed on two opposite sides of the square cross section channel and other two walls are smooth walls without any turbulence promoters. A hemispherical cross section continuous groove which is placed perpendicular to the mainstream flow direction is taken as baseline case and a teardrop shaped groove is used to compare the performance difference between the two groove cross section. A broken shaped angled groove configuration with the teardrop cross section groove is also investigated to find the relative performance improvement with the baseline case. Performance comparison with standard 90° rib geometry is done to understand the overall effectiveness of the grooved geometries with respect to common standard in gas turbine blade internal cooling. The straight teardrop cross section groove improves the heat transfer values compared to the hemispherical cross section groove by 8–12% and the broken angled teardrop groove case improves heat transfer by 11–14% compared to the hemispherical cross section groove case. The pressure drop produced by all the groove geometries is about the same. It is seen that the broken angled groove can produce the same heat transfer enhancement compared to a 90° ribbed channel but the pressure drop is more than 3 times lesser compared to the ribbed case. Considering the heat transfer and pressure drop, an increase in thermal performance factor of 37–41% is seen for the angled grooved case compared to the 90° ribbed geometry.

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 Rotating, Blade-Shaped, Two-Pass Cooling Channel With a Variable Aspect Ratio

2021 ◽  
Author(s):  
I-Lun Chen ◽  
Izzet Sahin ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Gas Turbine ◽  
Cross Section ◽  
Pressure Loss ◽  
Planar Geometry ◽  
Internal Cooling ◽  
Cooling Channel ◽  
First Passage ◽  
Rotating Blade

Abstract This study features a rotating, blade-shaped, two-pass cooling channel with a variable aspect ratio. Internal cooling passages of modern gas turbine blades closely follow the shape and contour of the airfoils. Therefore, the cross-section and the orientation with respect to rotation varies for each cooling channel. The effect of passage orientation on the heat transfer and pressure loss is investigated by comparing to a planar channel design with a similar geometry. Following the blade cross-section, the first pass of the serpentine channel is angled at 50° from the direction of rotation while the second pass has an orientation angle of 105°. The coolant flows radially outward in the first passage with an aspect ratio (AR) = 4:1. After a 180-degree tip turn, the coolant travels radially inward into the second passage with AR = 2:1. The copper plate method is applied to obtain the regionally-averaged heat transfer coefficients on all the interior walls of the cooling channel. In addition to the smooth surface case, 45° angled ribs with a profiled cross section are also placed on the leading and trailing surfaces in both the passages. The ribs are placed such that P/e = 10 and e/H = 0.16. The Reynolds number varies from 10,000 to 45,000 in the first passage and 16,000 to 73,000 in the second passage. The rotational speed ranges from 0 to 400 rpm, which corresponds to maximum rotation numbers of 0.38 and 0.15 in the first and second passes, respectively. The blade-shaped feature affects the heat transfer and pressure loss in the cooling channels. In the second passage, the heat transfer on the outer wall and trailing surface is higher than the inner wall and leading surface due to flow impingement and the swirling motion induced by the blade-shaped tip turn. The rotational effect on the heat transfer and pressure loss is lower in the blade-shaped design than the planar design due to the feature of angled rotation. The tip wall heat transfer is significantly enhanced by rotation in this study. The overall heat transfer and pressure loss in this study is higher than the planar geometry due to the blade-shaped feature. The heat transfer and pressure loss characteristics from this study provide important information for the gas turbine blade internal cooling designs.

Rib Cross Section Optimization of a Ribbed Turbine Internal Cooling Channel With Experimental Validation

2017 ◽  
Author(s):  
Firat Kiyici ◽  
Sefa Yilmazturk ◽  
Kahraman Coban ◽  
Ercan Arican ◽  
Emiliano Costa ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Cross Section ◽  
Bulk Temperature ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Internal Channel ◽  
Turbine Inlet ◽  
Cooling Passage

Due to the recent developments of the engine industry, turbine internal channel cooling is a need. In fact, in order to supply more power efficiently, the fluid temperature at turbine inlet approaches to 2000 K when common turbine materials cannot resist temperature values higher than 1500 K. The crucial point is that the engine cycle efficiency and thrust highly depend on the turbine inlet temperature and, so, such a thermal problem needs to be overcome by cooling. Coolant air of the internal channel cooling systems is mostly taken from valuable compressor bleed that makes it to circulate through the serpentine internal passages. The coolant air flow is commonly fully turbulent, incompressible and with 3D characteristics because of the complex shape of the cooling passage. Considering this latter aspect, the pressure drop also plays a relevant role because, in order to minimize the cooling mass flow, it needs to be reduced. In this study, rib cross-section shape optimization of a ribbed internal cooling channel is conducted to assess the trade-off between two conflicting objectives: heat transfer performance and pressure drop. For this purpose, a novel mesh morphing based optimization tool is developed which uses radial basis functions (RBF) for morphing and meta-model assisted evolutionary algorithms (EA) for optimization. Experimental tests characterized by Reynolds number of 20000 are performed to validate such an optimization tool. The local Nusselt number is calculated using hydraulic diameter of channel and air thermal conductivity corresponding to bulk temperature. The cooling effectiveness of the channel is quantified using the ratio of the Nusselt number of the ribbed case to the Nusselt number of the smooth case. With the gained optimized geometry, the heat transfer shows better results than initial case with a pressure loss improvement of 8%.

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.

Topology Optimization of Serpentine Channels for Minimization of Pressure Loss and Maximization of Heat Transfer Performance As Applied for Additive Manufacturing

2019 ◽  
Author(s):  
Shinjan Ghosh ◽  
Jayanta S. Kapat
Keyword(s):  
Heat Transfer ◽  
Topology Optimization ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Blade Cooling

Abstract Gas Turbine blade cooling is an important topic of research, as a high turbine inlet temperature (TIT) essentially means an increase in efficiency of gas turbine cycles. Internal cooling channels in gas turbine blades are key to the cooling and prevention of thermal failure of the material. Serpentine channels are a common feature in internal blade cooling. Optimization methods are often employed in the design of blade internal cooling channels to improve heat-transfer and reduce pressure drop. Topology optimization uses a variable porosity approach to manipulate flow geometries by adding or removing material. Such a method has been employed in the current work to modify the geometric configuration of a serpentine channel to improve total heat transferred and reduce the pressure drop. An in-house OpenFOAM solver has been used to create non-traditional geometries from two generic designs. Geometry-1 is a 2-D serpentine passage with an inlet and 4 bleeding holes as outlets for ejection into the trailing edge. Geometry-2 is a 3-D serpentine passage with an aspect ratio of 3:1 and consists of two 180-degree bends. The inlet velocity for both the geometries was used as 20 m/s. The governing equations employ a “Brinkman porosity parameter” to account for the porous cells in the flow domain. Results have shown a change in shape of the channel walls to enhance heat-transfer in the passage. Additive manufacturing can be employed to make such unconventional shapes.

Trailing Edge Cooling of Gas Turbine Airfoil Using Blockages With Straight and Inclined Holes

2014 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Pressure Loss ◽  
Heat Transfer Performance ◽  
Experimental Studies ◽  
Internal Cooling ◽  
Transfer Performance ◽  
Trailing Edge ◽  
High Heat Transfer ◽  
Baseline Case

This paper describes the detailed experimental studies of heat transfer enhancement and pressure loss characteristics internal cooling passages using single, double and triple blockages equipped with straight and inclined holes. The blockage consist of 7 holes with the diameter, D = 6.35mm, which is 0.5 of the height of the channel. Three different hole inclination angles ranging from 0°, 15° and 30° from the horizontal plane are explored. The case with straight holes (0°) is considered as baseline case, while the cases with inclined holes are introduced to enhance heat transfer performance. The transient liquid crystal technique is employed to deduce the heat transfer coefficient on the internal cooling channel, while the pressure loss of the entire channel is measured using pressure taps connected to the digital manometer. Numerical analysis is later performed using ANSYS CFX, based on the shear stress turbulence (SST) model to provide detailed insights about the flow field in the channel, which explains the heat transfer phenomena caused by varying the hole inclination angle. The heat transfer performance of the blockages is higher than conventional configuration using vortex generators, i.e., pin-fins by approximately two folds, while accompanied by much higher pressure loss. The proposed inclined holes array exhibits more effective impingement effects resulted in a substantial cooling performance compared to the baseline case by approximately 50%. This design can be applicable to the trailing edge of gas turbine airfoils, which can provide high heat transfer rate and pressure loss from repeated significant area contractions.

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.

Numerical Simulation of Two Pass Gas Turbine Blade Internal Cooling Channels With 90 Degree Varying Height Ribs

2012 ◽  
Author(s):  
Sourabh Kumar ◽  
R. S. Amano
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Gas Turbine ◽  
Thermal Stresses ◽  
Turbine Blades ◽  
Simulation Software ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Ribbed Channel ◽  
Smooth Channel

Improvement in thermal efficiency of gas turbine can be obtained by operating it at high inlet temperatures. In addition to improving the performance, the cons of high inlet temperature is high thermal stresses on the turbine blades. To improve life and performance of the blade, improved cooling technologies are desired. The main objective of this paper is to perform computational analysis of the ribs with varying height and compare this with 90 degree ribbed channel and smooth channels. The numerical analysis is carried out using ANSYS-Fluent, a flow modeling simulation software. The flow is assumed to be steady state and flow turbulence is modeled using the k-ε with Standard Wall Functions. Local heat transfer and friction loss in a square duct roughened with 90 degree ribs with varying height is investigated for different Reynolds number. The pitch of the rib is considered to be 10 times the height of rib which is 0.0635 m. The square cross section of the channel is .0508x .0508 m2. The pitch of rib to rib height ratio varies from 10 to 20 at the center of the channel. There is a rib considered at the turn section as well. The numerical simulation produced higher heat transfer for the varying height ribs as compared to 90 degree ribbed channel and smooth channel.

Numerical Investigation on the Modified Bend Geometry of a Rotating Multipass Internal Cooling Passage in a Gas Turbine Blade

2018 ◽  
Vol 10 (6) ◽  
Author(s):  
Naris Pattanaprates ◽  
Ekachai Juntasaro ◽  
Varangrat Juntasaro
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Internal Cooling ◽  
Gas Turbine Blade ◽  
Reduced Pressure ◽  
Improve Heat Transfer ◽  
Cooling Passage ◽  
Internal Cooling Passage

Abstract The present work is aimed to investigate whether the modification to the bend geometry of a multipass internal cooling passage in a gas turbine blade can enhance heat transfer and reduce pressure drop. The two-pass channel and the four-pass channel are modified at the bend from the U shape to the bulb and bow shape. The first objective of the work is to investigate whether the modified design will still improve heat transfer with reduced pressure drop in a four-pass channel as in the case of a two-pass channel. It is found out that, unlike the two-pass channel, the heat transfer is not improved but the pressure drop is still reduced for the four-pass channel. The second objective is to investigate the rotating effect on heat transfer and pressure drop in the cases of two-pass and four-pass channels for both original and modified designs. It is found out that heat transfer is improved with reduced pressure drop for all cases. However, the modified design results in the less improvement on heat transfer and lower reduced pressure drop as the rotation number increases. It can be concluded from the present work that the modification can solve the problem of pressure drop without causing the degradation of heat transfer for all cases. The two-pass channel with modified bend results in the highest heat transfer and the lowest pressure drop for rotating cases.

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