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.

Computational Study of Gas Turbine Blade Cooling Channel

2010 ◽  
Author(s):  
R. S. Amano ◽  
Krishna Guntur ◽  
Jose Martinez Lucci
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbine ◽  
Turbulence Models ◽  
Flow Patterns ◽  
Higher Order ◽  
Secondary Flows ◽  
Complex Flow ◽  
Cooling Performance ◽  
Cooling Channels

It has been a common practice to use cooling passages in gas turbine blade in order to keep the blade temperatures within the operating range. Insufficiently cooled blades are subject to oxidation, to cause creep rupture, and even to cause melting of the material. To design better cooling passages, better understanding of the flow patterns within the complicated flow channels is essential. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. Power output and the efficiency of turbine are completely related to gas firing temperature from chamber. The increment of gas firing temperature is limited by the blade material properties. Advancements in the cooling technology resulted in high firing temperatures with acceptable material temperatures. To better design the cooling channels and to improve the heat transfer, many researchers are studying the flow patterns inside the cooling channels both experimentally and computationally. In this paper, the authors present the performance of three turbulence models using TEACH software code in comparison with the experimental values. To test the performance, a square duct with rectangular ribs oriented at 90° and 45° degree and placed at regular intervals. The channel also has bleed holes. The normalized Nusselt number obtained from simulation are validated with that of experiment. The Reynolds number is set at 10,000 for both the simulation and experiment. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. The three-dimensional turbulent flows and heat transfer are numerically studied by using several different turbulence models, such as non-linear low-Reynolds number k-omega and Reynolds Stress (RSM) models. In k-omega model the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The outcome of this study will help determine the best suitable turbulence model for future studies.

Numerical Investigation of Secondary Flow Vortex Core Structure in the Two-Pass Rectangular Channel With 45° Ribs

2015 ◽  
Author(s):  
Jiangnan Zhu ◽  
Tieyu Gao ◽  
Jun Li ◽  
Guojun Li ◽  
Jianying Gong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Gas Turbine ◽  
Vortex Core ◽  
Side Wall ◽  
Main Flow ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Flow Vortex

The secondary flow which is generated by the angled rib is one of the key factors of heat transfer enhancement in gas turbine blade cooling channels. However, the current studies are all based on the velocity vector and streamline, which limit the research on the detailed micro-structure of secondary flow. In order to make further targeted optimization on the flow and heat transfer in the cooling channels of gas turbine blade, it is necessary to firstly investigate the generation, interaction, dissipation and the influence on heat transfer of secondary flow with the help of new topological method. This paper reports the numerical study of the secondary flow and the effect of secondary flow on heat transfer enhancement in rectangular two-pass channel with 45° ribs. Based on the vortex core technology, the structure of secondary flow can be clearly shown and studied. The results showed that the main flow secondary flow is thrown to the outer side wall after the corner due to the centrifugal force. Then it is weakened in the second pass and a new main flow secondary flow is generated at the same time near the opposite side wall in the second pass. The Nusselt number distribution has also been compared with the secondary flow vortex core distribution. The results shows that the heat transfer strength is weakened in the second pass due to the interaction between the old main flow secondary flow and the new one. These two secondary flows are in opposite rotation direction, which reduces the disturbance and mass transfer strength in the channel.

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.

Numerical Investigation of Heat Transfer and Flow Characteristics in a Steam-Cooled Square Ribbed Duct

2010 ◽  
Author(s):  
Linqi Shui ◽  
Jianmin Gao ◽  
Liang Xu ◽  
Xinjun Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Gas Turbine ◽  
Turbulence Model ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Friction Factors ◽  
Entry Pressure ◽  
Steam Cooling ◽  
Steam Superheat

In order to increase entry gas temperature and improve the efficiency of gas turbine, steam is used as a coolant instead of air. Much research has been carried out on the closed circuit steam cooling of vanes substituted with film-cooling using compressor air in recent years. Furthermore, by studying the steam flow and heat transfer characteristics in rib ducts, this investigation focuses on establishing the basis of steam cooling technology application in complex flow field of internally-cooled turbine vane. In this paper, a report and assessment of RSM method based on SSG turbulence model is performed with commercial computational fluid dynamics software ANSYS CFX. The numerical results of heat transfer coefficient and friction factors in square channels with 90 degree rib turbulators for Reynolds numbers of 10 000, 30 000 and 60 000 are compared with the experimental data from Han’s. It is found that the obtained heat transfer coefficient distributions and friction factors match well with SSG turbulence model. In addition, the heat transfer distribution and pressure drop of steam-cooled ducts are predicted under the same work conditions by using dry real gas model. The Reynolds number could be correlated with the Nusselt number. The impact of steam physical properties on heat transfer performance are researched detailedly by respectively changing the steam superheat and entry pressure. The results indicate that the RSM method with a suitable turbulence model is valuable for the air-cooled and steam-cooled duct with the acceptable engineering accuracy (less than 20%). Comparing the cooling efficiency between steam and air under the same operation condition, the advantage of using cooling steam is evident than using cooling air. Furthermore, the efficiency of the whole gas turbine system will be greatly improved through using the closed loop steam cooling system. Changing the steam superheat and entry pressure, it has little effect on the steam flow and heat transfer characteristics. Increasing the steam overheat would raise the friction factor. Contrarily, enhancing the entry pressure would decrease the friction factor.

Heat Transfer Characteristics of Blade Internal Tip Surface by Arrays of Delta-Winglet Vortex Generator Pairs

2020 ◽  
Author(s):  
Zhiqi Zhao ◽  
Lei Luo ◽  
Dandan Qiu ◽  
Xun Zhou ◽  
Zhongqi Wang
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Heat Transfer Performance ◽  
Internal Surface ◽  
Main Flow ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Bend Channel ◽  
Delta Winglet

Abstract This paper numerically investigated the effect of the arrays of the delta-winglet vortex generators (DWVGs) pairs on the flow field and heat transfer characteristics of gas turbine blade tip internal surface. Six different arrangements including three inclinations (30°, 45°, 60°) and two aspect ratios of DWVGs are calculated at Reynolds numbers ranging from 6000 to 14,000. The internal cooling passage of gas turbines are simplified as two-pass U bend channel and the U bend channel without any tabulators are considered as Baseline. The detailed flow structure, the evolution of vortices and heat transfer performance over the tip internal surface are presented. The results show that the arrays of DWVGs placed on the tip internal surface have great influence on the tip flow and heat transfer. Small-scale vortices are induced by the DWVGs, which have negligible impact on the main flow. Due to the nature of 180-deg turn, the impingement-like flow contributes the highest heat transfer performance. But too many DWVGs placed on the attachment region will weaken the energy of main flow and therefore reduce the local heat transfer. Besides, the blocked DWVGs (BVG) will enhance the heat transfer at the center line, and the guided DWVGs (GVG) will extend the low-energy flow cluster and thus weakening the heat transfer intensity. The results of this study are useful for understanding the mechanism of heat transfer characteristics in a realistic gas turbine blade by using the arrays of DWVGs.

Research on the Effects of Dimples and Protrusions on Flow and Heat Transfer in Matrix Cooling Channels in Turbine Blades

2019 ◽  
Author(s):  
Yigang Luan ◽  
Lianfeng Yang ◽  
Yue Yin ◽  
Pietro Zunino
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Heat Transfer Performance ◽  
Turbine Blades ◽  
Inlet Temperature ◽  
Transfer Performance ◽  
Turbine Inlet Temperature ◽  
Turbine Engine ◽  
Cooling Channels ◽  
Flow And Heat Transfer

Abstract Nowadays, gas turbine engines play an indispensable role in modern industry, which have been widely used especially in the aviation, marine and energy fields. The turbine inlet temperature is one of the most important factors that influences the performance of the turbine engine. It’s acknowledged that the higher turbine inlet temperature contributes to the overall gas turbine engine efficiency. Therefore, the internal cooling technology of turbine blades is of vital importance. This paper mainly studies the effects of dimples and protrusions on flow and heat transfer in matrix cooling channels and optimize the performance of the matrix cooling structure by numerical simulation and experiment methods. Thirteen cases have been calculated under Re = 10,000∼80,000 by the commercial code ANSYS Fluent. Structures with different layouts of dimples and protrusions were considered, such as the number, distance and the depth ratio. The original model has been strengthened due to the dimple and protrusion structure, which improves heat transfer performance as well as the thermal performance factor (TPF) on condition that the pressure loss increases slightly. Meanwhile, the optimized structures have been made and tested by the transient liquid crystal technique (TLC). A comparison between the CFD results and the experimental data is made. Note that the heat transfer performance is much better when the ratio of the dimple depth and the dimple diameter is equal to 0.3, compared with the ratio of 0.1 and 0.2. In terms of the cases with two sides dimples, the heat transfer can be enhanced by increasing the number of the dimples. In addition, the heat transfer performance is the best when both of dimples and protrusions are applied. Nu/Nu0 and TPF increase by up to approximately 7% and 5% respectively.

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