Analysis of vortex cooling fluid-structure interaction under different vortex chamber curvature

https://doi.org/10.1016/j.ijthermalsci.2021.107154Get rights and content

Highlights

  • Interaction between blade solid and vortex cooling is studied by fluid-structure coupling method.

  • Vortex cooling flow and heat transfer characteristics, solid region stress and displacement characteristics are researched.

  • Vortex chamber curvature is changed.

Abstract

The vortex cooling with cascade channel and blade leading edge solid region is established. The flow and heat transfer properties of vortex cooling region, and the stress and displacement properties of blade solid region are analyzed by the fluid-structure interaction method. The ellipses edges with vertical axis to horizontal axis ratio a/b of 0.48, 0.72, 1.00, 1.31 and 1.73 are utilized to form the vortex chamber with different curvature. Influences of vortex chamber curvature on the vortex cooling fluid-structure interaction characteristics are researched to reveal the vortex cooling high heat transfer mechanism deeply. Results show that, for a/b decreasing from 1.73 to 0.48, the overall average Nusselt number and comprehensive heat transfer factor will first increase and then decrease, and the drag coefficient will gradually decrease. As a/b decreases, the high Nusselt number region moves from the target wall next to the nozzle to the target wall under the nozzle and at the vortex chamber bottom. With decreasing a/b, the thermal stress and thermal displacement on the blade pressure surface gradually decrease, while on the blade suction surface the thermal stress first decreases and then increases, and the thermal displacement first increases, then decreases and finally increases. In this study, compared with a/b = 1.73, the heat transfer performance for a/b = 0.72 has been enhanced by 21.00% and can provide the best protection for the blade.

Introduction

The gas turbine performance improves gradually with the increasing gas temperature. At present, the inlet gas temperature of H-class gas turbine can reach above 1600 °C. Obviously, this temperature has been far beyond the blade material thermal limit. As a result, the first few stage turbine blades will be exposed to the high temperature gas and bear serious heat load. Especially for the blade leading edge surface region, the blade is directly scoured by high speed hot gas and working conditions are particularly severe. Therefore, it is vitally important to protect the blade leading edge from thermal erosion. For the blade leading edge, impingement cooling is the most popular internal cooling method due to its high local heat transfer performance.

Many researches have been conducted on different impingement chamber structures for impingement cooling. Yang et al. [1] realized the impingement nozzles series-linked arrangement by changing the impingement chamber structure. They found that arranging nozzles in series could increase the heat transfer at the upstream and downstream target walls, but would produce a higher pressure drop. Ramakumar et al. [2] numerically explored the flow and heat transfer characteristics of nozzle jets impacting target walls with different curvature, and the influence of coolant Reynolds number, nozzle-to-surface distance, and nozzle spacing were considered. Numerical results indicated that the impingement chamber with large curvature had a higher heat transfer rate, and for semicircular impingement chamber, the experimental heat transfer results were in good agreement with the simulated data. Zhang et al. [3] experimentally and numerically studied for the influence of the impingement chamber curvature, coolant-to-mainstream density ratio and blowing ratio. They proposed that the heat transfer performance was better when the impingement chamber curvature was low at a low density ratio, and the low impingement chamber curvature had the same heat transfer performance as the high impingement chamber curvature at a high density ratio. Wang et al. [4] numerically investigated the effect of nozzles arrangement, jet Reynolds number and the blade leading edge curvature. It was shown that the nozzles in-line arrangement, the increasing of nozzle-to-surface spacing to jet diameter ratio and Reynolds number were beneficial to the heat transfer enhancement. Singh et al. [5] carried out experimental and numerical studies on the flow and heat transfer phenomenon with different shower head arrangements, and the coolant Reynolds number and chamber curvature were changed. They observed that the increasing impingement chamber curvature could promote the growth of the Taylor Gottler vortex and enhance the heat transfer.

However, impingement cooling is severely affected by the cross flow, and the heat transfer capability of the downstream target wall is poor. So an internal cooling method double vortex cooling that can effectively reduce the cross flow is formed, and many studies have explored the influence of different double vortex chamber structures. Fan et al. [6] numerically compared the performance of different cooling methods, and configurations of impingement cooling, vortex cooling and double vortex cooling were established. Results presented that the double vortex cooling streamline was similar to that of impingement cooling, and since double vortex cooling would accelerate the coolant, the double vortex cooling coolant velocity at the target wall was higher. Mousavi et al. [7] compared vortex cooling with double vortex cooling, and numerically investigated the characteristics of different nozzle numbers in cylindrical vortex chamber cross section. It is found that the increased nozzles number in the cross section could generate strong vortices and increase the Nusselt number. Zhou et al. [8] numerically investigated the influence of different double vortex chambers on the flow and heat transfer characteristics, and five double vortex chambers were formed by two overlapping elliptical cylinders with different aspect ratios. They pointed out that the double vortex chamber wall with larger curvature produced the lowest flow loss, the largest overall average Nusselt number and the best thermal performance. As the double vortex chamber curvature decreased, the heat transfer distribution on the target wall became more uniform. Kusterer et al. [9] presented a numerical study of establishing five types double vortex cooling with different chamber structures. Their results suggested that the best heat transfer performance appeared when the double vortex chamber bottom curvature was smaller and the top curvature was higher.

But the arrangement of double vortex cooling is limited by the blade. Therefore, as a new internal cooling method, vortex cooling has attracted more and more attention due to its strong heat transfer ability and uniform advantages. Alhajeri et al. [10] numerically explored the flow and heat transfer performance with adding ribs to the vortex chamber target wall. It was noteworthy that the vortex chamber wall roughness had a great influence on the coolant velocity, heat transfer and pressure drop. Liu et al. [11] conducted simulation for a vortex chamber wall with dimples in different diameters. Results revealed that the total heat transfer of the vortex chamber wall with dimples was increased, and the pressure loss was reduced. Wang et al. [12] researched the flow and heat transfer performance in the vortex chamber with variable cross section and the effect of different chamber draft angles. They proposed that with the increase of chamber draft angle, the heat transfer capacity increased and the pressure loss decreased. Jiang et al. [13] numerically researched the water mist cooling heat transfer performance in NASA C3X vane target wall and the effect of mist concentration, mist diameters, inlet temperature and jet velocity were presented and analyzed. Results showed that water mist cooling had greatly improved the heat transfer performance. Fan et al. [14] arranged film holes on the vortex chamber target wall and numerically explored the influence of the film holes on the vortex cooling flow and heat transfer characteristics. It was proposed that the film holes had a strong disturbance to the coolant flow in the vortex chamber, which increased the film hole upstream velocity and reduced the downstream velocity.

Although many studies on vortex cooling flow and heat transfer properties have been conducted, few concerns have observed about the association between the vortex cooling and blade solid. The majority of studies on vortex cooling is to apply a constant temperature or heat flux boundary condition at the target wall. During the gas turbine period of operation, the high temperature gas drives the blades to perform work and transfers heat to blades, and the heat is further transferred to the coolant by blade heat conduction, so that the boundary conditions of the target wall are determined. Meanwhile, the blade solid region will be affected by the aerodynamic and thermal loads. Therefore, the fluid-structure interaction analysis for the blade is of major importance for the blade protection. Recently, the fluid-structure interaction model is often used to explore the characteristics of blades in complex flow fields. Prapamonthon et al. [15] numerically explored and analyzed the thermal characteristics of turbine blades with thermal barrier coatings at two inlet temperatures and turbulence intensities by the fluid-structure interaction model. They discovered that the change in inlet temperature had a greater impact than that in turbulence intensity. Zheng et al. [16] numerically studied the three-dimensional flow characteristics of the axial flow turbine entire flow passage by the fluid-structure interaction model. Results indicated that compared with the pure flow simulation, the fluid-structure interaction model not only changed the flow field distribution, but also had a greater impact on the blade stress. Zhu et al. [17] conducted a numerical simulation to study the difference between the unsteady flow field and structural vibration of the wind turbine blade under unidirectional and bidirectional fluid-solid coupling. They concluded that the stress on the leeward side of the blade under two-way coupling was slightly higher than that under one-way coupling. Sajedin et al. [18] established a fluid-structure interaction model of a full-scale turbocharger turbine blade, and the blade aerodynamic load and structural response was determined to use the FEA model. Results presented that the most effective way to improve the blade performance was to reduce the blade leading edge thickness. Pujari et al. [19] numerically investigated the influence of conjugate heat transfer on the first-stage nozzle vane of the high-pressure gas turbine with film cooling holes. It showed that the local temperature distribution in the blade solid region largely depended on the coolant flow distribution inside and outside the blade. El-Jummah et al. [20] established an impingement cooling model with solid region, and compared the simulation with experiment data. They noted that the fluid-structure interaction was sufficient to predict the metal temperature in the gas turbine cooling system, and was applied to the optimization study of the best cooling configuration.

Several details are worth noting in the large number of studies mentioned above. In previous studies of impingement cooling and double vortex cooling, the vortex chamber curvature was changed and the influence of vortex chamber curvature on the cooling performance was explored. Most of the previous studies have simplified gas turbine blade leading edge into cylindrical and semi-cylindrical shapes, and did not consider the vortex chamber curvature change for vortex cooling. Indeed, the vortex chamber curvature showed an important influence on the vortex cooling flow properties and heat transfer performance. It is significant to choose an appropriate vortex chamber curvature for gas turbine design. Other than that, there are few researches on the fluid-structure interaction of vortex cooling. In order to fully consider the blades working environment, it is necessary to perform fluid-structure interaction analysis on vortex cooling.

In the present work, vortex cooling model with cascade channel and leading edge solid region is constructed. The flow and heat transfer properties of vortex cooling region, the stress and displacement properties of solid region under aerodynamic and thermal loads are explored. The interaction between the fluid and solid region is studied by fluid-structure interaction model. In addition, in order to meet the cooling characteristics for the actual blades, based on the original C3X vane vortex chamber, ellipses with different vertical and horizontal axis ratios are used to replace the vortex chamber leading edge, thereby forming the vortex chamber with different curvature. The influence of the vortex chamber curvature on the vortex cooling fluid-structure interaction is studied. This paper studies the vortex cooling fluid-structure interaction mechanism and explores the vortex chamber curvature with better flow properties and heat transfer performance.

Section snippets

Geometrical details

Fig. 1 presents the vortex cooling fluid-structure interaction model, consisting of the vortex cooling, blade leading edge solid and cascade channel region. The detailed experimental measurements of pressure and temperature distribution for C3X vane have been performed by NASA [21], and the experimental data obtained have been widely used as standard data in the research of the coolant flow and heat transfer. Based on these reasons, the blade is chosen as C3X vane. Fig. 2(a) shows the vortex

Vortex cooling flow characteristics

The flow properties are inextricably linked to the heat transfer Heat transfer capacity. In this section, the flow characteristics of the vortex cooling region are analyzed. Fig. 6 shows the three-dimensional streamlines distribution and colored by velocity for vortex chamber curvature a/b = 0.72. For vortex cooling region, the coolant from the coolant chamber inlet enters the vortex chamber to generate a high-speed rotating flow, and the streamlines with a lower speed appear at the rotation

Conclusions

In this study, a vortex cooling fluid-structure interaction model with cascade channel and blade leading edge solid region is created. The high temperature gas, vortex cooling coolant and blade solid interaction is explored. In addition, the vortex chamber with different curvature is formed by ellipses with the vertical axis to horizontal axis ratio a/b of 0.48, 0.72, 1.00, 1.31, and 1.73. Influences of vortex chamber curvature on vortex cooling performance are researched. The main conclusions

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors gratefully acknowledge financial support from Science and Technology Research Project of Jilin Provincial Department of Education (JJKH20210091KJ).

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