Session: 15-02 Swirling Flow / Swirl Chambers

Paper Number: 82775

82775 - Heat Transfer Enhancement of Swirl Cooling by Different Crossflow Diverters 

Swirl cooling is a promising cooling technology in gas turbine blade leading edge. It can promote the radial convection of coolants, produce a large near-wall pressure gradient, thin the thermal boundary layer, and improve turbulent kinetic energy, thus greatly enhancing the target wall heat transfer. However, the swirl strength of coolant decreases rapidly along the swirl chamber, so there exists a low heat transfer zone between two adjacent nozzles, and there is an ultra-low heat transfer coefficient band in the low heat transfer zone, which would lead to large temperature gradients and thermal stresses. Moreover, the circumferential component of coolant decreases while the axial component increases along the swirl chamber, thus forming a crossflow and deflecting the downstream jets.

To solve this problem, this paper proposed the concept of swirl cooling with crossflow diverters, and investigated the flow and heat transfer characteristics. Numerical simulations were performed by using 3D steady flow solver of Reynolds-averaged Navier-Stokes equations (RANS). The turbulence model validations were performed against both smooth swirl chamber and tube with circumferential ribs, and the validation results pointed out that the SST k-ω turbulence model had the highest accuracy in predicting the heat transfer in swirl chamber with diverters. To reveal the mechanism of crossflow suppression and heat transfer enhancement, the simulation results were compared with smooth swirl chamber under different Reynolds numbers. On this basis, the effects of crossflow diverter locations and shapes were studied further.

The results showed that for smooth swirl chamber, the swirl strength decayed linearly, and the heat transfer coefficients decreased rapidly, thus the high heat transfer zone cannot cover the whole region between two adjacent nozzles. The circumferential velocity of the jet gradually decreased while the axial velocity increased, thus forming the cross flow. Cross flow and downstream nozzle efflux produced interference effect. Because of friction effect, cross flow reduced the circumferential velocity of the downstream jets and made the jet deflect downstream. Thus, the high heat transfer area of the downstream target plane decreased sharply. For swirl chamber with crossflow diverters, the cross-flow and downstream jets separated from each other. The ability of the downstream jet to penetrate the main stream and scour the target surface was strengthened. Therefore, the heat transfer of the target surface near the downstream nozzle was enhanced. Moreover, the crossflow diverters also acted as turbulator, and the low heat transfer zone between two adjacent nozzles was eliminated. When the crossflow diverter was located closed to downstream nozzle in every pitch, the heat transfer enhancement effect was most obvious. Besides, the crossflow diverter with a square cross section generated the best comprehensive thermal performance.

Presenting Author: Kun Xiao Xi'an Jiaotong University

Presenting Author Biography: Kun Xiao is a Phd candidate from Xi'an Jiaotong University, and he is major in turbine blade internal cooling.

Authors:

Kun Xiao Xi'an Jiaotong University
Juan He Xi'an Jiaotong University
Zhenping Feng Xi'An Jiaotong University