From an economic perspective coupled with the even more awareness about the environmental aspect, there is a strong push to develop higher efficiency gas turbine engines. The designers aim to increase the turbine inlet temperature in favour of the best cycle performance, which in turns requires more and more efficient cooling systems for the hot gas path components. Nowadays, the numerical simulation tools facilitate the cooling system development and design, but the geometrical complexity and working conditions make very complicated their thermodynamic study. Therefore, experimental investigation remains essential to obtain detailed information on aerothermal performances.

The internal forced convection is one of the most used techniques to thermally protect the turbine blade and, over the past decades, numerous works were focused on the heat transfer distribution into different cooling channel geometries.

In realistic conditions, the inner surfaces of the channel are subject to different heat fluxes and temperatures, which establish local air density difference. This induces buoyancy effects that in turn would change the flow field during rotation, and consequently the local heat transfer coefficients. Whereas, only the investigated surfaces are commonly heated when optical accessibility is required in the experimental setup. Nevertheless, few contributions in literature have addressed the influence of the wall heating conditions on the heat transfer distribution.

In the past, the heat transfer was investigated in a rotating two-pass square channel with different turbulators configurations and walls heating conditions \[1,2,4\]. Despite the low spatial resolution of the available data (as area-averaged), it can be concluded that uneven wall temperature has a significant impact on the heat transfer as the rotation number is increased.

More recently, Wang et al. \[3\] obtained similar results but with a numerical approach.

This work experimentally investigates the impacts of wall heating condition on heat transfer distribution for a simple rotating channel. The model has a square cross-section with a hydraulic diameter of 50 mm and a ribbed wall. The ribs are at 90 deg to the main flow direction, the rib pitch-to-height ratio is 10, and the blockage is 10%. High spatial resolution heat transfer distributions measurements were carried out by means of liquid crystals thermography in two thermal boundary conditions: only ribbed wall heated or ribbed wall and sidewalls with same heat flux. Inlet Reynolds number was fixed at 20000 and the tests were carried out in both in static and rotating condition up to Rotation number of 0.18, in which the ribbed wall acted as trailing edge side.

The results show that the different wall heating conditions have a negligible impact on the stationary case but have a great influence when the rotation takes place with modification of the heat transfer distribution with an overall enhancement.

 

\[1\] J.C. Han, Y.M. Zhang (1992). *Effect of Uneven Wall Temperature on Local Heat Transfer in a Rotating Square Channel With Smooth Walls and Radial Outward Flow.* Journal of Turbomachinery, 114(4): 850-858

\[2\] J.A. Parsons, J.C. Han, Y.M. Zhang (1994). *Wall heating effect on local heat transfer in a rotating two-pass square channel with 90° rib turbulators*. International Journal of Heat and Mass Transfer, 37(9): 1411-1420

\[3\] Z. Wang, R. Corral (2017). *Numerical study of effect of wall heating condition on heat transfer performance of rotating internal cooling channel.* Conference Proceeding of 12^th^ ETC-357

\[4\] Y.M. Zhang, J. C. Han, J.A. Parsons, C.P. Lee (1995). *Surface Heating Effect on Local Heat Transfer in a Rotating Two-Pass Square Channel With 60 deg Angled Rib Turbulators*. Journal of Turbomachinery, 117(2): 272-280


Heat Transfer Characterization Inside a Rotating Rib Roughened Cooling Channel With Multiple Heated Walls

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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