Gas turbine blade cooling technology

Gas turbine performance can be enhanced by increasing the temperature of the flow entering the turbine section. Increasing the turbine inlet temperature, however, causes problems for the turbine blades. The operating temperature of the gas turbine is typically higher than the melting point of turbine blade materials. When the local variation of the blade temperature is intensified, thermal stress is generated on the blade. Moreover, when this thermal stress is maintained for a long time, the blade may experience creep and possibly failure.

To overcome these issues, turbine blades utilize both internal convective cooling and external film cooling, as shown in Figure 1.

Figure 1. Schematic of a modern gas turbine blade with various cooling techniques [1].

Gas turbine blades have complex internal cooling passages which consist of structures to efficiently dissipate the heat. The goal of internal cooling is to achieve optimal thermal protection, while using as little coolant as possible and minimizing the pressure drop of the coolant in the flow path. Experimental and numerical techniques are utilized for estimating thermal performance. Magnetic resonance velocimetry (MRV) can quantitatively visualize complex internal cooling flows using a medical MRI scanner, and infrared thermography measures the resulting heat transfer. In addition, computational fluid dynamics (CFD) methods such as Reynolds-averaged Navier-Stokes (RANS) analysis and large eddy simulation (LES) are utilized for numerical analysis of cooling flow and heat transfer.

We are currently focusing on internal cooling in the trailing edge. In general, convective cooling inside the internal passage of a trailing edge is often insufficient when trailing edge cooling slots are not present. Thus, it is necessary to make more of the flow pass through the sharp corner in the internal channel. We are investigating the effect of rib turbulators by quantitatively visualizing the flow structure and heat transfer using MRV and IR thermography (Figure 2). Furthermore, by conducting high fidelity LES, we can elucidate the detailed flow structure around the ribs, which is difficult to obtain by MRV due to limited spatial resolution (Figure 3). Additionally, using a RANS simulation, we visualized the vortex structure which enhances the wall heat transfer (Figure 4).

Figure 2. Experimental measurement of cooling flow in the trailing edge. (a) Streamwise velocity distribution using MRV [2] and (b) surface heat transfer measurement using IR thermography [3].

Figure 3. (a) Streamwise velocity distribution of cooling flow in the trailing edge, and (b) streamwise velocity contour with streamlines, on a plane near the ribbed wall, computed using LES [2].

Figure 4. Vortex characteristics of internal cooling passage in the trailing edge [3].

[1] Han, J.C., & Rallabandi, A.P. (2010). Turbine Blade Film Cooling Using PSP Technique. Frontiers in Heat and Mass Transfer, 1, 013001.
[2] Baek, S., Lee, S., Hwang, W., & Park, J. S. (2019). Experimental and numerical investigation of the flow in a trailing edge ribbed internal cooling passage. Journal of Turbomachinery, 141(1), 011012.
[3] Kim, S., Suh, S., Baek, S., & Hwang, W. (2020). Influence of ribs on internal heat transfer and pressure drop in a turbine blade trailing edge channel. Proceedings. ASME Turbo Expo 2020, GT2020-14847.