Novel cooling strategies for improved protection of gas turbine blades

Abstract

<p>Modern gas turbines are operating at peak turbine inlet temperature well beyond the maximum endurable temperature of turbine blade material. As a result, hot gas-contacting blades or vanes have to be cooled intensively by using various cooling technologies, such as film cooling and internal cooling, in order to increase the fatigue lifetime of the engine.</p> <p>In the present study, a series of experimental investigations were conducted to explore innovative cooling strategies for improved exterior and interior cooling of gas turbine blades. For the exterior cooling, the effectiveness of novel film cooling designs with coolant injection from Barchan-Dune-Shaped ramp (BDSR) and Barchan-Dune-Shaped injection compound (BDSIC) were evaluated in great detail, in comparison to that of conventional circular holes. While a high-resolution Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the dynamic mixing process between the coolant streams and the mainstream flows over the test plates, Pressure Sensitive Paint (PSP) technique was used to map the corresponding adiabatic film cooling effectiveness on the surface of interest based on a mass-flux analog to traditional temperature-based cooling effectiveness measurements. The measured effectiveness maps were correlated with the characteristics of the flow structures revealed from the detailed PIV measurement in order to elucidate underlying physics to explore/optimize design paradigms for a better protection of the critical components of turbine blades.</p> <p>Beside exploration of novel cooling designs for film cooling, an experiment was performed to examine the compressibility effect on film cooling effectiveness by using PSP and PIV technique. The experimental studies were conducted in a transonic, open-circuit wind tunnel located at Iowa State University. The measured effectiveness revealed that the mainstream compressibility has limited effect on film effectiveness, and the effectiveness of transonic speed flow can be studied in a relative low-speed wind tunnel.</p> <p>Pertinent to interior cooling of turbine blades, finally, an experimental investigation was also conducted to quantify the characteristics of the turbulent boundary layer flows over a dimpled surface. Many interesting flow features over the dimpled surfaces, such as the separation of incoming boundary layer flow at the dimple front rim, the formation and shedding of unsteady Kelvin-Helmholtz vortices over the dimple cavity, the impingement of the high-speed incoming flow onto the back rim of the dimple, and the generation of strong upwash flow over the back rim of dimple, were revealed clearly and quantitatively. This was found to correlate well with the enhanced heat transfer performance of dimpled surface design reported in previous studies.</p>