A Novel Experimental Technique for Investigating Natural Convective Heat Transfer in a Gas Turbine Annulus

Abstract

When a gas turbine is shut down it cools asymmetrically due to natural convection. After some time, a thermal gradient develops across the rotor drum as the top section cools slower than the bottom. This induces a thermal stress that causes the shaft to deflect — a phenomenon known as rotor or thermal bow. In some cases, this can lead to compressor tip rubs. All engines are affected by rotor bow to some degree. However, the mechanisms of natural convective heat transfer and impact of design features on rotor bow is not well understood; thus, the issue is not identified until late in the design stage, hampering an engines development. A novel experimental technique and facility has been developed that allows for accurate, detailed measurements of natural convective heat transfer in a gas turbine annulus to be made. The apparatus has the capacity to test circumferential and axial variations in temperature distribution, in addition to an isothermal wall boundary. An IR camera looking directly at the rotor surface is used to provide high-resolution heat transfer measurements. The test piece for this study consisted of a cylinder section and a conical section. Results from the isothermal cylinder test cases agreed quite well with previously published data, which gives confidence to the method that has been employed. The addition of a conical section had a profound effect on the results; however, more work is required before a method can be developed which will accurately predict the heat transfer coefficients based on initial temperature distribution. A 2D concentric cylinder methodology has also been developed that gives results in strong agreement with previously published data. Going forward, this new facility and the CFD method will be further developed to help quantify the effect of various design features on the natural convective heat transfer performance of a large civil gas turbine.

The Effect of Wall Thermal Boundary Condition on Natural Convective Shutdown Cooling in a Gas Turbine

“…A thin layer of rohacell, which is a very low conductivity structural foam (0.03 W/m 2 K), is adhered to the inner cylinder outer surface. This is used for infrared experiments [6].…”

Experimental and numerical investigations of mixed convection in turbine cavities for more flexible operations

“…Therefore, majority of the observations heavily rely on computational methods. Although a large body of literature has sought to provide experimental data for pure natural (for example Beckmann (1931), Liu et al (1961), Grigull and Hauf (1966), Kuehn and Goldstein (1976), and Fahy et al (2018)) and forced convection (Brighton (1963), Farias et al (2009) and Hosseini et al (2009) among others), mixed type of convection in the turbine casing cavities has not been previously assessed to a broad extent. The experimental investigations concerning the mixed type type of flows have been mostly on fully developed duct and pipe flows (for example Kotake and Hattori (1985), Ciampi et al (1987) and Mohammed et al (2010)).…”

Experimental and Numerical Investigations of Mixed Convection in Turbine Cavities for More Flexible Operations

“…Therefore, majority of the observations heavily rely on computational methods. Although a large body of literature has sought to provide experimental data for pure natural (for example Beckmann (1931) ; Liu et al (1961) ; Grigull and Hauf (1966); Kuehn and Goldstein (1976) ; Fahy et al (2018)) and forced convection ( Brighton (1963) ; Farias et al (2009) ; Hosseini et al (2009) among others), mixed type of convection in the turbine casing cavities has not been previously assessed to a broad extent. The experimental investigations concerning the mixed type type of flows have been mostly on fully developed duct and pipe flows (for example Kotake and Hattori (1985); Ciampi et al (1987) ; Mohammed et al (2010)).…”