Gas turbine blade internal cooling: design, development, and validation of a new rig for heat transfer measurements under rotation.

Abstract

The contribution describes part of the work carried out on a wider research project aimed to set up a new tool to study rotational effects on the heat transfer distribution inside realistic cooling passages for gas turbine blades. Transient thermochromic liquid crystals (TLC) measurement technique is chosen in order to obtain spatially resolved heat transfer data. This obliges to perform the transient measurements with a cold temperature step on the coolant flow, in order to replicate correctly the buoyancy effects induced by rotation. This target is achieved by a new facility which components and working principle have been the subject of previous contributions. In the present paper, the progresses made in the development of the data processing methodology are described at first. Successively, a first step into the demanding rig and methodology validation process is commented by exploiting the results of a wide test campaign on a simple cooling channel geometry. KEYWORDS Internal cooling, rotation, liquid crystals, transient, gas turbine NOMENCLATURE Bo buoyancy parameter Ro rotation number cmat Plexiglas specific heat capacity e rib height Dh hydraulic diameter T0 initial temperature h heat transfer coefficient Tb bulk flow temperature H channel height Tw wall temperature K thermal conductivity Ub bulk flow velocity L channel length W channel width Nu Nusselt number ρ air density Nu0 reference Nusselt µ air dynamic viscosity P rib pitch Θ non-dimensional temperature R evaluation radius Ω rotational speed Re Reynolds number mat refers to material properties Ro rotation number air refers to air properties

Validation of the Transient Liquid Crystal Thermography Technique for Heat Transfer Measurements on a Rotating Cooling Passage

“…An in-house developed processing software written in Matlab (R2013b, MathWorks, Natick, MA, USA) has been used to perform the heat-transfer computation, namely camera calibration, computation of flow-temperature distribution, image processing in order to get the LC activation time, and solution of Equation (6). The software has been developed over the years, and the details about the implemented algorithm can be found in [14,27].…”

“…Therefore, a sudden temperature drop on the flow instead of a flow heating should be imposed to satisfy the similarity with real working conditions. Pagnacco et al [14] applied the transient LCT technique to study the heat-transfer distribution in a rotating square ribbed channel at a Reynold number equal to 10,000 and rotation number up to 0.4. The authors highlighted the different heat-transfer behaviour and opposite buoyancy effects depending on the direction of the flow-temperature change realized on the airflow (i.e., cold or hot variations).…”