Abstract
To ensure a passable life span of gas turbine hot gas path components the measurement of metal surface temperature is paramount. Experimental analyses on internally cooled devices are often performed on simplified or scaled up geometries, which reduces the applicability of the results to the actual real hardware. A more reliable estimation of cooling performance could be obtained if the real engine component is directly studied. To achieve this goal, an experimental campaign is performed to investigate the internal heat transfer distribution of an industrial blade, cooled by means of an internal U-shaped channel. During the experiment the blade is heated to a known temperature, then a coolant is introduced through the internal channel to induce a thermal transient, during which the external surface temperature is measured with the help of an infrared camera. Then a transient thermal finite element simulation is performed with the same boundary and inlet conditions of the experiment. Based on the output of the simulation, the internal heat transfer distribution is updated until convergence between simulation output external temperature and the experimental temperature is achieved. In order to start the iterative procedure, a first attempt estimation of the internal heat transfer distribution is obtained with a lumped thermal capacitance model approach. Different experiments were performed with different mass flow rates and the results are compared with available literature data. The obtained results allow to observe detailed heat transfer phenomena, strongly bound to the relevant features of the actual real cooling system.
Highlights
The will of increasing gas turbine performance levels lead to growing values of turbine inlet temperature, which nowadays can significantly exceed the material temperature limits
The final heat transfer distribution is shown in the figure 5, which is obtained by implementing the proposed methodology on the test article considering the largest investigated Re value (Re mD Aμ : where m is the mass flow rate, D is the channel hydraulic diameter considered as reference length, A is the effective area and μ is the viscosity evaluated at the average film temperature during the test)
During the thermal transient the external surface temperature of the blade is recorded with the help of an Infared thermogarphy (IR) camera
Summary
The will of increasing gas turbine performance levels lead to growing values of turbine inlet temperature, which nowadays can significantly exceed the material temperature limits. In order to improve the life span of the gas turbine components various internal and external cooling schemes are used. To make these cooling schemes more efficient different cooling configurations are employed i.e. ribs, pins, dimples and impingement jets among others. More detailed review on the cooling enhancement techniques is given in book by Webb [1] and the developments in the gas turbine cooling are enlisted in the book by Han [2, 3]. Quantitative analysis of any gas turbine component cooling scheme is performed by predicting its heat transfer coefficient.
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