Pedestal and Endwall Contribution in Heat Transfer in Thin Wedge Shaped Trailing Edge

Abstract

Short pin fins (pedestals) and long ribs (enlarged pedestals) are usually used in trailing edge cooling of turbine airfoils. To better reproduce the geometry of such cooling systems, test section of this experimental study is a wedge duct with inserts, to take into account effects of accelerating flow. A complete investigation of the system needs a separate evaluation of the heat transfer coefficients (HTC) for the pedestal surface and for the free endwall surface. In the present work an innovative technique made of different methods for these two different regions is presented, so cooling performances of each are evaluated. Thermochromic liquid crystal (TLC) transient technique is used to measure detailed heat transfer coefficients only on the endwall surface: a typical transparent (Plexiglas®) test article is used. Aluminum pedestals, employing a procedure based on a finite elements code, allow to measure the average heat transfer coefficient on the insert surface. To investigate the effects on transient technique of high conductive components, a comparison with Plexiglas inserts has been performed. Results show an underestimation of HTC with TLC transient technique only for aluminum long ribs at low Reynolds number values. Nevertheless the results seem to agree with other authors both for the endwall surface and for the entire cooling system.

Experimental Investigation of Innovative Internal Trailing Edge Cooling Configurations with Pentagonal Arrangement and Elliptic Pin Fin

“…The HTC of each pin fin is updated using the Newton convergence criterion, iterating until the temperature history evaluated with the FEM code matches the measured temperature history inside each pin. A moredetailed description of this procedure was reported by [15].…”

“…Typical uncertainties of the most important parameters are HTC = 12.2%, Re = 2.8%, f = 5.4%. More details about the individual contributions to the uncertainties of the single parameters for each of the measured physical properties are reported by [15]. the Mach number at 0.3.…”

“…With the same experimental method, [7,9,14] evaluated heat transfer and pressure losses in trailing edge cooling geometries typical of real blades: wedge and trapezoidal ducts, pin shape, and lateral flow effects were investigated. Lately, [15], besides the endwall HTC measurements with TLC, evaluated the pin fin contribution to heat transfer using high conductivity pedestals and an inverse data reduction method based on a finite element simulation of the transient test. Results shown that pin fins have higher HTC than the surrounding endwall surface.…”

Scrutiny of the Structural Stability of CMSX-4 and NIMONIC 901 made Gas Turbine Fixed blades with Showerhead Cooling

“…In some specific cases like aerospace applications as much high as 1,727°C [4][5][6], the pressure ratio also high at compressor about 50 [6]. In Such situations the components often encounter the thermal damages as well as other damages like melting, corrosion, oxidation and erosion [7], the degradation of local or global structural strengths of blades, vanes and other components and it was estimated that half of the lifespan of the blades gets reduced due to small temperature difference by improper cooling [3,6,9]. The specific damages are: blade trailing-edge cracks [8], buckling and risk of blade failure [11], thermal-fatigue [8,10,11].…”

“…In a thermal device like gas turbine the inlet temperature raised to improve the work output as well as efficiency. The rise of temperature usually 1000 to 1500°C [1][2][3]. In some specific cases like aerospace applications as much high as 1,727°C [4][5][6], the pressure ratio also high at compressor about 50 [6].…”