Internal blade cooling: The Cinderella of computational and experimental fluid dynamics research in gas turbines

Abstract

The paper reviews experimental and computational research directed at improving the internal cooling of gas-turbine blades. While not the most glamorous area of gas-turbine aerothermodynamics, the improvements in overall thermal efficiency directly attributable to internal blade cooling arguably outstrip those achieved in any other area of jet-engine research. The cooling arrangements within a blade adopt three cooling strategies: impinging leading-edge jets, serpentine passages for the mid-blade section, and pin fins near the trailing edge. Progress in each of these areas is examined. Although, in the second of these areas, CFD studies have now become an essential weapon in the designer's armoury, the other two still rely mostly on experimental research. Possible further developments are discussed.

Heat transfer of a radially rotating furrowed channel with two opposite skewed sinusoidal wavy walls

“…Despite of the potentials for blade cooling applications, no heat transfer result is available for a rotating wavy channel to date. To obtain the full Nu scan over rotating channels, the naphthalene sublimation method and the transient/steady-state liquid crystal thermometry [8,9,13,31,32] have been previously applied. But none of these studies can successfully reveal the rotating buoyancy effects.…”

“…The back surface of the wavy heating foil (6) is painted black to increase its emission. Each end of the heating foils (5)(6) is squeezed between the two-piece entry (8) or exit (9) copper plates which are respectively sandwiched between the flow entry/exit flanges (2)(3) and the back/front Teflon walls (4)(7). Two Teflon channel side-walls (11)(12) with the waviness to fit the front and back wavy foils (5)(6) set the channel height (H) of 13.5 mm, which gives the channel aspect ratio (W/H) of 4.…”

“…By way of varying the sectional shape of the non-circular rotating channel in respect to its axis of rotation, the flow structures and their HTE performances are modified. Local HTE performances in the rotating channels are dependent on the shape [1], the aspect ratio [13] and the orientation [5,9] of a rotating channel. For rotating pin-fin channels fitted with pin-fins, which serve as another mainstream of HTE devices as a part of internal cooling network at the trailing edge of a rotor blade, the Coriolis secondary flows are constantly disturbed by these pin-fins.…”

Improved Eddy-Viscosity Modelling of Turbulent Flow around Porous–Fluid Interface Regions

“…Roughened surfaces, such as those formed by placing ribs on the surface, across the flow direction, effectively enhance the heat transfer due to flow separation and reattachment behind each rib that disrupts the thermal boundary layer. In the case of a surface roughened by a solid rib, however, a hot spot occurs at the circulation zone, leading to deterioration of heat transfer around the rib region (Iacovides and Raisee 1999;Iacovides and Launder 2007). To overcome this issue, several investigations have been performed using different techniques to change the geometry of the rib, and the use of perforated ribs is one of these techniques.…”

Secondary flow and heat transfer coefficient distributions in the developing flow region of ribbed turbine blade cooling passages

“…However, only a few have explicitly linked the aerodynamics within the passage to the spatial distributions of heat transfer coefficient (Rau et al 1998;Casarsa and Arts 2005;Arts 2006). Some (Casarsa and Arts 2005;Iacovides and Launder 2007) discuss the importance of combined aerodynamic and heat transfer data. For true numerical code validation, combined studies are required to fully understand why discrepancies are occurring, and where detailed flow features are not captured.…”