No abstract

Gas turbine blades are usually cooled by using ribbed serpentine internal cooling passages, which are fed by extracted compressor air. The individual straight ducts are connected by sharp 180 deg bends. The integration of turning vanes in the bend region lets one expect a significant reduction in pressure loss while keeping the heat transfer levels high. Therefore, the objective of the present study was to investigate the influence of different turning vane configurations on pressure loss and local heat transfer distribution. The investigations were conducted in a rectangular two-pass channel connected by a 180 deg sharp turn with a channel height-to-width ratio of H/W=2. The channel was equipped with 45 deg skewed ribs in a parallel arrangement with e/dh=0.1 and P/e=10. The tip-to-web distance was kept constant at Wel/W=1. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Furthermore static pressure measurements were conducted in order to determine the influence of turning vane configurations on pressure loss. Additionally, the configurations were investigated numerically by solving the Reynolds-averaged Navier–Stokes equations using the finite-volume solver FLUENT. The numerical grids were generated by the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f turbulence model. The results showed a significant influence of the turning vane configuration on pressure loss and heat transfer in the bend region and the outlet pass. While using an appropriate turning vane configuration, pressure loss was reduced by about 25%, keeping the heat transfer at nearly the same level in the bend region. An inappropriate configuration led to an increase in pressure loss while the heat transfer was reduced in the bend region and outlet pass.

Numerical investigations of a two-pass internal cooling channel with engine representative cross-sections related to turbine blade cooling were conducted. The channel consisted of a trapezoidal leading edge pass, a sharp 180° bend, and a nearly rectangular outlet pass. The numerical predictions were validated against experimental results in terms of pressure distributions, total pressure losses, and local heat transfer coefficient distributions. The investigations focused on the influence of rib turbulators and tip-to-web distance on the pressure loss and heat transfer. The channel was equipped with skewed ribs (α = 45°, P/ e = 10, and e/ dh = 0.1) in a parallel and a staggered configuration. The dimensionless tip-to-web distance Wel/ dS was varied from 0.6 to 2.0. The investigated Reynolds number was 50 000. The computational study was performed by solving the Reynolds-averaged Navier—Stokes equations with the commercial finite-volume-solver FLUENT and three turbulence models: the realizable k—ε turbulence model with a two-layer wall treatment, the k—ω—SST model, and the v2– f model. The computations were performed on hybrid, unstructured grids created with the semi-automatic grid generator CENTAUR. The predictions using the k—ω—SST model were in overall agreement with the experimental results, showing an increasing pressure loss with a decreasing tip-to-web distance while the heat transfer was increased to a smaller extent.

In the present study, a two-pass internal cooling channel with engine-similar cross-sections was investigated numerically. The channel featured a trapezoidal inlet pass, a sharp 180 deg bend, and a nearly rectangular outlet pass. Calculations were done for a configuration with smooth walls and walls equipped with 45 deg skewed ribs (P/e=10, e/dh=0.1) at a Reynolds number of Re=50,000. The present study focused on the effect of rotation on fluid flow and heat transfer. The investigated rotation numbers were Ro=0.0 and 0.10. The computations were performed by solving the Reynolds-averaged Navier–Stokes equations (Reynolds-averaged Navier–Stokes method) with the commercial finite-volume solver FLUENT using a low-Re shear stress transport (SST) k-ω turbulence model. The numerical grids were block-structured hexahedral meshes generated with POINTWISE. Flow field measurements were independently performed at German Aerospace Centre Cologne using particle image velocimetry. In the smooth channel, rotation had a large impact on secondary flows. Especially, rotation induced vortices completely changed the flow field. Rotation also changed flow impingement on the tip and the outlet pass sidewall. Heat transfer in the outlet pass was strongly altered by rotation. In contrast to the smooth channel, rotation showed less influence on heat transfer in the ribbed channel. This is due to a strong secondary flow field induced by the ribs. However, in the outlet pass, Coriolis forces markedly affected the rib induced secondary flow field. The influence of rotation on heat transfer was visible in particular in the bend region and in the second pass directly downstream of the bend.

Gas turbine blades are usually cooled by using ribbed serpentine internal cooling passages which are fed by extracted compressor air. The individual straight ducts are connected by sharp 180° bends. The integration of turning vanes in the bend region lets one expect a significant reduction in pressure loss while keeping heat transfer levels high. Therefore, the objective of the present study was to investigate the influence of different turning vane configurations on pressure loss and local heat transfer distribution. The investigations were conducted in a rectangular two-pass channel connected by a 180° sharp turn with a channel height-to-width ratio of H/W = 2. The channel was equipped with 45° skewed ribs in a parallel arrangement with e/dh = 0.1 and P/e = 10. The tip-to-web distance was kept constant at Wel/W = 1. Spatially resolved heat transfer distributions were obtained using the transient thermochromic liquid crystal technique. Furthermore static pressure measurements were conducted in order to determine the influence of turning vane configurations on pressure loss. Additionally, the configurations were investigated numerically by solving the Reynolds-Averaged Navier-Stokes equations (RANS method) using the Finite-Volume solver FLUENT. The numerical grids were generated by the hybrid grid generator CENTAUR. Three different turbulence models were considered: the realizable k-ε model with two-layer wall treatment, the k-ω-SST model, and the v2-f turbulence model. The results showed a significant influence of the turning vane configuration on pressure loss and heat transfer in the bend region and the outlet pass. While using an appropriate turning vane configuration pressure loss was reduced by about 25% keeping the heat transfer at nearly the same level in the bend region. An inappropriate configuration led to an increase in pressure loss while heat transfer was reduced in the bend region and outlet pass.