تحسين التبريد لممرات ريش التوربين باستخدام الاضلاع والطلاء الحاجز الحراري

Cooling Enhancement for Turbine Blades Passages by Using Ribs and Thermal Barrier Coating

   The flow and heat transfer in four elliptical cross sectional channels (having the same hydraulic diameter but different in channel aspect ratio) have been investigated at conditions that simulate those in air cooled turbine blades.
A numerical and experimental investigation of the effectiveness of using internal elliptical ribs of four different configurations (elliptical boot ship, triangular rib with right angle and with the flow direction, elliptical rib of two equal legs elliptical triangular rib with right angle, and inverse the flow direction) with the effect of the channel aspect ratio (AR=1,1.3,1.6 and 2) with and without thermal barrier coating has been conducted. The flow and heat transfer characteristics for a fully developed turbulent flow in an elliptical channel heated with constant surrounding temperature and Reynolds numbers based on channel hydraulic diameter values of (11000, 13500, and 16000) has been tested in this study.
The numerical simulation study includes solving the three dimensional governing equations (Continuity, Reynolds Averaging Navier-Stokes and Energy equations) in turbulent regime with (k-ε) model as the perfect model using the FLUENT software version (16.1). The effect of different ribs geometries with rib height to hydraulic diameter ratio (e/Dh=0.135) and rib-rib spacing (pitch) to rib height ratio (p/e=10) in an elliptical channel of 0.5 m long, internal cross section of (57×29 ,50×31, 43×33, 37×37) mm and 1.5 mm wall thickness were simulated. Four different configurations of ribs named as rib (1, 2, 3, and 4).

   In the experimental part of this study, a rig was designed and constructed to simulate conditions in gas turbine blade. The operational conditions are: inlet coolant air temperature of 300 K and the surrounding constant hot air temperature of (673K). The considered cases were compared with a smooth elliptical channel (channel without ribs) at the same operational conditions. The channel with AR (2) was the best channel in heat transfer, and the channel with ribs provided higher thermal performance than the smooth ones. The ribbed channels (rib1, rib 2, rib3, and rib 4) increased the Nusselt number and thermal performance factor by (5.0, 4.8, 2.4 and 1.4) and (2.31,1.87,1.09 and 0.55) times, respectively when it is compared with the smooth channel case.
Case of rib 1 fitted in channel with AR (2) showed the best result (lower pressure drop and higher heat transfer enhancement). While case of rib 4 fitted in channel of AR (2) showed the worst result. The experimental and numerical results were compared and showed a good agreement with a maximum difference of (3.8%).
The additional work involves coating the channel of the best case with composite Nano-materials (thermal painting mixed with Yttrium oxide nanoparticle (Y2O3) by (5wt. %) as a thermal barrier coating. Nusselt number was enhanced for the channel with coating by (9.97%) times the case of channel without coating.