Film cooling extraction effects on the aero-thermal characteristics of rib roughened cooling channel flow

The present study is geared towards quantifying the effects of film cooling holes on turbine internal cooling passages. In this regard, tests are conducted in a generic stationary model, with evenly distributed rib type perturbators at 90°, constituting a passage blockage ratio of H/Dh=0.3 and pitch-to-height ratio of P/H=10. The 1/3H diameter surface-perpendicular film cooling holes are employed at a distance of 5/3H downstream of the preceding rib. Through liquid crystal thermometry measurements, the aero-thermal effects of a change in suction ratio are contrasted for various configurations (Re=40,000 SR=0-6), and compared with the analogous aerodynamic literature, enabling heat transfer distributions to be associated with distinct flow structures. At increased suction ratio, the size of the separation bubble downstream of the rib is observed to diminish, triggering globally an earlier reattachment, in addition to low-momentum hot fluid extraction via film cooling suction. Hence, in the presence of active flow extraction, higher overall heat transfer characteristics are observed throughout the channel. Moreover, the findings are generalized via friction factor and Nusselt number correlations, along with an analytical 20-pitch passage model. SR~3.5 is observed to provide favorable characteristics of pitch-to-pitch uniform suction ratio, lack of hot fluid ingestion and to sustain the highest passage averaged heat transfer.