Effects of squealer rim height on heat/mass transfer on the floor of cavity squealer tip in a high turning turbine blade cascade

The effects of hst/s (squealer rim height-to-span ratio) on heat/mass transfer rate on the floor of the cavity squealer tip have been investigated in a high turning turbine blade cascade by employing the naphthalene sublimation technique along with oil film flow visualizations. Tested squealer rim heights are hst/s = 0.00% (plane tip), 0.94%, 1.88%, 3.75%, and 5.63% for a tip gap height-to-span ratio of h/s = 1.02%. For comparison purpose, the tip gap height is changed from h/s = 0.34% to 1.70% for hst/s = 3.75%. Heat/mass transfer rate on the cavity floor upstream of the mid-chord is affected by the leading edge tip gap vortices as well as by the reattachment of the incoming tip leakage flow to the cavity floor for lower hst/s, as in the plane tip case, whereas it is influenced mainly by the impingement of the incoming tip leakage flow onto the cavity floor near the leading edge for higher hst/s. On the other hand, heat/mass transfer rate downstream of the mid-chord is determined by the downwash flow which is entrapped by the suction-side squealer rim. With increasing hst/s, average heat/mass transfer rate on the cavity floor decreases steeply at first and then decreases mildly in the same manner as over-tip leakage loss. Average heat/mass transfer rate on the cavity floor is more sensitive to the squealer rim height than to the tip gap height.