| Modifications to both laminar and turbulent approach juncture flows due to the presence of a clearance gap were examined in a low-speed water channel using particle imaging velocimetry and a thermochromic liquid crystal heat transfer measurement technique. When a clearance gap is present, a layer of outer region fluid diverts downward along the juncture body, creating a saddle point on the endwall. From the saddle point, a portion of the impinging flow moves upstream, and the remaining portion flows directly into the clearance gap. Necklace (laminar) and horseshoe (turbulent)juncture vortices, typical of juncture flows without gaps, continue to form upstream of this endwall saddle point, until the gap clearance exceeds h/D ≈20% for a laminar flow or ≈10% for a turbulent flow. The location of the endwall saddle point moves upstream with increasing gap thickness. When a significant gap clearance is present, the primary vortex for both the laminar and turbulent approach juncture flows is cyclically swept (ingested) into the clearance gap.; For a turbulent approach juncture flow, a four-stage cycle was identified, consisting of: (1) vorticity organization; (2) development of a quasi-steady horseshoe vortex; (3) vortex weakening; (4) vortex ingestion. Coherent regions of negative vorticity, advected within the boundary layer, amalgamate with, and maintain the strength of, the horseshoe vortex. As the clearance gap increases, fewer negative vorticity regions amalgamate with the horseshoe vortex, which causes the vortex to weaken, and exhibit longer organization times and less organized behavior.; The presence of a clearance gap in a juncture flow results in several modifications to the endwall surface heat transfer, including: (1) an increase of roughly 25% in the local peak surface heat transfer, (2) a reduction in the extent of the endwall region which experiences elevated surface heat transfer, and (3) a dislocation of the region of highest heat transfer from upstream of the juncture comer to within the leading edge of the clearance gap. |
