This paper presents an experimental investigation on the flow characteristics within an entire coolant channel of a 2nd stage high pressure (HP) static turbine blade using TRPIV (Time-Resolution Particle Image Velocimetry) technique. The serpentine channel with three passages connected by a sharp bend, a round bend, 2 tip exits, 8 tailing exits and 40 film-holes staggered arranged on pressure side (PS) of the third pass is chosen as specimen, whose cross sections are manufactured to keep the real blade-shape. Ribs with a fixed spacing-to-height of 7 and an angle of 60° to the flow direction are applied on two opposite walls. The experiment is carried out at a fixed inlet Reynolds number of Rein = 23508. The variation process of secondary vortices and the main flow patterns in typical planes of the realistic coolant channel are successfully captured by TRPIV technique. The effects of rib, bend, cross-sectional shape, layout of passages, ejection ratio on the flow characteristics are analyzed and discussed. The following five new phenomena can be obtained. Namely, 1) near the two bend-regions, the rib can reduce the size of separation bubble and generate a new flow-acceleration downstream of the rib. 2) The rib-vortices combined with the mixing vortex caused by the bend and layout of channels, which leads to a new pair of vortices downstream of the bend, and further downstream, in the pair of vortices, the larger vortex presses the smaller vortex to form a new large vortex. This phenomenon has not been captured up to now in simplified ribbed two-pass channels and smooth realistic channels. 3)The development process of the secondary vortices and asymmetric behavior of main flow structure are similar in the regions of the sharp and round bends. 4)The coolant ejection from the tip exit in the sharp bend can decrease the mixing speed of the secondary vortices downstream of the bend. 5)The tip ejection from the trailing edge exits and film holes can reduce of the size of the secondary vortices downstream of the bend.
Experimental investigation on streamlines in a 180º sharp bend
