Measurement and Computation of Flowfield in Transonic Turbine Nozzle Blading With Blunt Trailing Edges

Abstract

Experimental and computational results are presented from cascade testing on the nozzle blading of a high pressure ratio single stage turbine. Testing on this blading in 1986 showed surprising evidence of a redistribution of the downstream total temperature field. The nozzle midspan section has subsequently been tested in a large scale low aspect ratio planar cascade, having a continuous room-temperature inlet flow, to obtain more detailed information over the subsonic and transonic speed ranges. The blades had a blunt trailing edge which caused strong von Ka´rma´n vortex shedding throughout the subsonic range. This was shown to result in Eckert-Weise effect temperature redistribution. The first time-resolved measurements of this effect were measured in this cascade. Unusual vortex configurations were also observed at transonic speeds. The purpose of the current observations was to obtain reliable time-averaged measurements of flow through the cascade, which is proving to be an excellent vehicle for validating CFD predictions. A three-hole finger probe was traversed at the inlet and outlet of the cascade to evaluate the aerodynamic performance. Mach number and base pressure distributions, together with schlieren and surface oil-flow visualization, aided understanding of flow and loss behavior. Two-dimensional numerical simulations were performed over the speed range. The results assisted understanding of the influence of Mach number on losses and flow structures, specifically the shock configurations and base pressures. Comparisons of numerical results and experimental measurements of the flow-field showed good agreement.

Experimental and Numerical Study of Transonic Cooled Turbine Blades

“…In Cascade 2 the base pressure coefficient Figure 12. The Mach number distribution for Cascade 1 in Figure 12a corresponds to the one published in [25]. The rapid acceleration on the front suction side is followed by a strong deceleration in the throat region before reaccelerating smoothly further downstream.…”

“…The increase of the unguided turning angle to δ = 8° in Cascade 2 leads to a flattening of the deceleration zone on the suction surface. In Cascade 2 the base pressure coefficient Figure 12a corresponds to the one published in [25]. The rapid acceleration on the front suction side is followed by a strong deceleration in the throat region before reaccelerating smoothly further downstream.…”

“…Based on this observation and the experimental and numerical results discussed in previous sections, the authors performed loss optimization using the unguided turning angle as a control parameter. The vane with thick and blunt trailing edge investigated in [25] was taken as a reference. The main geometric parameters of this vane are presented in Table 3.…”

“…Many researchers investigated the trailing edge losses without cooling air injection (e.g., [1][2][3][4]6,[14][15][16][17][18][19][20][21][22][23][24][25][26][27]). Basically, these studies show that the direct way of trailing edge loss reduction is the application of thin trailing edges, which may be not applicable to the cooled blades.…”

Organized Streamwise Vorticity on Convex Surfaces With Particular Reference to Turbine Blades

“…This tailboard has proved most effective in reducing undesirable reflections in the downstream flow field. Bypass flaps and tailboards were adjusted to ensure inlet flow uniformity and outlet flow periodicity for each operating condition 18 Figure 3 summarizes the geometry of the cascade and shows the inlet and outlet measuring planes. An important feature was that the blades had a circular trailing edge with a diameter of 6.1 mm.…”