Numerical Investigations on the Effect of Setting Angle Change in Part Clearance Flow Field of Variable Area Lp Turbine Nozzle Vane

The gas turbine engines, use in various applications, operate under off-design conditions for a
considerable time duration. The performance and efficiency of the gas turbine engines
deteriorate under such off-design conditions. The variable area nozzle turbine (VANT) is a
variable geometry concept which can be used to improve the performance of the gas turbine
engine in part-load condition. However, mechanical aspects to implement VANT demands for
part clearances to be provided near the hub and tip endwalls. These part clearances are
responsible for the leakage flow from the pressure surface to the suction surface of the vane
under the pressure gradient. This leakage flow mixes with the primary incoming flow and
affects the overall performance of the gas turbine engine.
2nd stage low-pressure turbine stator of energy efficient engine (EEE) proposed by Pratt and
Whitney was considered for the present study. The available vane profiles and pressure
distribution data at five different spanwise locations were used to construct the vane geometry.
The annular cascade of vane geometry was scaled by factor 1.2 to experimentally investigate
the flow field using sector annular cascade tunnel conditions. The vane ends and both the
endwalls were modified to concentric spherical shape with its center on the engine axis. This
allows constant part clearance during movement of the vane of the VANT application. The
modification was done to accommodate the high casing endwall angle and hence, the rear step
was provided at the upstream of the vane leading edge near the tip. In order to change the
nozzle throat area by changing its stagger angle, the vanes were made free to rotate in the
annular passage. The vanes were held in the hub and casing endwalls by the pivot passing
through it. However, the pivot in the part clearances near hub and tip need to be selected such
that the leakage flow through part clearances and hence losses can be minimized.
For the present study, two pivot shapes, circular and elliptical, in the 2 mm part clearance near
the hub and tip regions were chosen. The present work also incorporates the effect of the pivot
shape on the vane passage flow field at five different vane turning angles from +10º to -10° at
an interval of 5º. This vane turning helps to change the throat area of the nozzle which governs
the air mass flow rate through the engine turbine section. For numerical analysis, the grid was
generated in the ICEM CFD® for nozzle flow passage with pivot shape and numerical study
was performed using commercially available CFD tool ANSYS CFX®.
The effect of different pivot shapes with the change in setting angle of nozzle vane on the
leakage flow, formation of the leakage vortex and its interaction with the main passage flow
were analyzed using entropy, vorticity, and total pressure loss coefficient. Also, the structure
of the leakage flow and hence leakage vortex changes with the change in the vane turning
angle. The poster focusses more on detailed flow field study within the part clearances near the
hub and tip region and flows three dimensionalities within the nozzle passage and exit flow
field.