## Effect of Film Cooling Hole Size on a Turbine Rotor Blade

##### Abstract

The objective of this study was to evaluate the effect of the cooling hole size on
the adiabatic film cooling effectiveness over a rotating turbine blade section. The
study was conducted using ANSYS FLUENT to determine the adiabatic wall
temperature over the blade surface. The geometry was created to be a single
section of a turbine rotating at 4000 rpm, and the blade increases in camber from
tip to hub. Cylindrical cooling holes were created and the diameters were varied
from 0.5 mm to 1.5 mm. The pitch-to-diameter ratio and the length-to-diameter
ratio were kept constant at a value of 3. An unstructured mesh was generated for
the geometry, and an inflation layer was created to capture the boundary layer
around the blade surface. The Shear-Stress Transport k-ω turbulent model was
used with the curvature correction and production limiter. The velocity
boundary condition for the flow entering the domain was set such that the angle
with respect to axial direction was the same as the angle-of-attack of the blade.
Therefore, the velocity components in the y−direction and the z−direction were
set to values of -128.56 m/s and 153.21 m/s, respectively, and the temperature
was set such that T The objective of this study was to evaluate the effect of the cooling hole size on
the adiabatic film cooling effectiveness over a rotating turbine blade section. The
study was conducted using ANSYS FLUENT to determine the adiabatic wall
temperature over the blade surface. The geometry was created to be a single
section of a turbine rotating at 4000 rpm, and the blade increases in camber from
tip to hub. Cylindrical cooling holes were created and the diameters were varied
from 0.5 mm to 1.5 mm. The pitch-to-diameter ratio and the length-to-diameter
ratio were kept constant at a value of 3. An unstructured mesh was generated for
the geometry, and an inflation layer was created to capture the boundary layer
around the blade surface. The Shear-Stress Transport k-ω turbulent model was
used with the curvature correction and production limiter. The velocity
boundary condition for the flow entering the domain was set such that the angle
with respect to axial direction was the same as the angle-of-attack of the blade.
Therefore, the velocity components in the y−direction and the z−direction were
set to values of -128.56 m/s and 153.21 m/s, respectively, and the temperature
was set such that T∞ = 1800 K. The velocity boundary conditions at the hole
inlets were calculated such that the mass flow rates on the suction and pressure
= 1800 K. The velocity boundary conditions at the hole
inlets were calculated such that the mass flow rates on the suction and pressure sides were 0.00384 kg/s and 0.01295 kg/s, respectively. The temperature
boundary condition at the hole inlets was calculated to be 973.86 K. A
quantitative analysis was performed using the exported temperature data, where
the laterally-averaged effectiveness was plotted against the non-dimensional
position, z/c. Qualitative analysis was also performed by observing the
temperature distributions on the blade surface, as well as the velocity streamlines
from the inlets of the film cooling holes. Streamlines colored by Mach number
were used to ensure flow remained subsonic. Based on the results, the increase in
the hole size improved the distribution of the effectiveness downstream from the
holes on the pressure side, but had minimal effect on the effectiveness on the
suction side. An increase in the cooling hole size caused an increase in the
spreading of the coolant from the cooling hole exits over the blade surface. On
the pressure side, the slope on the effectiveness plots for the larger angles show
that the amount of cooling remains almost the same along the blade’s axial
position.