RESULTS AND
DISCUSSIONS
In this section, results from ANSYS simulations of the eight operating
speeds are manifested. First, the results are displayed in the form of
validation and verification performed in 2D; it is then followed by a
detailed analysis of the 3d simulation of the blade. Herein, simulation
has been accomplished by considering the 1200 sector
of the turbine rotor.
2d simulation of flow around S809
airfoil
S809 airfoil has been selected as an airfoil from the NREL phase VI
Blade to benchmark the numerical framework. The simulations are
accomplished under the static condition at the velocity of 3.65 m/s,
7.30 m/s, 14.60 m/s,21.91m/s and multiple angles of attack. The pressure
and velocity contour of S809 airfoil are shown in figure 13. It
demonstrates that as the airflow above and below the surface of an
airfoil, the formation of a starting vortex behind the airfoil near the
wake expansion zone is initiated. This starting vortex rotates in a
counter-clockwise direction and to maintain the conservation of angular
momentum, another motion opposite to the motion of starting vortex needs
to be generated, which further leads to the formation of circulation
around the airfoil. The velocity vector that formed due to circulation
adds to the free stream velocity vectors, thus resulting in a higher
velocity above the airfoil and lower velocity below the airfoil.
Considering this variation and implementing Bernoulli’s equations, the
pressure difference can be opted out from the surfaces of the airfoil.
Due to the pressure differences, there is higher pressure at the lower
surface of the airfoil and lower pressure at the upper surface of the
airfoil and this eventually leads to the generation of the lift.
In figure 13, every color tone has some meaningful significance. Here
red color tone signifies maximum value, whereas dark value signifies the
least. Green color and yellow tone maintain the optimized range. Here in
figure 13, the upper part portrays velocity contour and the lower one
reflects pressure contour. In the velocity contour, at the leading edge
of the airfoil and velocity near to the surface of the airfoil is very
less due to stagnation point and due to this, colour tone here is blue
which is reflecting less value. When moving slowly away from the airfoil
surface the colour tone also changes gradually until it reaches 0.99
free stream velocity (boundary layer thickness zone).
Figure 14 through figure 19, illustrates the validation of numerical
aerodynamic results against the experimental benchmark data. The results
of aerodynamic coefficients from CFD portrayed in good agreement with
the benchmark data. In figure 14 and figure 15 plotting of coefficient
of lift and drag obtained from numerical simulations is highlighted. In
figure 16 and figure 18, both experimental results Show discrepant at
AOA>=150. An error of 3% to 6% between
CFD and experimental results comes when performed at Reynolds’s number
1E6 at AOA<170 shown in figure 16 and figure
18. However, when the angle of attack increases, the drag coefficient of
the DUT experiment [37] shows inconsistent behaviour, whereas OSU
experimental results [38] especially lift and pressure drag, become
more reasonable. Moreover, in figure 17 and figure 19, numerical results
obtained from CFD calculation are in good agreement with CSU
Experimental results [39] performed at Reynolds
number\(\ 5\times 10^{5}\).An average error of less than 6% comes
after comparing the results.
In general, a close agreement demonstrates the correct design strategy
and the appropriate choice of the boundary condition on the domain. The
estimation of Aerodynamic coefficients should be reliable as it is
directly related to the contribution of torque in generating lift
produced
From the blade. The trend of lift coefficient is such that it first
increases with an increase in the angle of attack, reach maximum up to
stall angle, and after that, it starts to drop again. It displays the
exact position of stall around the airfoil and demonstrates the accuracy
of the numerical setup.