OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
passage vortex. This passage vortex strengthens the counter vortex. Different experiments were performed by
Marchal et al. [2], Sieverding et al. [3], Wang et al. [4] and Sharma et al. [5] which confirmed the conclusions of
Langston et al. [1]. Later on experiments were performed for reducing the secondary loss. In the literature two
methods were proposed for secondary loss reduction. One is leading edge modification and other is end wall
contouring. There are two main designs for leading edge modification is: the fillet and the bulb. Young J. Moon et al.
[6] analyzed the effect of end wall fencing for reducing the secondary flow using k-ξ turbulence model. They also
justified the optimized positioning of the endwall fencing for reducing the secondary flow losses, because the end
wall fencing prevents the merging of pressure side horse shoe vortex with the passage vortex and hence total pressure
loss decreases. Arun K. Saha et al. [7] analyzed the turbulent flow through a three dimensional non-axisymmetrical
blade passage and observed that endwall contouring reduces the pitchwise pressure gradient near the endwall which
reduces the chances of flow separation. Toyotaka Sonoda et al. [8] use axisymmetrical end wall contouring method
for reducing the secondary losses in high pressure turbine having low aspect ratio. Brear et al. in [9] tried to reduce
this pressure surface separation by modifying the leading edge geometry. They concluded that increasing the blade
thickness at the pressure surface decrease the strength of secondary flow by increasing the momentum near the wall.
Shih et al. [10] observed effects of leading-edge airfoil fillet on the flow in a turbine. The increased size of the
stagnation zones on the endwalls about the airfoil’s leading edge lowers the flow speed and velocity gradients there,
which in turns reduces turbulence production. G. I. Mahmood et al. [11] studied the secondary structure in a blade
passage with and without leading edge fillet and observed that the size and strength of the passage vortex become
smaller with the fillets. T. Korakianitis et al. [12] has proposed a direct design method based on specifying blade
surface-curvature distributions so as to minimize the chances of flow separation. Qi Lei et al. [13] analyzed the effect
of leading edge modification on the secondary loss. They used vortex generator for introducing counter rotating
vortex which oppose the passage vortex and hence reduce the secondary flow losses.
Much work has been done to understand the occurrence and modeling of secondary flow and end loss phenomenon.
Moreover researchers had tried to reduce the secondary loss in any cascade in order to get higher aerodynamic efficiency
of the power plant. It is a well known fact that roughness over the blade surface increases the profile loss in the cascade.
But effect of roughness on the secondary flow and corresponding losses has not studied much. The secondary loss in
smooth cascade has been compared with the secondary loss in the cascade having rough surface. This work is done in
order to find out the effect of roughness present on the blade surfaces of the turbine cascade on the secondary loss
2. Modeling
The present computational study has been carried out using Computational Fluid Dynamics (CFD). The brief of CFD
software used and description of problem and boundary conditions is presented here.
2.1 CFD simulation
CFD is a computational technology that uses numerical methods and algorithms to solve and analyze problems that
enables us to study the dynamics of flow. CFD uses numerical methods to solve the fundamental nonlinear
differential equations that describe fluid flow (the Navier-Stokes and allied equations), for predefined
geometries and boundary conditions.
Using CFD, one can build geometry and provide proper boundary conditions representing the virtual prototype
and then the computational software predicts the fluid dynamics and performance of the prototype. Three-dimensional
model of 6030 cascade geometry has been made with the help of Gambit® 2.2.3 as pre processor & FLUENT® 6.2 is
used as solver & post processor for flow simulation. Theoretically, to analyze the fluid flow, the basic
conservation equations have to be solved.
a) Conservation of momentum (Navier-Stokes equation)
∂ ∂
∂p
∂τ
ij
( ρ u
i
) + ( ρu
iu
j
) = − + + ρg
i
+ Fi
(2.1)
∂t
∂x
∂x
∂x
b) Conservation of mass (Continuity equation)
∂ρ
+
∂
i m
∂t
∂xi
c) Conservation of energy (Energy Equation)
j
(ρu
) = S
j
j
(2.2)
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