LPT CFD

1. ABSTRACT
Low pressure turbine (LPT) is the vital component in modern turbofan engines. In modern
turbofan engines Fan produces major thrust and which is run by LPT. It is estimated that 1%
increase in efficiency of LPT translates into ~1% increase in overall engine efficiency. The
goal of LPT designer is to increase the torque or loading of turbine, which in turns can be
used to reduce no of blades for decreasing weight or to increase the thrust from the given fuel
consumption.
LP turbine are affected by adverse pressure gradient when loading is increased beyond
certain limit and Reynolds number is less than critical one. Due to the adverse pressure
gradient, separation is generated at the suction side of the blade. The more the loading, the
higher the separation is felt on the blade. The loading is defined by the Zweifel coefficient,
which is 0.88 for T106a blade.
There are two methods to control the separation: Active and passive control. Both methods
have advantages and disadvantages. They suffer from the complex mechanism, losses at
higher Reynolds number, manufacturing difficulty and additional cost.
It is also observed that the incoming wakes from upstream components also reduce the
separation but they tend to be ineffective i) due to excessively low Reynolds especially in
case of higher loading LP turbines ii) Due to almost half no of blades in NGV where wakes
are effective for half of the time.
Keeping in view the above discussion i.e. the separation control mechanism (using passive
and active control) and effect of incoming wakes, we propose to study the different wakes
from differ type of trailing edges of NGV in generic way. Here we have varied by stretching
and compressing of non-dimensional wake profile from the cylinder of 2.2 mm thickness
(from Steiger’s PhD Thesis at Cambridge University). Wake is modelled as non-dimensional
Gaussian profile and is implemented using UDF in Ansys Fluent. Mesh was generated in
Gambit. Mesh independence study was made and finally we chose the very fine mesh with
112,000 no of nodes.
First we have validated our study at inlet Reynolds number of 91000 by comparing our
approach with precursor simulation with meshed cylinder. Our results agree very well with
with precursor simulation of meshed cylinder and with Steigers’s experimental results as
well. Results of the complete study shall be presented in full length paper.