The Experimental & Computational Convection Laboratory (ExCCL)

The Experimental & Computational Convection Laboratory (ExCCL)


In the Experimental and Computational
Convection Laboratory at Penn State, which is part of the Turbine Heat Transfer and Aerodynamics
Group, we work on fundamental convective heat transfer issues in gas turbine engines.
In a gas turbine engine, air flows first through the fan, next the compressor, next the combustor,
through the turbine, and then out the exit. Where we work is in the turbine area, where
the environment is extremely hostile due to the high temperature gases that flows over
all components. For internal cooling in turbine engine blades,
blades are generally hollowed out as you can see in this image here, to provide cooling
from the internal channels. The cooling in the internal channels usually is turbulated
by some type of features inside the blade, as you can see here, as well as features that
are located within the trailing edge of the blade, such as small pin fin arrays that span
the pressure and suction side of the airfoil. The work that I do is in a large scale optically
accessible pin fin rig, and I work with particle image velocimetry. Essentially you have a
laser that illuminates particles within a flow field and you use a high speed camera
to capture these particles which you can then translate into a complete three-dimensional
vector field. On the airfoil surface, small holes are drilled
into the metal and coolant is pumped through those holes to provide a film of cold air
that protects the metal from hot gas-path temperatures. My research in the ExCCL lab is on film cooling. So film cooling holes have a cylindrical metering
section with a larger diffuser on the end, and in our rig we can test multiple complicated
geometries of these film cooling holes and vary some parameters of the diffuser in order
to get better film cooling effectiveness. Then we can take pictures of the endwall with
an IR camera to get pictures like this that show the temperature of the wall, so we can
see how effective each film cooling hole is. One way to measure the velocities in film
cooling flows is called laser Doppler velocimetry, which is a system we have in our lab. Basically,
you take one or more laser beams and you cross them together at a single point, and at that point you can get the velocity, because we seed our flow with very small particles, and whenever
a particle goes through this intersection point, because of the interference pattern
set up a series of flashes occurs, and the measurement system can relate how fast the
flashes occur to how fast the particle moves, and you can get, depending on all the laser
beams, you can get all three components of velocity at that point.
In a gas turbine engine, multiple parts such as these are assembled into a full wheel to
make the entire turbine. Gaps between individual components are purged with cold air, which
can interact with the main gas path flow, and create disturbances in that flow path.
The complicated flow in the gas turbine engine around the airfoil can result in high metal
temperatures. We have the facilities of a large scale recirculating
wind tunnel. We take scaled engine relevant hardware and are able to take test measurements
and use diagnostic tools that just wouldn’92t be possible in an actual engine. On my rig,
we use particle image velocimetry to get flow field data in otherwise hard to reach areas
of an engine. The large scale wind tunnel allows us to generate
the complex flow structures that affect gas turbine heat transfer. My project uses a novel
method to consider the combined effects of the external heat transfer and internal cooling.
The scaled temperatures that I measure are directly applicable to the engine, so it has
been exciting to work on a project so relevant to the gas turbine community.
As a grad student in the ExCCL lab, we study engine relevant problems using state of the
art technologies. For example, we use IR thermography to map the temperature on the endwall surface
of a turbine. We’re looking at the mixing of the cold purge flows with the hot main
gas path. And we use laser diagnostics to measure the velocities fields in those trench
regions to explain the mixing that we see. Using state of the art technologies to study
these industry relevant problems has helped prepare me for a successful career in the
gas turbine industry.

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