The document describes how ANSYS Discovery Live was used to optimize a pipe section in a power plant that was experiencing unstable and recirculating flow. The pipe section was prone to flow-induced vibrations and had a high pressure drop of 406 Pa. ANSYS Discovery Live was able to quickly test different configurations of guiding vanes on-the-fly to both reduce vibrations and lower the pressure drop. The optimized design of 2 inlet and 1 outlet guiding vane stabilized the flow and reduced the pressure drop to 225 Pa, saving the customer thousands in investment and operation costs.

1. Eliminating Flow–Instabilities and Reducing Pressure Drop
in a Pipe Section of a Power Unit
using ANSYS Discovery Live
Dimitris Sofialidis, PhD
Chief Technology Officer

2. Agenda
• Description of the CFD Project.
• Appearance of the problem.
• Need for a quick optimization.
• ANSYS Discovery Live "took the job".
• Demo.
• ANSYS Fluent Validation.
• Conclusions.

3. Description of the CFD Project
• Flow of flue gases in ductwork downstream boilers towards cleaning treatment in absorber.
• Two ductwork branches are the subject of the CFD project; before and after the booster fan.

4. Appearance of the Problem
• The "small duct" section is prone to Flow–Induced Vibrations (FIV), due to highly unstable and recirculating flow.
• The simulation was run in transient solver due to flow instabilities.
• Pressure drop (including dynamic head) was calculated to 406 [Pa].
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Pst,in[Pa]
Time [s]
Mean=81.33 [Pa]

5. Need for a Quick Optimization
• The standard solution for unstable flows in bends and turns is to use Guiding Vanes.
• The GVs achieve in both:
(a) reduce the space available for the vortices and
(b) straighten the flow,
therefore provide a means to:
(a) reduce flow–induced vibrations and
(b) reduce pressure losses due to recirculations.
• The (small) drawback is that they increase the friction losses (additional surface area).
• The questions are:
− How many GVs to use?
− Put both at inlet and outlet bend?
− where exactly to position them?
• If we only had a tool that can answer these questions on–the–fly…
• Well, we have it! It’s ANSYS Discovery Live.

6. ANSYS Discovery Live "took the job".

7. Demo

8. New Design Suggested by DL
1. Starting with 2+2 GV configuration.
2. Finished with 2+1 GV configuration.
After many on-the-fly trials,
the number, location and
orientation of the GVs was
determined.

9. 10
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Pst,in[Pa]
Time [s]
Validation with ANSYS Fluent
• The instabilities dissappeared and simulation was successfully run in steady–state mode.
• Pressure drop (including dynamic head) was reduced to 225 [Pa].
STEADY STATE achieved!

10. Conclusions
• A design/optimization question was raised during a real project in a new power station
under construction.
• A quick decision was necessary to resolve a possible FIV issue in the ductwork.
• New product ANSYS Discovery Live was employed and provided on–the–fly insight and
qualitative optimization trends in a few hours.
• The improved design was validated in ANSYS Fluent and was confirmed that eliminates
flow instabilities but also reduces booster fan power by 2 [mbars], translated into
savings for customer (investment and operation cost) of thousands EUROS.