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Maxim Pisarenco
| Speaker: |
Maxim Pisarenco
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| Date: |
Friday August 14, 2007
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| Title: |
Friction Factor
Estimation for Turbulent Flow in Corrugated Pipes with
Rough Walls (Master's Thesis Presentation)
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Abstract
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Non-metallic
flexible pipes are widely used in industry. They are comprised of
fabric wrapped over a spiral metal framework. Due to this construction,
they respond very well to bending and they are cheaper and much easier
to install than metal pipes. Because of the specific construction, the
pipe walls are corrugated and the fabric which covers the steel spiral
is much rougher than the wall of a metal pipe. In this investigation we
are interested in estimating the friction factor for the flow in this
type of pipes.
Two-equation turbulence models (k−ε and k−ω) are used in the
computations. The process of deriving these models is briefly presented
first. Then we look at the law of the wall (which gives the velocity
profile near the wall) and its use as a boundary condition is explained.
After the theoretical ideas have been exposed, we look at fully
developed turbulent flow in a conventional pipe. Simulations are
performed to validate the chosen models, boundary conditions and
computational grids. Then a new boundary condition is implemented based
on the ”combined” law of the wall. It enables us to model the effects
of roughness. The new boundary condition is validated by performing
simulations of turbulent flow in rough pipes and comparing the computed
friction factor to the one given by the Moody diagram.
Finally, turbulent flow in periodically corrugated (flexible) pipes is
considered. New flow phenomena (such as flow separation) caused by the
corrugation are pointed out and the essence of periodically fully
developed flow is explained. The friction factor for different values
of relative roughness of the fabric is estimated by performing a series
of simulations. Conclusions are drawn based on the results of the
computations. Some of them are that the k−ε model performs slightly
better than the k−ω model in predicting both regular and separated flow
and that the friction factor in a flexible corrugated pipe is mostly
determined by the shape and size of the steel spiral, and not by the
type of the fabric which is wrapped around the spiral.
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