PIPING
CORRUGATED
PIPE
Flow instability and vibration
in stainless steel flexible hose
CLIENT
Manufacturer of compressed-air systems and industrial fluid-dynamic components
CHALLENGE
Find the velocity at which flow instability sets in, and how it relates to flow rate and to the corrugation itself
RESULT
Trigger conditions identified, oscillation frequencies and amplitudes characterised, design guidance delivered
01
CHALLENGE
In service the client’s corrugated hose was showing flow instability and vibration, and with it the risk of components failing earlier than they should.
The corrugated profile is what makes the hose mechanically flexible, and it is also what disturbs the flow: it produces flow separation, complex turbulence and oscillatory phenomena. Traditional analytical methods predict none of this reliably, least of all where the flow arriving at the hose is not uniform or the operating conditions vary.
What the client needed was the critical conditions, quantified — for three sizes of hose: 2½ inch, 3 inch and 4 inch.
02
SOLUTION
We built a CFD model of the flow inside the corrugated hose, run unsteady rather than steady, because a steady simulation cannot see an oscillation.
The hose geometries were reconstructed from the supplier data with the corrugation profile resolved in detail — that detail is the whole mechanism, so simplifying it away would have answered a different question.
Each configuration was then run at several flow rates to follow how the flow develops and to catch the point where instability appears. The campaign covered both simplified configurations, quick enough for a first assessment, and fuller models able to include the effect of disturbed flow upstream of the hose.
03
RESULTS
The simulations characterised the flow inside the corrugated hose in detail. They made it possible to identify the critical velocity above which oscillation begins, to analyse the frequency and amplitude of the resulting vibration, and to understand how the geometry itself governs the stability of the flow.
For the client that turned into concrete guidance: how to reduce the risk of instability, how to improve component reliability, and which way to take the design.
