Solve Incompressible Flow Over Converging Duct Oscillating Velocity

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    Fluid Mechanic
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Discussion Overview

The discussion revolves around determining the outlet velocity of an incompressible flow over a converging duct when the inlet velocity is time-dependent, specifically oscillating. Participants explore the applicability of the mass continuity equation in this context, considering the assumptions of incompressibility and inviscidity.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant states that the outlet velocity can be determined using the mass continuity equation, v1A1=v2A2, under the assumption of incompressible flow.
  • Another participant asserts that continuity holds even with a time-dependent inlet velocity.
  • A different participant questions whether the continuity equation is applicable for time-dependent inlet flow, recalling that it is typically associated with steady flow and noting a lack of examples in literature.
  • One participant elaborates that for incompressible flow, changes at the inlet are instantaneously reflected at the outlet, reinforcing that the continuity equation should still apply.

Areas of Agreement / Disagreement

Participants generally agree that the continuity equation can be applied to the scenario, but there is some contention regarding its applicability to time-dependent flows, with differing views on the literature's treatment of such cases.

Contextual Notes

There are unresolved questions about the treatment of time-dependent inlet conditions and the assumptions underlying the continuity equation in this context. Participants express uncertainty about the lack of examples in existing literature.

sykiat89
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given an incompressible steady flow over a converging duct, the outlet velocity can be found just by using mass continuity equation, v1A1=v2A2.

However given a time dependent inlet velocity ie. oscillating velocity, how do i get the outlet velocity? assume the flow is incompressible and inviscid. Tried looking for navier-stoke i had no clue what it does.
 
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Continuity still holds even if your inlet is time-dependent.
 
boneh3ad said:
Continuity still holds even if your inlet is time-dependent.

so, the equation, a1v1=a2v2 is applicable unless it is compressible flow? the last i remembered it is only for steady flow, and non of the books has a worked example for time-dependent inlet flow.
 
If the flow is incompressible then that implies instantaneous "information" propagation. That is, any changes at the inlet will be immediately felt at the outlet.

Basically if you draw a control volume everything, since there can be no accumulation inside the CV due to incompressibility, then any changes at the inlet are immediately felt at the outlet.

So, yes, you're simple continuity equation should hold.
 

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