The discussion revolves around the concept of steady flow in fluid dynamics, specifically questioning whether a flow considered steady implies that all properties of the flow are also steady, or if it is possible for a flow to exhibit both steady and unsteady properties simultaneously. The scope includes theoretical considerations and practical implications in fluid mechanics.
Participants express differing views on the relationship between steady and unsteady properties in flow. There is no consensus on whether turbulence should be classified as unsteady in a steady-state context, and the discussion remains unresolved regarding the implications of averaging in turbulent flow analysis.
Participants highlight the dependence on time and spatial scales when discussing steady and unsteady properties, indicating that the definitions and interpretations may vary based on specific contexts and applications.
In a steady flow, nothing is changing with time at each spatial location.ltkach2015 said:QUESTION:
In general: when a flow is considered steady does that mean all properties of the flow are steady?
Or: can a flow have steady and unsteady properties?
Is that your professional judgement in addressing practical problems in turbulent flow? In my judgement, it depends on the time- and spatial scale of the averaging. After all, we don't treat individual molecular collisions and vibrations as part of the unsteadiness, even though that can certainly be regarded as unsteadiness on a very short time and spatial scale. In my experience, the time- and spatial scales in typical practical problems involving turbulent flow does not necessitate specifically treating the system as an unsteady flow. Even when studying how turbulence plays out in determining the stresses in a fluid in turbulent flow, the objective is to average out the statistical variations so that the results can be applied at larger time- and spatial scales. This is called the hierarchy approach.insightful said:I would say turbulence in a vessel or pipe could be considered unsteady-state in a steady-state process.
Of course not. The straw man lives!Chestermiller said:Is that your professional judgement in addressing practical problems in turbulent flow?
Sometimes a simple answer, on the level of the question asked by the member, is a better choice than a more complicated intricate response (even if the more complicated response fleshes out the answer in greater detail), in terms of giving the member what he needs. It is often less confusing that way. The member will have plenty of opportunity to study the situation in greater detail as his studies progress in the future. In other words, sometimes less is better.insightful said:Of course not. The straw man lives!