Physics Help Forum Compressible vs. Incompressible flow

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

 Dec 27th 2018, 10:40 AM #1 Junior Member   Join Date: Dec 2018 Posts: 1 Compressible vs. Incompressible flow Hello dears, I have seen many explanations in various references about the definition of compressible flow. In fact, changing the density of the flow as a result of pressure variations leads to a compressible flow. Now, my question is that what if the density of the fluid flow changes as a result of temperature changes which come from heat transfer on boundaries. Imagine a situation in which the fluid flow density is changing by temperature but the Mach number is low. Is it a compressible or incompressible flow? Best Regards
 Dec 28th 2018, 11:44 AM #2 Senior Member     Join Date: Jun 2016 Location: England Posts: 1,011 Incompressible flow is always an approximation, However it is far easier to model incompressible flow than compressible. The question becomes, are the flow conditions close enough to incompressible for the simpler model to be used as an acceptable approximation. If the fluid has a thermocline, or similar boundary, you may be able to assume incompressible conditions on either side of the boundary, but you would have to make special provision in any model for the boundary. topsquark likes this. __________________ ~\o/~
 Dec 29th 2018, 08:28 AM #3 Member     Join Date: Sep 2014 Location: Brasília, DF - Brazil Posts: 32 Some points... Incompressible fluid is a material property Incompressible flow describes a flow property Pont 1 - In an incompressible flow, the density of a fluid element doesn't change along its pathline. So you can have an incompressible flow of compressible fluid in the case of low Mach numbers or in stratified flows. Point 2 - An incompressible fluid always results in an incompressible flow topsquark likes this. __________________ Work on: General thermal systems Cryogenics Micro-drop fluid mechanics
 Mar 6th 2019, 01:59 AM #4 Junior Member   Join Date: Mar 2019 Posts: 5 When a fluid flow is compressible, the fluid density varies with its pressure. Compressible flows are usually high speed flows with Mach numbers greater than about 0.3. Examples include aerodynamic applications such as flow over a wing or aircraft nacelle as well as industrial applications such as flow through high-performance valves. Incompressible flows do not have such a variation of density. The key differentiation between compressible and incompressible is the velocity of the flow. A fluid such as air that is moving slower than Mach 0.3 is considered incompressible, even though it is a gas. A gas that is run through a compressor is not truly considered compressible (in the thermodynamic sense) unless its velocity exceeds Mach 0.3. This is important to note because analyses run as compressible can be harder to run, and require more longer analysis times than incompressible flows.

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post clone477 Thermodynamics and Fluid Mechanics 7 Mar 28th 2018 07:33 PM studiot Thermodynamics and Fluid Mechanics 1 Feb 9th 2018 08:07 AM Rocco30 Thermodynamics and Fluid Mechanics 0 Mar 16th 2016 03:58 PM arpitv7 Thermodynamics and Fluid Mechanics 6 Aug 10th 2015 03:03 PM Devlan Advanced Mechanics 2 Jun 2nd 2014 01:20 PM