Conservation of Momentum Question

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Homework Help Overview

The problem involves the conservation of momentum in a fluid dynamics context, specifically analyzing the forces acting on a vane in a 2D flow of an incompressible fluid. The scenario is set between two stations where velocity and pressure are defined, and the angles of flow at each station are given.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the forces acting at two stations, including pressure and momentum forces. There are attempts to clarify the dimensions and assumptions regarding the density and pressure terms. Questions arise about the signs of forces and the implications of incompressibility on the flow.

Discussion Status

The discussion is ongoing with participants providing feedback on each other's reasoning. Some have offered clarifications regarding the equations and the physical interpretation of forces, while others are questioning the assumptions made about the dimensions and the relationships between variables.

Contextual Notes

There are mentions of potential typos in the equations and the need for clearer definitions of terms. The discussion also highlights the importance of understanding the relationship between velocity, pressure, and the geometry of the flow setup.

  • #31
haruspex said:
In the x direction, we know that the volumetric rate of flow into the blade system from the left must equal the flow out on the right. In the y direction there is no requirement that volumetric rate of flow up the left side of the blades must equal that on the right side.
Ok, I think I have it! I wrote up a proof, starting with the momentum equation, assuming incompressible, steady, non-viscous flow and neglecting body forces. I'll attach it since typing it took some time. Let me know what you think, as I have one question with what I wrote.
 

Attachments

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  • #32
joshmccraney said:
Ok, I think I have it! I wrote up a proof, starting with the momentum equation, assuming incompressible, steady, non-viscous flow and neglecting body forces. I'll attach it since typing it took some time. Let me know what you think, as I have one question with what I wrote.
Yes, that all looks correct to me.
 
  • #33
haruspex said:
Yes, that all looks correct to me.
Awesome, thanks so much for your help! I really appreciate it!
 
  • #34
I get the opposite signs than you have obtained for the components of the external force necessary to hold the vane in place.
 
  • #35
Chestermiller said:
I get the opposite signs than you have obtained for the components of the external force necessary to hold the vane in place.
Good point. I read the diagram as indicating Rx and Ry are the forces the flow exerts on the vanes, and did not notice that wording.
 
  • #36
Shoot, thanks! I'll fix this!
 

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