0
$\begingroup$

I'm interested in the resistance a body feels as it travels through a static fluid in a tube (of a fixed radius), at different pressures.

I would assume that as the pressure is reduced, the resistance will also be decreased. Does this relate to the Drag Force equation, or is there a better explanation, such as Bernoulli?

$\endgroup$
2
  • $\begingroup$ I think it would end up being a lot more complicated than "more pressure = more resistance". Pressure will effect the flow, which will change the way the turbulence interacts with the object. Consider that for any closed surface in a pressurized fluid, the pressure acts in every direction. You may wind up with a lot of edge cases where the effects of changing pressure react with turbulence in unexpected ways. $\endgroup$
    – JMac
    Aug 8, 2018 at 16:04
  • $\begingroup$ If the fluid is essentially incompressible, the absolute level of the pressure will not affect the drag force. Only spatial pressure and stress variations will accept it. $\endgroup$ Aug 8, 2018 at 17:40

1 Answer 1

2
$\begingroup$

As mentioned in one of the comments, if the fluid is incompressible (i.e. - has constant density) then the absolute level of the pressure will not affect the drag.

However if the fluid is a gas, then the pressure and density will be strongly related (directly proportional for ideal gases). And the density of the fluid enters into the equation for the dynamic pressure, so it does affect the drag.

For a constant drag coefficient, the drag will be directly proportional to the density, so for streamlined shapes at sufficiently large Reynolds' numbers, the drag will be approximately proportional to the pressure.

This should be true even if the Mach number of the flow is small enough for the incompressible flow equations to be used.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.