Let's say that there is a empty bottle in the water moving at a high speed like this: enter image description here

My question is: Will the water go inside the the empty bottle when the bottle is moving at a high speed? If yes, from what this speed is affected? and if this bottle is 1/2 full will its water come out? Thanks in advance.

  • $\begingroup$ My first guess to this is that the answer to this question is going to depend pretty sensitively on the shape and size of the nozzle. $\endgroup$ Jul 15, 2015 at 14:00

2 Answers 2


The opening sees water at stagnation pressure. Water will flow in until the air in the bottle is squeezed to that pressure.

  • $\begingroup$ +1 - and/but I think interesting things happen when the opening is mid level as it is, with the ability to exchange water and air at ~= equal pressures. Small orifices may have interesting second order effects (surface tension, ...) but I think sensibly large holes (say ?5%? of dia on up? ) may lead to the bottle filling to about the top of the hole over time regardless of speed at "sensible" speeds. Yes? No? Other? $\endgroup$ Jul 15, 2015 at 14:15
  • $\begingroup$ @Russell: The issue is: where does the air go? Sure, once there is pressure equilibrium at the orifice, stuff can flow out and in at the same time, as long as the net volumetric flow is zero. $\endgroup$ Jul 15, 2015 at 14:27
  • $\begingroup$ Thanks for the answer, but I was thiking that if this bottle is a wine bottle maybe at a high speed the drag force which is causing this phenomenon link_here can push the water which is at the nozzle so as not to get inside the bottle. Of course we are assuming that the bottle is moving at the direction of the bottom as shown at the question's picture. Are my thoughts correct? $\endgroup$
    – Oluderi
    Jul 15, 2015 at 16:04
  • $\begingroup$ @Vaggelis: Forget drag. Suppose the water is flowing and the bottle is stationary. Then the water outside the mouth of the bottle has to come to a stop. In order to do that, some pressure has to stop it, and that is the stagnation pressure. Then, you get into questions of how big is the nozzle, can some more water flow in while some water/air flows out, etc. That's a different question, depending on how big the nozzle is, and so on. $\endgroup$ Jul 15, 2015 at 16:45

I'm appreciating your thinking and question.

This question will be even more challenging question if the working fluid is air instead of water and fluid is moving. In this answer I'm considering bottle is moving and fluid is moving in opposite direction of bottle. (because stationary fluid is sub case of moving fluid where $v_1$=0)

Let us assume the the bottle is empty and moving from zero velocity to a constant velocity, because of relative motion between bottle and fluid ( here I'm considering air because compressibility of air is more than water, fluid will enter the bottle at the mass flow rate $$\dot{m} = c_d \rho A_{c} v_1$$ here $c_d$ is discharge coefficient depends on lid design of bottle.

$\rho, A_{c}$ and $v_1$ are density of fluid, cross sectional area normal to flow angle and relative Velocity of external fluid and bottle respectively. If there is a contraction then we should use continuity equation

$\rho_{1} A_1 v_1=\rho_{2} A_2 v_2$

here $_2$ is properties after diverging section and $_1$ is free steam properties.

This is valid till the flow touches the other end of bottle. After that this continuity equation is not valid because no mass flow rate outside of bottle. Then the velocity inside the bottle can be calculated from Bernoulli equation. please note that till I'm in incompressible region of flow and that velocity is calculated from,

$v_2= \sqrt[]{\frac{2*(p_1-p_2)}{\rho_1}}+v_1$

One that fluid hit the end of the bottle, "hammer effect" (similar to "water hammer effect") will take place and one shock will move from end of bottle to lid of the bottle at about the speed of sound in incompressible region and more than that in compressible region. This shock will increase the pressure of the fluid inside the bottle and reduces the previous inflow velocity calculated from continuity. This shock also makes the velocity of fluid behind the shock, zero. Please refer the following link to get an idea how to calculate the flow properties in moving shock. This is a dynamic process, this shock will tell information to the upstream fluid that "there is a wall so we can't move". After the pressure inside the bottle reaches stagnation pressure every where (flow become quasi-steady state) the fluid layer at the lid of bottle act like a solid wall and it will not allow further new fluid elements to go into the bottle.

Will the fluid inside the bottle go out?

  • We may think stagnation of pressure is more than the external pressure so fluid may come out but the possibility is less because. Next layer outside the fluid lid is stagnated because of solid nature of fluid layer in lid ( already mentioned), so leakage is impossible unless some complex process takes place.

  • That reflected shock from the bottle end will from a normal shock in front of the bottle and reduce the velocity of fluid entering the bottle. Because of that reflected shock a factious layer of the immobile fluid layer (w.r.t bottle) that covers the bottle where pressure is less than or equal to the stagnation pressure of external fluid so fluid inside the bottle can't go out.

  • If compressive shock is formed at upstream of bottle that will reduce stagnation pressure at downstream and make the fluid inside the bottle difficult to come outside.

  • Fluid may go out because of inertial effect, if velocity of moving bottle is reducing but this will happen only if inertial force is grater than pressure force.

  • It will go outside if its stagnation pressure is more than external stagnation pressure this is not possible unless we supply some energy to bottle to increase pressure inside the bottle.

Method to verify this process

  • Transient CFD simulation this is relatively easy one
  • Mathematical modelling this process in differential form and solving. This is tough one
  • Experimental process using flow visualization like schlieren or shadowgraph with PIV. It is very expensive.

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