acceleration following a fluid particle


Senior Member
"acceleration following a fluid particle down the center of a nozzle is to be estimated."

Above sentence is from a fluid mechanics book and context is about fluid kinematics that is accelerations, velocities etc.

Sentence confuses me because, I think accelerations do not follow fluids or fluids particles but fluids or fluid particles do have accelerations. Can somebody explain it please?


Source: Fluid Mechanics by Çengel/Cimbala

Link to the source: 4.pdf
  • SReynolds

    Senior Member
    No. I'm fairly certain that the author talks about the change in the velocity/acceleration fields created as the fluid parcel moves along its path.

    This is coming from a person who has a fairly solid knowledge of vector calculus but no formal history of learning fluid mechanics. You should probably ask this question on a physics forum as well to be sure.


    Senior Member
    English - South-East England
    'Following' doesn't mean "coming after" here, it means "tracking, keeping up with". The distinction is between properties such as acceleration of a specific particle (or group of particles) as it moves, and those properties at specific locations as different particles move through the location. The first kind follows (tracks) the particles.


    Senior Member
    Exactly. In this specific case, it is not the particle that has the acceleration, it's the velocity field of the fluid that's changing. The acceleration is said to follow the particle because the change traces the movement of the parcel. In particular, as the fluid parcel follows its trajectory, the disturbances caused by this movement alter the fluid flow and create a change in the velocity field, which is realized as acceleration.
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