Calculate Pressure & Speed of Submerged Water Jet 100mm Away

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Discussion Overview

The discussion revolves around calculating the pressure and speed of a water jet impacting an object located 100 millimeters from the nozzle opening. The context includes considerations of fluid dynamics in a high-pressure environment, specifically at a depth of 100 meters below sea level in salt water, with a focus on the complexities introduced by turbulence and buoyancy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks a formula to calculate the pressure and speed of the water jet, given specific parameters such as pressure, flow rate, and nozzle diameter.
  • Another participant suggests that there is no simple formula for this scenario and recommends looking into publications that simulate similar setups.
  • A third participant describes the behavior of a turbulent jet, noting that it spreads out in a cone shape and that velocity varies with both distance from the nozzle and radial distance from the centerline.
  • It is mentioned that the interaction of the jet with an object is influenced by the object's geometry.
  • One participant highlights the added complexity of a fresh water jet discharging into salt water, categorizing it as a turbulent buoyant jet and reiterating the lack of a straightforward solution.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of calculating the jet's characteristics with a simple formula, indicating that the discussion remains unresolved regarding the best approach to take.

Contextual Notes

The discussion acknowledges limitations related to the complexity of turbulent flow and buoyancy effects, as well as the dependence on the specific geometry of the object being impacted. There are unresolved mathematical steps and assumptions regarding the flow dynamics.

JoachimSa
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I am trying to calculate at what pressure and speed water from a high pressure water jet will hit an object 100 millimeters away from the nozzle opening, but i can't figure it out.

The nozzle will be used at approximately 100 meter below sea level in salt water. Its a circular nozzle with a diameter = 2 millimeters. The water from the water jet is at 400 bar and with a flow of about 60 liters per minute.

Does anyone know what formula to use?
 
I don't think there is a simple formula where you could just plug in numbers. There are certainly publications about that setup, you could check what they did to simulate the system.
 
A turbulent jet of liquid discharged into a large volume of the same liquid spreads out in a cone shape . Tests and simulations have determined that assuming a half angle of 11.8 deg for the cone is adequate for most practical calculations . Problem is that the velocity of flow varies not only with distance from nozzle but also with radial distance from the flow centreline . Velocity is highest on the flow centreline and fades away to zero at larger radial distances .

What actually happens when jet impinges on an object depends on the geometry of the object .
 
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This becomes doubly difficult if your water jet is fresh water discharging into salt water, as it is now a turbulent buoyant jet. Generally speaking there is no simple solution to this problem (buoyant or not).
 

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