Interesting Applications of Turbulent Jets

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What are major applications of turbulent Jets in industries and nature?

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  Dr. Sharad N. Pachpute (PhD.)

1. Overview for Applications of  Jets

  •  A turbulent jet is any fluid flow with high velocity coming out from the nozzles or pipes. It is used for a lot of domestic,  industrial and natural applications
  • Jets has some applications
    • Thrust Generator in Ramjet, Turbofan, Rocket launching etc.
    • Natural Jets under gravity like water wall, water flow from the pipe
    • Turbulent Buoyant Jet (Forced Plumes) in Erupted Volcano and Weapon test
    • Turbulent Igniter Jet in the combustor of Jet /IC engine
    • Turbulent Forced Jet for Heating and cooling
    • Water jets for cleaning bathroom, utensil and vehicles etc.

  2.  Introduction to a Simple Jet

  •  A jet is defined as Wall free shear flowwith an initial source of momentum
  • Higher momentum means higher velocity or higher mass flow rate for a given geometry
  • Newtons second law of motion can be used to find the various forces (inertia, pressure, viscous and gravity) acting on the fluids
  • With an increase in the flow rate, the jet changes from laminar to turbulent  flow
  • Most of  jets are turbulent flow in nature. Hence, understanding of turbulent flow is essential to know the flow physics and its statics
  • Turbulent flows are chaotic with fluctuating velocity, pressure and other quantities. Such flows are studied statically to find average quantities. Averaged parameters are used to design the engineering systems
  • For complex problems of hot or cold jets, combustible flows, energy and chemical kinetics play significant roles for jet flows
  • Example: Water Jet from a Tap
   

2. Applications of Turbulent Jet

2.1 Thrust Generator: 

  • Turbulent jets are used to generate thrust for propulsion of rocket and missiles
  • In Jet Propulsion systems :  Ramjet, turbojet, turbofans, rocket engines etc.
  • Example: Ramjet (missiles)
  •       Ram jet missiles takes the air from surrounding atmosphere. The air mixes with the fuel kept in the combustion chamber. The  pressure and temperature generated flue gases are exhausted from the nozzles which generate high velocity jets
  •        The high velocity hot jets generate the thrust to push the missile as per second and third of motions
  •        Principle of ramjet missile is shown below
  • Another examples is Akash missile developed by DRDO of India.

2)  Jet Engine 

  • The principle of thrust generation is similar to ramjet engines. Only the difference is that fans and multi-stage axial compressors are added in a jet engine to provide high pressure air. Gas turbines are added to generate power for initial power and heating, cooling in aircraft
  • In turbofan jet engines, the jets are generated by fans and nozzles. The total air inducted by the fan is divides as , Total inlet air = Fan mass flow rate of air  + Core mass flow rate of air
  • Turbo-jet  engines =  Turbo-jet +  Fan-jet
  • More than 90% of air is used to generate the cold jets
  • Air bleeding ratio: α  = Fan Mass flow rate of air / Core Mass flow rate of air
  •  Total Thrust  = thrust created by the turbo jet + thrust created by the fan jet
  • The formula for total thrust generated by hot and cold jet is given as below
  • Components of a Jet Engine for commercial air lines

3) Thrust Vectoring Nozzles for Modern Fighter Jets

2D Thrust Vectoring Nozzle:

  •   2D Thrust Vectoring Nozzle  is used for Short Take off Vertical Landing (STOVL) using a 2D Thrust Vectoring Nozzle
  • It is used by F-35 military air craft developed by Lockheed Martin.
  • Due to vertical jet produced by 2D thrust vectoring nozzle, its take of distance is very small. It can take off on a smaller warships

Fig 6. STOVL of F35
  • By changing the direction of 2D nozzle, the  landing of F-35 can be done on a smaller aircraft carrier
F-35 tests fell short, Pentagon report says - CNNPolitics

3D Thrust Vectoring Nozzle:

  • 3D Thrust Vectoring Nozzle used in Sukoi -30  fighter jets which  make an aircraft more maneuverable
  • Thrust-Vectoring flight control (TVFC) is obtained through deflection of the aircraft jets in some or all of the pitch, yaw and roll direction
  • To manipulate the direction of the thrust from its engine(s) or motor(s) in order to  control the attitude  or angular velocity of the vehicle
  • Examples: 3D Thrust vectoring nozzle on a Sukhoi Su-35S
  • The 3D thrust vectoring nozzles rotate in 360 degree with the axis of jet engines using the spherical movement of nozzle base

4) Rocket Jets for Thrust Generation

  •     Multi-jet Rocket for heavy payload: Multiple nozzles are used by rocket engines to lift heavy payloads
                                               

5) Turbulent Buoyant  jets and plumes 

  • Hot flue gases exhausted from chimney flows upward due to buoyancy . However, the gravity affect the momentum of flue gas jets
  •    Natural buoyant jet and plumes
    •  Jets from chimneys of thermal power plant
    •  Water jets from a water reservoir
                                      

6) Jets for heating and cooling applications  

  • High velocity jets of water and air is used for faster heating and cooling application in manufacturing and process industries
  • Turbulent jets have higher heat removal rate by convective heat transfer in the impingement regions
  • Heat treatment is carried with turbulent jet cooling
  •  Applications of water jets for cooling of iron rods
  • Cooling of heated cement kiln is carried out by air jets to maintain structural strength of kiln
    • Air jet cooling of a cement kiln
                           
    • Water jet cooling of a cement kiln and temperature field
                                      

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