Interesting Applications of Turbulent Jets

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

Author: Dr. Sharad N. Pachpute (PhD.)

Overview of 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 have 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 bathrooms, utensils,s and vehicles, etc.

  Introduction to a Simple Jet

  •  A jet is defined as a wall-free shear flow with 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 the 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
   

Applications of Turbulent Jet

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.

  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 ratioα  = 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

 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 aircraft developed by Lockheed Martin.
  • Due to the vertical jet produced by the 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

 Rocket Jets for Thrust Generation

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

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
                                      

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
                                      

Scope of CFD for Turbulent Jets

Modeling Turbulence:

  • Turbulent flows are chaotic and complex, making them challenging to model accurately.
  • CFD uses various turbulence models like the Reynolds-Averaged Navier-Stokes (RANS) equations, Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS) to represent turbulence behavior in jet flows.
  • Each model has its strengths and limitations, impacting the scope of analysis and the level of detail achievable.

Jet Dynamics:

  • CFD can simulate the dynamics of turbulent jets, including their formation, development, and decay.
  • This encompasses studying phenomena such as jet spreading, entrainments of ambient fluid, mixing characteristics, and the evolution of turbulent structures within the jet.

Flow Visualization:

  • CFD enables the visualization of flow fields, velocity profiles, pressure distributions, and turbulence parameters within turbulent jets.
  • This helps in understanding flow patterns, identifying recirculation zones, locating areas of high turbulence intensity, and assessing mixing efficiency.

Heat and Mass Transfer:

  • Turbulent jets are integral to applications involving heat and mass transfer, such as in industrial processes, environmental studies, and combustion systems.
  • CFD can model convective heat transfer, species transport, and chemical reactions within turbulent jets, aiding in optimizing designs and improving performance.

Jet Noise Prediction

  •  CFD combined with acoustic modeling techniques can predict the noise generated by turbulent jets, which is crucial for aircraft and automotive industries, as well as environmental impact assessments near airports or industrial facilities.

Validation and Optimization:

  • CFD allows for the validation of experimental data through numerical simulations, facilitating the assessment of model accuracy and providing insights into discrepancies.
  • Additionally, CFD-based optimization techniques can be applied to improve jet designs, enhance performance, and reduce undesirable effects such as noise or pollutant emissions.
  • Multi-phase Flows: Turbulent jets often involve multi-phase flows, such as liquid-gas or solid-gas mixtures. CFD can handle such complexities, modeling interactions between phases, phase change phenomena, particle dispersion, and droplet/bubble dynamics within turbulent jet environments.

Applications:

  • The scope of CFD for turbulent jets extends across various fields,
    • Aerospace (jet engine design,
    • Basic of Airfoil and Aerodynamics,
    • automotive (fuel injection, exhaust systems),
    • environmental engineering (pollutant dispersion, ventilation),
    • process industries (mixing, drying, cooling),
    • research (fundamental turbulence studies, academic research).

Summary

  • Overall, CFD for turbulent jets offers a comprehensive framework for studying and analyzing intricate fluid dynamics, providing valuable insights for engineering design, optimization, and scientific investigations across a wide range of applications.

1 thought on “Interesting Applications of Turbulent Jets”

Leave a Comment