Heat and Mass Transfer

, Volume 52, Issue 3, pp 621–634 | Cite as

Effect of jet-to-mainstream momentum flux ratio on mixing process

  • Alka Gupta
  • Mohamed Saeed Ibrahim
  • R. S. AmanoEmail author


Temperature uniformity after a mixing process plays a very important role in many applications. Non-uniform temperature at the entrance of the turbine in gas turbine systems has an adverse effect on the life of the blades. These temperature non-uniformities cause thermal stresses in the blades leading to higher maintenance costs. This paper presents experimental and numerical results for mixing process in coaxial ducts. The effect of increased jet-to-mainstream momentum flux ratio on the temperature uniformity of the exit flow was analyzed. It was found that better mixing of primary (or hot) stream and dilution (or cold) stream was achieved at higher flux ratio. Almost 85 % of the equilibrium mixture fraction was achieved at flux ratio of 0.85 after which no significant improvement was achieved while the exergy destruction kept on increasing. A new parameter, ‘Cooling Rate Number’, was defined to identify the potential sites for presence of cold zones within the mixing section. Parametric study reveals that the cooling rate numbers were higher near the dilution holes which may result in rapid cooling of the gases.


Mixture Fraction Flux Ratio Exergy Destruction Momentum Flux Ratio Dilution Zone 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols


Area of cross-section of cladding


Area of cross-section of exit section


Total area of cross-section of the dilution holes


Area of cross-section of outer duct


Specific exergy destruction


Mixture fraction


Weighted average mixture fraction


Equilibrium mixture fraction


Specific enthalpy


Jet-to-mainstream momentum flux ratio

\( \dot{m} \)

Mass flow rate


Specific entropy




Adiabatic, ideal mixing temperature


Local temperature


Dilution jet temperature


Main (or primary) stream temperature, before mixing


Friction velocity at the nearest wall

ν, V


Vave exit

Average exit flow velocity

Vave prim

Average primary inlet flow velocity


Distance to the nearest wall



Kinematic fluid viscosity


Density of fluid


Wall shear stress



Dilution jet


Mixed stream at the exit



p, prim

Primary air

s, sec

Secondary air


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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Alka Gupta
    • 1
  • Mohamed Saeed Ibrahim
    • 1
  • R. S. Amano
    • 1
    Email author
  1. 1.Department of Mechanical EngineeringUniversity of Wisconsin-MilwaukeeMilwaukeeUSA

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