# modelling a mix section of a RQL second stage burner

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December 4, 2023, 08:58
modelling a mix section of a RQL second stage burner
#1
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Gil Vaz
Join Date: Oct 2023
Posts: 6
Rep Power: 2
Hi,

I'm modelling a mix section of a second stage burner for my master's dissertation. I've already extracted the fluid volume from the CAD model.

As the burner is cilindrical and has 12 fuel inlets and 12 air inlets, I'm going to simulate only a slice of the fluid volume in order to reduce the computational cost (the slice has 30 degrees). The dimensions of the fluid volume are represented in the attachment image 20231203_234757.jpg (d_fuel=1 mm, d_air=8mm, radius of the first stage inlet products=45 mm, radius of the outlet = 72mm).

The products from the first stage flow through the section and mix with the fuel and air that are injected, leading to combustion (it's a reburning technique). However, for now I'm only interested in modelling the non reacting flow.

I've calculated the Reynolds number of the first stage products inlet (left inlet in the drawing) and I got Reynolds = 305. I've also calculated the Reynolds number of the outlet (right outlet in the drawing) and I got Reynolds = 617.For internal flows, Ithink that the transition to turbulent regime begins at Reynolds = 2300 (value in Incropera book). For the Reynolds calculation I'm using the inlet and outlet diameters, respectively.

So my question is: should I use a laminar model because the Reynolds is always under 2300 or should I use a turbulent model because the fuel and air injection will create eddies (vortices)?

Note: for the CFD results I've used the laminar model, the fluid is air and the residuals order was 10^-11.
The inlet velocities are 0.814 m/s for the products inlet, 5.134 m/s for fuel inlet and 2.419 m/s for air inlet.
Attached Images
 image burner 2.PNG (115.0 KB, 1 views) velocity burner 4.PNG (41.8 KB, 1 views) 20231203_234757.jpg (29.7 KB, 2 views) inagem burner.jpg (38.6 KB, 0 views)

 Tags internal flow, laminar, turbulent