Principle

Grid

Calculation conditions

Initialization of the domain

Analysis of the results obtained

Conclusion

The objective is to study an injector and to determine
the adequate conditions to obtain a high level of mixture at the exit of
the injector.

A flow of air enters by the left of the injector
with an horizontal velocity V_{o}=10m/s instead fuel is injected
by the two intakes with a vertical velocity V_{f}. So fuel is carried
out by the air flow and fuel and air are mixed to give an homogeneous mixture
at the exit of the injector. After the injector, there is the combustion
phase with the mixture coming from the injector.

*Scheme and dimensions of the injector*

To study the injector, we have used a unstructured grid like it is shown on the figure above. A structured grid may give results no more precise so the option of unstructure grid has been chosen.

*Grid used*

We have chosen to study the influence of the fuel velocity on the homogeneity of the mixture. We have considered three differents cases :

- Case 1 : V_{f}=50m/s

- Case 2 : V_{f}=10m/s

- Case 3 : V_{f}=25m/s

The air velocity is always the same : V_{o}=10m/s.

We had to solve Navier-Stokes equations of the flow inside the injector.

The calculation was dimensional and we have decided to use LES calculation. Effectively, the flow will be unsteady and turbulent inside the injector and turbulence is a positive point for the homogeneity of the mixture. Even if turbulence is 3D and our problem 2D, we can expect more precise results with LES calculation than laminar calculation. An other group of working has made laminar calculations so it will be interesting to compare results.

To start the calculation we had to proceeded to the initialization of the domain.

For this we have fixed velicities of air (V_{o}=10m/s)
and fuel (V_{f}=10, 25 or 50 m/s). We have also fixed mass fractions
of air (Y_{o}) and fuel (Y_{f}) on the different parts
of the domain :

- for the two intakes of fuel (0,05<y<0,09 and -0,09<y<-0,05)
: Y_{o}=0 Y_{f}=1

- for the rest of the domain : Y_{o}=1 Y_{f}=0

*Initialized domain*

__Analysis of the results obtained__

- Case 1 Results: V_{f}=50m/s

- Case 2 Results: V_{f}=10m/s

- Case 3 Results: V_{f}=25m/s

The study of the influence of the fuel velocity has shown that more the fuel velocity is high more the mixture is homogeneous. So for Vf=50m/s we have obtain more good results than for Vf=10 or 25 m/s where there is no efficient mixture.

We have seen also the limits of our calculation and the numerical errors produced during it : vortices which appear near of fuel intakes, the domain which is not long enough when structures begin to increase ....

Lastly, this work was a good opportunity to learn to use AVBP which is a calculating code well known in the domain of aerodynamics.