**4.2 Transient flow**

In this section the transient simulations results are presented. **Figure 7** represents the evolution of vapor volume fraction at different times for L2/d2 = 5. The inlet corner radius rc is equal to zero. The injection pressure *pin* = 1000 bar and the exit pressure *pout* = 50 bar.

The cavitation appears in the vicinity of the sharp edge for a time of the order of 0.6 μs. Then, the cavitation pocket elongates progressively through the orifice and reaches the nozzle exit at t = 3 μs. This result agrees well with the numerical

*Analysis of Geometric Parameters of the Nozzle Orifice on Cavitating Flow and Entropy… DOI: http://dx.doi.org/10.5772/intechopen.99404*

**Figure 6.** *Discharge coefficient as a function of rc/d2 ration for Re = 2 103 and Re = 6.8 103 .*

**Figure 7.** *Transient evolution of vapor volume fraction.*

simulation obtained by Dumont et al. [37] in a similar injector and by experimental visualization and measurements Ohrn et al. [33].

**Figure 8** depicts the axial profile of the mixture density near the wall at t = 1.5 μs and t = 3.8 μs. Upstream of the corner the fluid is at liquid state.

At the sharp edge, the density exhibits an important decrease due to the pressure drop and the appearance of cavitation. In this region, the mixture density contains mainly fuel vapor.

Downstream the corner, the mixture density increases and the vapor fraction decreases, owing to the collapse and the breakup of the cavitation along the orifice.

At the nozzle exit, the cavitation is present for t = 3.8 μs and therefore the mixture density is smaller than the liquid density *ρl*. Thus the spray that leaves the injector and penetrates into the combustion chamber is formed not only by fuel liquid but also by fuel vapor.

**Figure 8.** *Mixture density profile at t = 1.5 μs and t = 3.8 μs near the nozzle wall.*
