CHAPTER 3: PHYSICAL EFFECT OF VITIATION ON SCRAMJET ...

PHYSICAL EFFECT OF VITIATION ON SCRAMJET DESIGN
3.3.3 REACTIVE CASE (ER=0.51)
Now, we study the case of hydrogen injection with ER=0.51. The goal is to compute a combustion
efficiency which yields the same pressure results as in the experiment.
Several cases have been computed, depending on the way to compute the drag, the composition of the incoming
air (31%, 22% (reference) or 0% of water mass fraction in the incoming air).
Case 3b: ER=0.51 – vitiated airflow – Spalding’s drag coefficient. We do not tune automatically the combustion
efficiency ETAC(x) but assume a linear law. This approach predicts a computed maximum pressure which is too
low in comparison with the experimental pressure (there are more shocks).
Case 4: ER=0.51 – vitiated airflow – Corrected Spalding’s drag coefficient. Here the results are far better, since
we have a good agreement between computed and experimental data.
Case 4b: ER=0.51 –vitiated airflow (composition YH2O=0.31). Corrected Spalding’s drag coefficient.
4,00
3,00
2,00
1,00
0,00
Mach
0,00 0,50 1,00 1,50 2,00 2,50
2,00E+05
1,50E+05
1,00E+05
5,00E+04
0,00E+00
Figure 8 : Computed Mach number for several assumptions (ER=0.51)
Pressures
0,00 0,50 1,00 1,50 2,00 2,50
Figure 9: Pressure (Pa) for different assumptions (ER=0.51)
Cas3b
Cas4b
cas4
Cas3b
Cas4b
cas4
Exp
We clearly see here the differences between each case. The case 3b has a good x profile but its
maximum pressure is too low: the Spalding’s law alone cannot simulate the big shock effects occurring at the
injection point (the flow strongly interacts with the fuel jet generating a shock wave). To integrate this
3 - 6 RTO-TR-AVT-007-V2