## 6 Results and Discussion
### Pressure Variation on the Wall of the Converging Mixing Section
Figures 21 and 22 are presented to show how the pressure varies along the converging mixing section wall for ejector G2 and G2.1, respectively. ejector G2.2 results are similar; hence, they are not presented here. Like what has been observed in ejector G1, the pressure starts to vary when the primary flow jet gets closer to the wall. The pressure initially increases to reach a peak and then decreases as the flow is about to enter the throat. This is because the secondary flow impinges the converging wall as can be seen in Figure 23, hence the peak in the pressure variation curve. Around this region, the pressure is at maximum. The impinging flow is then divided into two streams; one enters the ET and the other stream diverts to the converging wall and forms circulation. Such flow circulation has been observed by [PERSON] et al. (2015) in their CFD simulations. Figure 20: The effect of the converging wall pressure change on the change of the secondary mass flow rate obtained from the one-dimensional model. Figure 21: Pressure variation along the wall of the converging mixing section (\(72.9\leq x\leq 99.259\) mm) of ejector G2.1 (top) and the geometrical contour of the converging mixing section wall (bottom). The operating conditions of sim 00\({}^{\prime}\) to 09\({}^{\prime}\) can be seen in Table 5 (correspond to sim no. 0\({}^{\prime}\) to 9\({}^{\prime}\)). Figure 22: Pressure variation along the wall of the converging mixing section (\(72.9\leq x\leq 99.259\) mm) of ejector G2.1 (top) and the geometrical contour of the converging mixing section wall (bottom). The operating conditions of sim 00\({}^{\prime}\) to 09\({}^{\prime}\) can be seen in Table 5 (correspond to sim no. 0\({}^{\prime}\) to 9\({}^{\prime}\)). Paying attention again to Figures 21 and 22, one can see that the curve peak (\"mountain\" curve size) decreases gradually as the \(P_{0}\) decreases. It is also observed that the curve pattern for simulation no. 4' (sim 04') is rather different, i.e., the decrease in wall pressure after the peak is not as steep as the others. The explanation for these two phenomena (the gradual decrease of the \"mountain\" curve size and \"anomaly\" of sim 04' curve) is as follows in conjunction with Figure 24. At higher \(P_{0}\), the secondary flow has higher momentum as it enters the ejector. This is because the shear effect between the two flows (primary and secondary) gets stronger. However, due to the larger diameter of the shock cell, the secondary flow will not be able to directly enter the ejector throat. Rather, it will impinge the converging mixing section wall before the flow divided into two streams (Figure 23) as explained before. Thus, the dynamic pressure (kinetic energy) will be converted to pressure as the flow hits the wall. The higher the momentum of the secondary flow is, the higher the pressure at the converging wall will be, and vice versa. This explains the gradual decrease in the \"mountain\" size in the two figures as the \(P_{0}\) decreases. Table 5.0 Streamlines plot (colored by pressure) started from the secondary flow inlet for ejector G2 with operating condition of simulation no. 0’ (Table 5), i.e., \(P_{0}=618\) kPa. Regarding the \"anomaly\" of simulation no. 4' (sim 04'), it is related to the shock cells position and size inside the ejector, particularly in this case, inside the converging mixing section. Looking at sim 04' in Figure 24, one can see that the end of one of the shock cells is located just before the ET inlet. Thus, the hypothetical annular duct formed is diverging. This will hinder the flow to accelerate. The decrease in the flow acceleration shows up in the pressure curve of sim 04' as a less steep pressure drop after the peak. Observing the Mach contour plot of the other simulations in this figure, it is clearly seen that the hypothetical annular duct near the ET inlet is converging and, therefore, the pressure drop in the curve is steeper because the flow has higher acceleration.