# Numerical Simulation of Cavitation Erosion Aggressiveness Induced by Unsteady Cloud Cavitation
## 3 Results
### Influence of Driving Pressure Definition
From a general overview, it can be confirmed that the value of \(p_{d}\) has a significant influence on the results. Figure 7: _Cont._  
The results presented in Figure 6a at instant 1.0 show that the highest condensation processes take place at both ends of the attached cavity. In Figure 7, it is also confirmed that the values of \(p(t)\) in the condensation regions at this instant are higher than the corresponding values of \(\overline{p}\). It can be seen that a higher \(P_{den}\) is predicted on the fluid using \(p(t)\), and correspondingly it results in a higher \(P_{load}\) on the hydrofoil surface. Likewise, at instant 1.1, the \(p(t)\) in the condensation region is also higher than \(\overline{p}\), leading to a locally higher \(P_{load}\). However, this is not a reliable result because, at this stage, when the sheet cavity is transformed into a cloud cavity, no strong collapses are expected to occur. The results presented in Figure 6c at instant 1.3 show condensation regions located on the margin of the cloud cavity because the pressure in its outer region is definitely higher than that within its interior as shown in Figure 7c. Moreover, \(p(t)\) is very low and even almost equal to the vapor pressure inside the cloud cavity region marked by the isoline, which implies that the pressure difference between the driving pressure and vapor pressure is close to zero. As a result, a very low aggressiveness on the hydrofoil surface is predicted. On the other hand, the use of \(\overline{p}\) determines a higher \(P_{den}\) and \(P_{load}\) at the condensation region. The final cloud collapse takes place at instant 1.44, as shown in Figures 6d and 7d, when a local value of \(p(t)\) over 1 MPa is predicted inducing the maximum values of \(P_{den}\) and \(P_{load}\). However, this instantaneous pressure peak is the consequence of the final collapse but it is not the pressure source driving the cavity collapse. Moreover, the appearance of this local pressure peak is considered by [PERSON] et al., [37] to be a spurious effect of the numerical calculation. In contrast, the \(P_{den}\) and \(P_{load}\) predicted using \(\overline{p}\) are much lower because the \(\overline{p}\) levels are significantly smaller than the \(p(t)\) ones. Finally, the area with the highest erosion power is mainly concentrated on the closure region of the sheet cavity as shown in Figure 7e at instant 1.6. In addition, a small cavity also appears after the final collapse of the cloud cavity due to the vortex rebound [38]. Comparing the results predicted using \(p(t)\) or \(\overline{p}\), the latter gives higher \(P_{den}\) and \(P_{load}\) because its level on the condensation area is higher than for the former. Similarly, the results at instant 1.8 allow us to verify the previous observations. Figure 7: Contours of \(p(t)\) (**top left**), \(\overline{p}\) (**top right**), \(P_{den}\) and amplitude of \(P_{load}\) along the chord (**bottom left and right**) obtained using \(p(t)\) (**left**) and \(\overline{p}\) (**right**). Red lines showing the value of the power load on the surface along the chord. Black isolines of \(\alpha_{v}=0.1\) show the locations of the main vapor cavities at each instant. Figure 8 shows the accumulated \(P_{tot\_load}\) levels along the hydrofoil chord during one shedding cycle from instant 1 to 2 using Equation (23) with \(P_{threshold}\) equal to zero. It is observed that \(P_{tot\_load}\) along the chord is much lower when using \(p(t)\) than \(\overline{p}\), with the exception of a small region near the leading edge when using the Zwart and the Sauer models. Another observation is that the \(P_{tot\_load}\) levels near the leading edge are even higher than those on the region where the cloud cavity collapses when using \(p(t)\).