# Shock-Absorber Rotary Generator for Automotive Vibration Energy Harvesting
## 4 Analysis of the Blade Characteristics with ANSYS Fluent  
### Pro-Processing Step  
The characteristics of the blades by fluid flow delivered from the road's surface were analyzed using ANSYS Fluent. The main aim of this analysis was to derive the A-A curve of the blade. Figure 8 shows the modeling of the flow analysis.  
The blades were modelled using commercial software CATIA. Using the Import function, the blades were produced in ANSYS Geometry, and the fluid around the blades was modeled using the Subtract function in Boolean.  
The oil SAE10W-SAE30W oil is used as the shock absorber [14]. The fluid used in this analysis was SAE 30 W. Figure 9 and Table 2 present the characteristics of the fluid according to the change in temperature.  
Figure 8: ANSYS Fluent modeling.  
Figure 7: Road roughness.  
For simplicity of analysis, the fluid temperature was chosen as the normal temperature. Table 3 lists the fluid properties at normal temperature.  
The Reynolds number was calculated to select a model for CFD. This checked whether it was laminar or turbulent, and the equation is expressed as follows:  
\[Re=\frac{\textit{inertia force}}{\textit{viscous force}}=\frac{\rho VD}{\mu}=\frac{ VD}{\
u}=\frac{881.5\times 0.2138\times 0.09}{0.2394}=70.8514 \tag{2}\]  
where \(V=\) average velocity of the flow; \(D=\) characteristic length; \(\mu=\) dynamic viscosity; \(\
u=\) kinematic Viscosity; \(\rho=\) density.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature (K)** & **Dynamic Viscosity (N*/m2)** & **Kinematic Viscosity (mm2*s-1)** & **Density (kg*m-3)** \\ \hline
273 & 1.1241 & 1257.25 & 894.1 \\
283 & 0.4911 & 553.2 & 887.8 \\
290 & 0.23939 & 271.56 & 881.5 \\
303 & 0.12842 & 146.7 & 875.4 \\
313 & 0.07455 & 85.76 & 869.3 \\
323 & 0.04643 & 53.8 & 863.0 \\
333 & 0.03058 & 35.69 & 856.9 \\
343 & 0.02117 & 24.89 & 850.6 \\
353 & 0.01528 & 18.1 & 844.4 \\
363 & 0.01142 & 13.62 & 838.3 \\
373 & 0.0088 & 10.58 & 832.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Characteristics of the fluid at normal temperature.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Temperature & 293 K \\ Dynamic Viscosity & 0.2394 N*/m2 \\ Kinematic Viscosity & 271.56 mm2*s-1 \\ Density & 881.5 kg*m-3 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Characteristics of the fluid in this study.  
Figure 9: Characteristic graph of the fluid.  
The Reynolds number was calculated to be 70.8514, indicating that the model in this analysis proceeded in laminar flow. The blade was rotated using the Reference Frame and Mesh Motion functions in ANSYS Fluent. Mesh Motion moves the mesh to follow the changing geometry of the boundary by moving the points at all stages of the analysis. Figure 10 shows the mesh used in the analysis.  
The input data were the inlet velocity of the fluid and the angular velocity of the blade. The velocity of the inlet calculated using CarSim-Simulink was 0.2138 m\(\cdot\)s\({}^{-1}\). The torque was measured by changing the angular velocity of the blade. Zero rad/s was used as the initial value, and the angular velocity was increased gradually so that the resulting torque was 0.