# Review of Passive Flow Control Methods for Compressor Linear Cascades
## 3 Discussion
### Analysis of Passive Control Methods
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Flow Control Method** & \multicolumn{2}{c}{**Advantages**} & \multicolumn{2}{c}{**Disadvantages**} \\ \hline \multirow{4}{*}{Gurney Flaps} & - & Effective in improving flow stability and reducing vortex formation. & - & May have a negative impact on the overall aerodynamics of the system at high speeds. \\  & - & Can help prevent stall and reduce pressure losses. & - & Performance decreases if groove height exceeds optimal range. \\ \cline{1-1}  & - & En reduce flow loss by 14.42\% at & - & Groove placement requires careful optimization [131] \\ \hline \multirow{4}{*}{Fences and Grooves} & - & Control corner separation and reduce vortex formation. & - & Complex in design and optimization. \\  & - & Provide improvements in cascade & - & May not be effective for all operational conditions. \\  & - & Aerodynamic efficiency. & - & The effectiveness of full-span slots \\ \hline \multirow{4}{*}{Slot Configurations (Blade End Slots, Full-Span Slots)} & - & Improve corner separation across all aspect ratios. & - & The effectiveness of full-span slots decreases at higher incidence angles. \\  & - & Help reduce the number of blades for better thrust-weight ratio. & - & May have minimal impact at certain operational conditions [119] \\  & - & Can reduce total pressure loss by up to 39.4\% under certain conditions. & - & May require more complex blade manufacturing [129; 130] \\ \hline \multirow{4}{*}{Vortex Generators (VGs)} & - & Reduce secondary flow development and extend stall range. & - & May slightly increase pressure loss at certain configurations. \\  & - & Can improve cascade performance & - & Can be sensitive to positioning and operational conditions [88] \\  & - & Can reduce total pressure rise. & - & May require more complex blade manufacturing [129; 130] \\ \hline \multirow{4}{*}{Micro-Vortex Generators (MVGs)} & - & Effective in delaying stall onset and suppressing secondary flow. & - & May not perform as effectively at lower Reynolds numbers. \\  & - & Reduces total pressure loss by up to 9.36\%. & - & Potential for limited application in some compressor designs [91] \\  & - & Improves performance under high-load conditions & - & More complex to implement and optimize. \\ \hline \multirow{4}{*}{Leading-Edge Strake Blades (LESB)} & - & Achieves a significant reduction in total pressure loss (59.7\%) while maintaining static pressure rise. & - & May require intricate manufacturing techniques. \\  & - & Substantial aerodynamic improvements. & - & May require intricate manufacturing techniques. \\ \hline \multirow{4}{*}{Porous Walls} & - & Suppress corner separation and vortex development. & - & The design may be challenging for some compressor configurations. \\  & - & Improve overall cascade performance. & - & Higher complexity in manufacturing. \\ \hline \multirow{4}{*}{Slanting Riblets} & - & Reduces drag by up to 16.8\%. & - & Limited effectiveness at higher Reynolds numbers due to turbulent mixing. \\  & - & Enhances flow mixing and suppresses near-wall turbulence. & - & May cause slight drag increase at high Reynolds numbers [144]. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Advantages and disadvantages of passive control methods. By combining bio-inspired designs, advanced flow control structures and AI-driven simulations, these approaches play a crucial role in minimizing pressure losses, enhancing flow transitions and optimizing overall compressor performance. This synergy of natural design principles, cutting-edge computational tools and innovative engineering techniques leads to more efficient and high-performing turbomachinery. Figure 12 illustrates the impact of these passive control methods on aerodynamic performance. * Loss reduction: Riblets and grooves stand out for achieving the highest reductions in total pressure loss (up to 36.4%), primarily by suppressing separation and energizing boundary layers. These techniques are particularly effective in high Reynolds number flows or regions with adverse pressure gradients.