# Bio-Inspired Aerodynamic Noise Control: A Bibliographic Review
## 3 Leading Edge Serrations
### Aerodynamic Properties of Leading Edge Serrations  
Several studies (see Table 4) have consistently shown that leading edge serrations provided more gradual stall and superior post-stall performance, i.e., to maintain higher lift without adding drag in the post-stall region and at the same time to delay the stall occurrence by increasing the lift at high angles of attack. Therefore, it is believed that leading edge serrations could be practically used to enhance the aerodynamic properties of the aircraft at takeoff or approach conditions, as well as to suppress stall on rotor and propeller blades.  
Figure 6: Two forms of the modified NACA 0021 airfoils, reprinted from [72] with permission from AIP Publishing: (**a**) the chord changed sinusoidally in the spanwise direction; and (**b**) the geometric angle of attack varied sinusoidally along the span.  
\begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline
**Year** & **Authors(s)** & **Type** & **Inflow** & **Bionic Object(s)** & \(R_{e}\)**(10\({}^{5}\))** & **AoA C\({}^{\circ}\)** & **H/\(\epsilon_{0}\) (\%)** & \(\lambda/\epsilon_{0}\) (\%) & \(\lambda/H\) \\ \hline
1971 & Hersh and Hayden [44] & Sawtooth & Smooth & NACA 0012 airfoil & 2 to 3.33 & 0 to 16 & 0.27, 0.54, 0.84, 1.11 & 0.55, 10.6, 1.66, 2.22 & 2 \\ \hline
1972 & Amdrl and Nagel [45] & Sawtooth & Smooth & Two-bladed rotor & & 3.13, 6.25 & 12.5, 18.75 & 3.4 \\ \hline
1979 & [PERSON] [74] & Sawtooth & Smooth & NACA 0015 airfoil & 2 to 6 & \(-\)1 to 21 & 1.52 & 3.05 & 2 \\  & & & NACA 2412 airfoil & 2 to 6 & \(-\)1 to 24 & 1.03 & 2.06 & 2 \\ \hline \multicolumn{10}{c}{3D scale model of} \\  & & & & & an idealized & & & & \\
2004 & [PERSON] et al. [60] & Sinusoidal & Smooth & humpback whale & 5.05 to 5.2 & \(-\)2 to 20 & & \\  & & & & flipper & & & & \\ \hline \multicolumn{10}{c}{} \\  & & & & NACA 63(4)-021 & & & & & & \\
2007 & [PERSON] et al. [75] & Sinusoidal & Smooth & airfoil & 1.83 & \(-\)6 to 30 & 2.5, 5, 12 & 25, 50 & 2.08, 4.17, 5, 10, 20 \\ \hline
2007 & [PERSON] et al. [76] & Sinusoidal & Smooth & NACA 0020 airfoil & 2.74 to 2.77 & 0 to 22 & 4 & 41.74 & 10.44 \\ \hline
2009 & [PERSON] et al. [77] & Sawtooth & Smooth & NASA 63-414 airfoil & 0.2 to 2.01 & \(-\)10 to 45 & 0.61, 0.64 & 0.59, 0.84, 1.04 & 0.97, 1.30, 1.61 \\ \hline
2010 & [PERSON] et al. [47] & Sinusoidal & Smooth & NACA 0021 airfoil & 1.2 & \(-\)5 to 25 & 2.86, 57.11, 11.43 & 10.71, 21.43, 42.86, 85.71 & 1.88, 3.75, 7.5, 15 \\ \hline
2011 & [PERSON] et al. [78] & Sinusoidal & Smooth & NASA 0020 airfoil & 20 & 0 to 40 & 2.5 & 20 & 8 \\ \hline
2012 & [PERSON] et al. [79] & Sawtooth & Smooth & Flat plate & 1.4 to 2.1 & 0 to 25 & & & 1.15 \\ \hline
2012 & [PERSON] et al. [80] & Sinusoidal & Smooth & NACA 2412 airfoil & 5.7 & 0 to 20 & 2.5, 5 & 25, 50 & 5, 10, 20 \\ \hline \multicolumn{10}{c}{} \\  & & & NACA 63(4)-021 & & & & & & \\
2013 & [PERSON] et al. [81] & Sinusoidal & Smooth & airfoil & 0.5 & 0 to 90 & 24 & 25 & 1.04 \\ \hline
2015 & [PERSON] et al. [82] & Sinusoidal & Smooth & NACA 0021 airfoil & 1.2 & 20 & 1.5 & 11 & 7.33 \\ \hline \multicolumn{10}{c}{} \\  & & & & NACA 65(12)10 & & & & & & \\
2015 & [PERSON] et al. [52] & Sinusoidal & Smooth & airfoil & 1.5 & \(-\)10 to 30 & 5, 20, 30 & 5, 10, 20, 30 & 0.17, 0.25, 1.2, 4, 6 \\ \hline \multicolumn{10}{c}{} \\  & & & & NACA 0012 and & & & & & \\
2015 & [PERSON] et al. [83] & Sinusoidal & Smooth & 65(12)10 airfoils & 3,5 & \(-\)5 to 20 & 5, 10 & 6, 15 & 0.6, 1.2, 15, 3 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Selected investigations of aerodynamic effect of leading edge serrations (”\(\cdots\)” denotes “not clear”).