Fix latex in perp flap readme

Author: uekerman

perpendicular-flap/README.md

@@ -11,7 +11,7 @@ We model a two-dimensional fluid flowing through a channel. A solid, elastic fla
 
 ![Flap setup](images/tutorials-perpendicular-flap-setup-drawing.png)
 
-The simulated flow domain is 6 units long (x) and 4 units tall (y). The flap is located at the center of the bottom (x=0) and is 1 unit long (y) and 0.1 units thick (x). We set the fluid density $$ \{rho}_F= 1.0kg/m^{3} $$, the kinematic viscosity $$ \{nu}_f= 1.0m^{2}/s $$, the solid density $$ \{rho}_s= 3.0·10^{3}kg/m^{3} $$, the Young’s modulus to $$ E= 4.0·10^{6} kg/ms^{2} $$ and the Poisson ratio $$ \{nu}_s = 0.3 $$. On the left boundary a constant inflow profile in x-direction of 10m/s is prescribed. The right boundary is an outflow and the top and bottom of the channel as well as the surface of the flap are no-slip walls.
+The simulated flow domain is 6 units long (x) and 4 units tall (y). The flap is located at the center of the bottom (x=0) and is 1 unit long (y) and 0.1 units thick (x). We set the fluid density $$ \rho_F= 1.0kg/m^{3} $$, the kinematic viscosity $$ \nu_f= 1.0m^{2}/s $$, the solid density $$ \rho_s= 3.0·10^{3}kg/m^{3} $$, the Young’s modulus to $$ E= 4.0·10^{6} kg/ms^{2} $$ and the Poisson ratio $$ \nu_s = 0.3 $$. On the left boundary a constant inflow profile in x-direction of 10m/s is prescribed. The right boundary is an outflow and the top and bottom of the channel as well as the surface of the flap are no-slip walls.
 
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