Hi Vishal,
You can use the plot3 function to add cut line to your plot. The following Is an example, replace the second figure with the following code to see the cutlines.
%% Use you code upto end of figure 1 then add the following instead of your code
figure(2);
colormap(jet)
ax = gca;
surf(ax,XX,YY,VTHETA)
shading interp
pbaspect([(max(max(r))-min(min(r))) L_const 1])
colorbar('location','EastOutside');
title('Circumferential Velocity (v_\theta) (m/sec)');
caxis([0 0.4]);
view(0,90)
% Adding the Cut Lines
hold(ax,'on')
plot3(ax,[0.004,0.006],[0.00187,0.00150],[1,1],'k','LineWidth',3);
plot3(ax,[0.008,0.011],[0.01387,0.01350],[1,1],'k','LineWidth',3);
hold(ax,'off')
% End of Cut lines
