Quantitative studies of the wakes of freely flying birds in a low-turbulence wind tunnel

Exp Fluids (2003) 34:291–303

In Spedding et al. (2003), the drag calculated from the x-momentum equation in Eq. (10) is given in an incorrect intermediate form between two correct alternatives. The incorrect expression for the drag per unit span, D’, was written

$$ {D}\ifmmode{'}\else$'$\fi = \rho U^{2}_{0} {\int_{ - h/2}^{h/2} {{\left( {u(z) - u^{2} (z)} \right)}} }\,dz $$

(1)

for integrating through a wake profile, u(z) over height h. The correct versions are

$$ {D}\ifmmode{'}\else$'$\fi = \rho U^{2}_{0} {\int_{ - h/2}^{h/2} {{\left( {\frac{{u(z)}} {{U_{0} }} - {\left( {\frac{{u(z)}} {{U_{0} }}} \right)}^{2} } \right)}} }\,dz $$

(2)

or

$$ {D}\ifmmode{'}\else$'$\fi = \rho {\int_{ - h/2}^{h/2} {{\left( {U_{0} u(z) - u^{2} (z)} \right)}} }\,dz$$

(3)

The calculations in the paper are correct, and do not reflect the typographical error.