We derive necessary conditions that traveling wave solutions of the
Navier-Stokes equations must satisfy in the pipe, Couette, and channel flow
geometries. Some conditions are exact and must hold for any traveling wave
solution irrespective of the Reynolds number (Re). Other conditions are
asymptotic in the limit Re→∞. The exact conditions are likely to be
useful tools in the study of transitional structures. For the pipe flow
geometry, we give computations up to Re=100000 showing the connection of our
asymptotic conditions to critical layers that accompany vortex structures at
high Re