Air Flow Measurement Using an Airfoil

Perry, "The Chemical Engineer's Handbook", any edition.

With a little experimentation or estimation, you can determine the effect of angle of attack on lift. (Generally, for a symmetric airfoil, the CL is about .1 for each degree of attack angle from 1 through 10 or 12.) (However, how the airfoil is mounted, re proximity to walls, etc., will affect lift.) Then, with CL in hand you can measure lift force with a strain gauge (etc.) and apply the formula for lift, which is 1/2 rho x area x Vsquared x CL. (rho = mass density of the fluid.)

Perhaps even easier, is to simply measure lift, and measure flow with some other method in which you have some confidence. Then, knowing that lift varies with the square of speed, you can subsequently use the lift as the measure.