In this project, i shall be using a filament of an incandescent bulb as my sensing part in the circuit that I shall build. When the air flow shall be zero, the filament resistance will be low and when the air flow is available, the filament resistance will of course drop simply because the air flow will remove the excessive heat that will be generated from the filament. The variation in the resistance will lead to a variation  in the voltage across the filament. The said variation will be picked up by the op-amp and the brightness of LED at the output will be varied proportional to the flow of the air.
- Make filament L1 by removing the glass of a brand new incandescent lamp.
-Power the circuit Using the 12V DC battery or power supply
You can design a regulated power supply with LM317, as it provides variable output depending on the value of variable resistor attached at its output pin.