The problem I foresee is that whatever you do you cannot increase the pressure of the air in the throat without stalling the flow, you are relying on the 'ram' effect to force air into a smaller and smaller volume, and this it will not do. The pressure might rise a tiny amount in the throat, but only until the ram pressure equals the static pressure, then flow stops. To turn your turbine you convert the kinetic energy of the air stream to rotational (torque) at the turbine shaft. If you were driving the turbine, then this venturi setup works, cause you are adding energy to a volume of air, and sucking it through the duct, but to get torque from the airstream, you need force times distance, and as the force you get from the air mass is dependent on the airspeed, the only other way to get more force is to increase the distance the force works over, the blade length. So, long thin blades, like glider wings, will extract energy from the airstream very efficiently, a small 'fan' in a duct will be lucky to overcome the drag of its bearings.
Evan, WB #12