Detecting wind speed
It would help us if you described the turbine, and what sort of measurement and output you require in more detail. Hopefully an answer to your question will help you understand the details which may be missing.

For example, does it rotate faster proportionate with higher wind speed? Is it generating power, or just a voltage you intend to use for speed measurement? At what frequency do you need to measure wind speed? 

If your requirements can be met, just time each rotation of the "turbine".

There are several approaches:


Attach a small magnet to the "turbine" and use a Hall-switch to
detect the magnet. Due to their wide-spread use in the automotive
industry, Hall-switches are relatively low-cost, robust and easy to
obtain. This has no moving parts, and is immune to light and dirt.
A Hall-switch produces a digital output, and so is easier to use than
an analogue Hall-sensor 
Detect "turbine" rotation with an optical sensor, either using pat of
the "turbine", or attaching something to the turbine to interrupt or
reflect light. This is less robust than Hall-switch as it is
sensitive to light and dirt.


Use a simple microcontroller to convert the measurements into an appropriate output.

If you require much more information during a single revolution of the "turbine" add more detail to your question.

If you require a specific type of output, add more detail to your question.