Abstract:
Summary.—The present report is one of a series dealing with N.P.L. methods for the design of return flow wind tunnels. Reports already issued deal with the design of the Compressed Air Tunnel¹ and Open Jet Tunnels,² with the design of corner cascades³ and fan straighteners, ⁴ and with the improvement of velocity distribution by means of windmills⁵ and gauzes.⁶
An explanation is now given of the method usually adopted in the design of fans for return flow tunnels ; as an example of the method, the design of the fan for the N.P.L. non-turbulent tunnel is considered in detail. It is shown that for a wind tunnel a fan with blades of constant chord is advisable ; and a formula is given by means of which a rapid estimate can be made of the variation in rotational speed of the fan corresponding to a variation in power factor at constant power.
