Experimental investigation on the outlet flow field structure and the influence of Reynolds number on the outlet flow field for a bladeless fan

The outlet flow field of an annular jet for a bladeless fan was investigated experimentally using CTA (Constant Temperature Anemometer) hot-wire system in detail, at five Reynolds numbers ranging from 28,200 to 40,100. From the experiment results, it can be concluded that: (1) the time-averaged velocity in both the horizontal and vertical radial directions, and the time-averaged velocity and turbulence intensity on the axis, all increase with increasing Reynolds number; (2) some variation situations of Sk (skewness) and Ku (kurtosis) of PDF (Probability Density Function) for dimensionless fluctuating velocity on the axis inversely dependent on Reynolds number, indicating that the decrease of Reynolds number intensifies the motion of large-scale coherent structures; (3) the annular jet within the outlet flow field starts to converge about at the cross-section of 1.5d (d represents the throat diameter of the Coanda surface) at each Reynolds number; the lower part of the flow field is combined upwards into the upper part; this combination has been finished about at cross-section of 3d; (4) the combined jet is similar to a classical single jet, the peak decay slope increasing with increasing Reynolds number; also, the intrinsic flow mechanism of this flow field structure has been revealed.