Coherent vortex structure investigation behind the axial fan in pipe

Abstract

Experimental investigation of the coherent vortex structure in pipe on the axial fan pressure side, by use of the velocity optical measurement techniques, is reported in this paper. Generated vortex structure, its velocity and turbulent statistical values are revealed and discussed. Experiments were conducted by use of the one-component laser Doppler anemometry (LDA) and stereo particle image velocimetry (SPIV) systems. In paper [1] is presented investigation of the non-gradient turbulent transfer in swirl flows, based on 2C LDA measurements, while in paper [2] is presented research of the turbulent swirl flow in pipe behind three axial fans, of which one is ZP30. Here is presented investigation of the turbulent swirl flow in pipe on the ZP22 axial fan pressure side. Generated complex flow is three dimensional, nonhomogeneous and anisotropic. Experimental installationExperimental test rig has a pipe 27.74 D long, where D = 0.4 m is the average inner pipe diameter. It has a profiled bellmouth inlet and axial fan at the inlet. This is, after international standard ISO 5801, case B, with free inlet and ducted outlet. Axial fan has outer diameter 0.399 m and nine adjustable blades. Ratio of the hub and outer diameter is ν = 0.5. This construction generates Rankine swirl flow. Measurements have been performed in the measuring section (z = 3.35 D) on the fan pressure side. Fan rotation speed was n = 1500 rpm and outlet angle at the outer diameter was 22 • . Measurements were performed with one component LDA system, Flow Explorer Mini LDA, Dantec, with BSA F30 signal processor and laser power 35 mW. Velocity components were measured subsequently. Axial and radial velocities were measured from side, while circumferential one from above and under the pipe due to laser focal length, but they overlap in the central region. Discussion of the LDA measuring volume position and its dislocation, due to the curved walls, is calculated and discussed in [3]. In addition, measurements with SPIV system, were conducted by use of the dual head Nd:Yag laser (30 mJ/pulse, 532 nm, 15 Hz) and two 12-bit CCD (charge-coupled device) cameras, lens 50 mm/F1.8, with resolution 1660 x 1200 pixels, and 32 fps. Successful flow seeding for both experimental methods was achieved by Antari Z3000II thermal fog machine.