Unsteady Flow and Wake Transport in a Low-Speed Axial Fan With Inlet Guide Vanes

Abstract

The present study is focused on the analysis of the dynamic and periodic interaction between both fixed and rotating blade rows in a single stage, low-speed axial fan with inlet guide vanes. The main goal is placed on the characterization of the unsteady flow structures involved in an axial flow fan of high reaction degree, relating them to working point variations and axial gap modifications. For that purpose, an experimental open-loop facility has been developed to obtain a physical description of the flow across the turbomachine. Using hot-wire anemometry, measurements of axial and tangential velocities were carried out in two transversal sectors: one between the rows and the other downstream of the rotor, covering the whole span of the stage for a complete stator pitch. Ensemble- and time-averaging techniques were introduced to extract deterministic fluctuations from raw data, both of which are essential to understand flow mechanisms related to the blade passing frequency. An exhaustive analysis of the measured wakes has provided a comprehensive description of the underlying mechanisms in both wake-transport phenomena and stator-rotor interaction. In addition, unmixed stator wakes, observed at the rotor exit, have been treated in terms of dispersion and angular displacement to indicate the influence of the blades loading on the transport of the stator wake fluid. The final aim of the paper is to highlight a complete picture of the unsteady flow patterns inside industrial axial fans.

Non-deterministic kinetic energy within the rotor wakes and boundary layers of low-speed axial fans: frequency-based decomposition of unforced unsteadiness and turbulence

“…The Reynolds number based on the tip speed and rotor chord length is 1.410 6 , and the tip clearance is 2.3% of the blade height. At nominal conditions, the volumetric flow rate is 16.5 m 3 /s with a total pressure increment of 1150 Pa. More details can be found in [36][37], and the main geometrical parameters are summarized in a table in the figure 2-b. Test sections and data grid on the windows.…”

“…Figure 3 illustrates the degree of convergence achieved with this election. The convergence of the phase-averaged data is presented only for the axial velocity component, which is more restrictive than the tangential one (axial velocity presents higher gradients and fluctuations than the tangential component [36]). The results are presented for two representative points, one placed at midspan and the other in the hub boundary layer (see the dashed lines in the time-averaged contour plot), for both nominal and near stall conditions.…”

“…In these studies, complemented also with numerical simulations [33][34][35], a multi-point traversing system was employed to obtain detailed distributions of the velocity field in several windows covering the passage span for a complete stator pitch. The data set obtained from this facility has been used to investigate many different flow phenomena including wake dispersion and wake transport [35][36], mean flow, turbulent structures and integral length scales [36][37], deterministic stresses [38] and secondary flows and tip vortex in similar fans [39][40]. At present day, as an alternative to the costly experimental campaigns, computational modelling has become an extended, well-mature discipline, especially useful in the design process.…”

Influence of Prewhirl Angle and Axial Distance on Energy Performance and Pressure Fluctuation for a Centrifugal Pump with Inlet Guide Vanes

“…Mohseni et al [3] presented three different novel IGVs designs for centrifugal compressors and the results showed that the s-cambered profile was preferred for applications with positive prewhirl. Cui [4] and Oro et al [5] focused on the unsteady flow for centrifugal compressors with inlet guide vanes, and analyzed the unsteady flow structures, periodic interaction, and wake transport. Johnston and Fleeter [6] performed experiments on pressure and velocity fields of wake-induced by IGVs for three IGV-rotor axial distances.…”

Turbulent dispersion via fan-generated flows

“…Limited studies on axial fan-generated flows in the immediate vicinity of the fan have shown that the flow indeed has a non-zero swirl velocity, and that the turbulence is inhomogeneous and anisotropic. 28,29 However, these studies have only focused on the flow field upstream and in close proximity to the fan. To our knowledge, experiments have not been conducted to characterize the turbulent dispersion of passive scalar quantities further downstream from an axial fan.…”