Particles Trajectories Through an Axial Fan and Performance Degradation due to Sand Ingestion

Abstract

The erosion of an axial fan was investigated, both theoretically and experimentally. A computer program was developed to predict particle trajectories and erosion through turbomachines. It also accounts for different boundary conditions and stage interfaces. The governing equations of the particle motion were solved using Runge-Kutta Fehlberg technique in a given flowfield. The tracking of particles and their locations are based on the finite element interpolation method. The methodology was applied to an axial fan with inlet guide vanes (IGV). The flowfield was solved using the TASCflow code. The number of particles seeded upstream of the IGV was determined from experimentally measured profile concentration, with respect to a random distribution of particle sizes. The erosion of the blades and changes to the chord and tip clearances were also measured. The concentration profiles and velocities of the particle were measured with a laser transit anemometer and used as input to the trajectory code. The fan performance was measured before and after sand ingestion to assess the degradation in performance due to the eroded geometry

Effects of Sand Ingestion Through an Axial Fan With Blade Staggering

“…According to this study and the reported in references [5,10], the erosion phenomenon is shown to reduce the blade chord progressively from the mid-span to the tip region, distort (blunt) the blade surface at leading edge and increase the tip clearance. The aerodynamic performance degradation for this axial fan can be assessed by a similar approach to that given by Ghenaiet et al [10] based on an erosion fault models.…”

“…The simulation of particle motion in turbulent flows requires the determination of the instantaneous flow velocity components corresponding to a particular eddy, which are calculated from the local turbulence properties of the flow, by considering a Gaussian random number [5,20]. The turbulence effect on a particle (mainly for small size) is assumed to prevail as long as the particle-eddy interaction time is less than the eddy lifetime, and its displacement relative to an eddy is less than the eddy length, which are estimated according to Gosman and Ioannides [21].…”

“…When the same compressor was subjected to an ingestion of 25 kg of sand over 605 seconds, a noticeable deterioration of 3.5 % in stage loading coefficient and 4 % in efficiency were measured [4]. Ghenaiet et al [5] reported a 7.1 % loss in adiabatic efficiency, a 9.5 % loss in pressure rise coefficient and a 55 % drop in surge margin in a high speed (11500 rpm) contra-whirl axial fan, after 9 hours of sand (MIL-E5007E) ingestion. The anticipated drop in the performance is due to increase in the angle of attack, which tends to shift the stall point to higher mass flow-rates.…”

“…The local change in roughness accounts for some of the performance degradation, but most losses are due to the blunt leading edge and changes to the tip region of the blade. Indeed, high erosion wear was found near the leading edge and over the upper corner of the pressure side, extending to the tip, hence, resulting in a tip clearance increase by 65.7 % and a tip chord reduction by 10.4 % [5]. Also, Suder et al [6] and Roberts [7] indicated that the penalty for blade leading-edge roughness and erosion can be significant, and as the rotor leading edge becomes rough, blunt and distorted from the nominal shape, the aerodynamic performance of high speed compressors suffers.…”

“…Particle trajectories computation is based on a stochastic tracking algorithm, which includes eddy-lifetime concept for turbulence, and accounts for the complex flow patterns near walls, random particle rebound factors, in addition to particle size distribution, non-spherical shapes and fragmentation, hence resulting in the improvement of the present trajectory code. Its validation was based on comparisons between predicted and measured mass erosion, geometry deterioration and aerodynamic performance degradation, Ghenaiet et al [5,10]. Further, it was used in many other studies as reported by Ghenaiet [11][12][13].…”