LES-based simulation of the time-resolved flow for rotor-stator interactions in axial fan stages

Oro, Jesús Manuel Fernández; Meana-Fernández, Andrés; Vega, María Isabel Álvarez; Pereiras, Bruno; González, José

doi:10.1108/hff-10-2017-0421

Cited by 8 publications

(3 citation statements)

References 32 publications

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“…The LES approach had been used to capture the unsteady flow-field at off-design operating conditions. According to the basic idea of LES, an average method must be adopted to distinguish large scale vortices that can be solved and small-scale vortices to be modeled [33]. Let variable u i be decomposed into u i and subgrid variables (modeled variables) u i .…”

Section: Governing Equations and Turbulence Modelmentioning

confidence: 99%

Unsteady Flow Characteristics of Rotating Stall and Surging in a Backward Centrifugal Fan at Low Flow-Rate Conditions

Zhou

Yang

et al. 2020

Processes

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The steady and unsteady flow characteristics of internal flow in a backward centrifugal fan of double inlet at low flow-rate condition are investigated by computational fluid dynamics in this paper. The investigation aims to reveal insights into generation mechanisms and our physical understanding of the rotating stall and surge. The numerical results mainly demonstrate that, with decreasing flow rate, a large number of vortex flows almost increasingly occupy the internal flow of the impeller. The reverse flow and separation vortices increasingly appear near the outlet of volute, and the internal flow of the impeller is completely blocked by the separated vortex flow at low flow-rate conditions. Results indicate that, due to a synchronization of the impeller rotation and separation vortex, these separated vortices act intensely on the pressure surface of the blade with time evolution, and the interaction between the separated vortices and surface of blade increasingly yields small-scale eddies. It is further found that the amplitude of pressure and velocity fluctuations gradually increase with the decrease of flow rate in a certain range. The unsteady characteristics acting on the volute tongue gradually increase in a range of Qd to 0.3 Qd (Qd is the design volume flow rate) with the decrease of flow rate, and the unsteady characteristics acting on the volute tongue are weakened at the working condition of 0.15 Qd. These insights clearly explain the unsteady nature of the rotating stall and surge phenomenon in the double inlet backward centrifugal fan.

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Section: Governing Equations and Turbulence Modelmentioning

confidence: 99%

Unsteady Flow Characteristics of Rotating Stall and Surging in a Backward Centrifugal Fan at Low Flow-Rate Conditions

Zhou

Yang

et al. 2020

Processes

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“…Special attention is devoted to the unsteady evolution of the tip leakage structures in the rotor passages in the relative frame of reference and how it is influenced by the operating flow rate of the fan. A full unsteady RANS simulation, taking advantage of a wellestablished sliding mesh technique used previously by the authors (Fernández Oro et al, 2019), has been adopted to describe accurately the blade passing frequencies of the fan. The numerical model has been validated with global variables for the performance curves and also with local measurements in the tip region to characterize the wall pressure fluctuations.…”

Section: Hff 3010mentioning

confidence: 99%

Stator–rotor interaction in the tip leakage flow of an inlet vaned low-speed axial fan

Gonzalez

Meana-Fernández

Fernández

2020

HFF

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Purpose The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan. Design/methodology/approach A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region. Findings It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes. Research limitations/implications Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy. Originality/value The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.

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“…In Kim et al (2012) conducted numerical simulations on MT1 turbine stage and stated the non-uniform turbine inlet temperature enhances the heat flux fluctuation on the blade tip and casing. Fernandez Oro et al (2019) adopted the large eddy simulation (LES) method to detailed investigated the rotor–stator interaction of aerodynamics performances.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigations of unsteady passing wake effects on turbine blade tip aerothermal performance with different tip clearances

Zhang

Qiang

et al. 2019

HFF

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Purpose The purpose of this paper is to numerically investigate the effect of guide vane unsteady passing wake on the rotor blade tip aerothermal performance with different tip clearances. Design/methodology/approach The geometry and flow conditions of the first stage of GE-E3 high-pressure turbine have been used to obtain the blade tip three-dimensional heat transfer characteristics. The first stage of GE-E3 high-pressure turbine has 46 guide vanes and 76 rotor blades, and the ratio of the vane to the blade is simplified to 38:76 to compromise the computational resources and accuracy. Namely, each computational domain comprises of one guide vane passage and two rotor blade passages. The investigations are conducted at three different tip gaps of 1.0, 1.5 and 2.0 per cent of the average blade span. Findings The results show that the overall discrepancy of the heat transfer coefficient between steady results and unsteady time-averaged results is quite small, but the dramatic growth of the instantaneous heat transfer coefficient along the pressure side is in excess of 20 per cent. The change of the aerothermal performance is mainly driven by turbulence-level fluctuations of the unsteady flow field within gap regions. In addition, the gap size expansion has a marginal impact on the variation ratio of tip unsteady aerothermal performances, even though it has a huge influence on the leakage flow state within the tip region. Originality/value This paper emphasizes the change ratio of unsteady instantaneous heat transfer characteristics and detailed the mechanism of blade tip unsteady heat transfer coefficient fluctuations, which provide some guidance for the future blade tip design and optimization.

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LES-based simulation of the time-resolved flow for rotor-stator interactions in axial fan stages

Cited by 8 publications

References 32 publications

Unsteady Flow Characteristics of Rotating Stall and Surging in a Backward Centrifugal Fan at Low Flow-Rate Conditions

Unsteady Flow Characteristics of Rotating Stall and Surging in a Backward Centrifugal Fan at Low Flow-Rate Conditions

Stator–rotor interaction in the tip leakage flow of an inlet vaned low-speed axial fan

Numerical investigations of unsteady passing wake effects on turbine blade tip aerothermal performance with different tip clearances

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