Generic Properties of Flows in Low-Speed Axial Fans Operating at Load-Controlled Windmill

Ortolan, Aurélie; Courty-Audren, Suk-Kee; Lagha, Massyl; Binder, Nicolas; Carbonneau, Xavier; Challas, Florent

doi:10.1115/1.4040678

Cited by 8 publications

(7 citation statements)

References 16 publications

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“…From all the references aforementioned, it is possible to draw a generic picture of the gradual transition of a compressor toward turbine operation, at least in incompressible flows. The formalism used in this paper is adapted from Binder et al (2015) and Ortolan et al (2018). The hatted quantities .…”

Section: Theoretical Expectations At Free-windmilling Regimementioning

confidence: 99%

“…Actually, the linear behaviour is preserved because no massive separation is triggered on the rotor blades at free-windmilling flow-coefficient, contrarily to the diffuser blades in which they were frequently reported at free-windmilling, and even at lower flow-coefficients . Comparable separations appear on the rotor farther along the operating characteristic, at higher flowcoefficient, in the load-controlled wind-milling regime for which the fan recovers work from the flow (Ortolan et al, 2018). However the different studies of the literature where conducted for Reynolds numbers high enough to promote an early transition of the boundary layer on the rotor blades.…”

Section: Introductionmentioning

confidence: 99%

“…Figure 1: Theoretical expectations in incompressible flows while increasing the flow coefficient φ. Adapted from Binder et al (2015) and Ortolan et al (2018).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Influence of the Reynolds number on the free-windmilling operation of a small dimensions fan.

Binder,

Sanchez,

Thacker

et al. 2023

European Conference on Turbomachinery Fluid Dynamics and Thermodynamics

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The literature dedicated to the wind-milling performance of fans reports that fair accuracy is at the reach of low-order modelling, at least for the prediction of the freewindmilling regime. However the different studies of the literature where conducted for Reynolds numbers high enough to promote an early transition of the boundary layer, and avoid massive separations on the pressure side of the rotor blades. The present paper describes an experimental analysis of the free-windmilling regime, on a low dimension fan designed for cooling applications in aircrafts. The WilLow test facility gives access to this regime for different mass-flows, i.e., different Reynolds numbers. For the highest Reynolds number configuration, it is demonstrated that the flow structure is in accordance with the theoretical expectations, and a linear evolution is observed in the loadingto-flow coefficient map. However, the low Reynolds-number configuration induces strong non-linearities, for which massive separation on the rotor blades is suspected. The flow structure is then completely recast, and the span-wise work distribution is affected. The linearity of the loading-to-flow coefficient is then lost, which results in a different value of φ p , which is no more predictable by the available low-order methods. Finally, the ability of more resolved numerical simulations to keep track of this delicate physics effect is checked. KEYWORDSWindmilling, Fan flows, Reynolds effect NOMENCLATURE H blade height h t total enthalpy k, κ n model constants M Mach number r, r h , r s , r p radius, radius at hub, radius at shroud, zero-work radius Re Reynolds number V , W & U absolute, relative & blade velocities α flow angle in the absolute frame of reference β flow angle in the relative frame of reference ψ loading coefficient φ flow coefficient φp free-windmilling flow coefficient

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Section: Theoretical Expectations At Free-windmilling Regimementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Influence of the Reynolds number on the free-windmilling operation of a small dimensions fan.

Binder,

Sanchez,

Thacker

et al. 2023

European Conference on Turbomachinery Fluid Dynamics and Thermodynamics

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“…Detailed information about the sensors used in this study can be found in Ortolan et al [7]. Although no global measurement is available with distortion, local measurements are available in Sections 2 and 3 ( Figure 2, right).…”

Section: Instrumentationmentioning

confidence: 99%

Body Force Modeling of the Aerodynamics of a Low-Speed Fan under Distorted Inflow †

Bénichou

Dufour

Bousquet

et al. 2019

IJTPP

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New propulsive concepts, such as boundary layer ingestion, involve stronger interactions between the engine and its environment, and are thus more complex flows compared to classical architectures. Usual turbomachinery design tools are inadequate, and new numerical methodologies are needed to accurately predict the engine performance with affordable CPU resources. The present paper examines the relevance of a reduced-order modeling approach—the body force modeling (BFM) method—for a low-speed cooling fan with inflow distortion. The formulation itself accounts for the blade metal blockage and compressibility effects, and it relies on a semiempirical loss model, independent of computational fluid dynamics (CFD) calibration. The BFM results obtained in the present work are assessed against full-annulus unsteady Reynolds-averaged Navier-Stokes (URANS) results and experiments. The comparison shows that the BFM approach successfully quantifies the fan stage performance. Furthermore, the distortion transfer across the stage is examined and the flow patterns observed are found to be the same as in the URANS results and in the measurements. Hence, this methodology, coming at a low CPU cost, is well-adapted to the early design phase of an innovative propulsion system.

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“…Research performed by Hirayama et al [7] indicated that rotor blades in the FW and HL windmilling states had different load dispersions across not only the spanwise direction but also the chordwise directions. Additionally, research on the rotor performance and internal flow was performed by Ortolan et al [8] The load characteristics of blades and the internal flow in the windmilling state are attracting increasing research attention. However, several areas still require further research, including the unsteady flow structure around the separation area, the loss mechanism, and the extractable workload from rotor blades.…”

Section: Introductionmentioning

confidence: 99%

Rotor Performance of an Axial Flow Compressor at Free and Highly Loaded Windmilling Conditions

Zhang

Fujisawa

Ohta

et al. 2020

JGPP

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The work characteristics and loss-generation mechanism of a single-stage axial flow compressor in windmilling operation were investigated via experiments and computational fluid dynamics analyses. The windmilling state occurs when air flowing through an unlit engine drives the compressor rotor blades, similar to a turbine. This phenomenon applies mostly to aircraft engines, where it is caused by ram pressure. When the inlet flow coefficient is gradually increased in the design, the rotor blades gradually enters the windmilling operation from the tip toward the hub. This research has focused on two windmilling operations: free windmilling (FW) and highly loaded (HL) windmilling. In the case of FW, the net work performed by the rotor blades to the fluid is canceled out (zero), and the rotor is in an idle state. In the HL windmilling condition, the work performed to the rotor blades by the fluid increases, the compressor acts as a turbine, and power is generated. According to the detailed numerical results, the total-pressure loss under the free and HL windmilling conditions was mainly caused by three flow structures: (1) tip leakage flow from the suction surface (SS) to the pressure surface (PS) near the leading edge and that from the PS to the SS near the trailing edge; (2) the interaction of leading-edge separation vortices due to the highly negative incidence and the rotor leading-edge vortex; and (3) the boundary-layer separation near the hub wall. Surface-pressure measurement on a rotating rotor blade revealed that the distribution of the rotor operating mode existed not only in the spanwise direction but also in the chordwise direction under the windmilling operations. The turbine mode region was observed near the leading edge, while the compressor mode region was observed near the trailing edge, even in the HL windmilling condition. Therefore, the driving force of the windmilling was dominated not by the area of the turbine mode on the rotor surface but by the strength of the operating mode, i.e., the static-pressure difference between the SS and PS on the rotor. Finally, the unsteady flow field within blade-to-blades passages was investigated via an unsteady detached eddy simulation, and the differences in the loss-generation mechanism between the FW and HL windmilling conditions were examined. : Free windmilling : Highly loaded

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Generic Properties of Flows in Low-Speed Axial Fans Operating at Load-Controlled Windmill

Cited by 8 publications

References 16 publications

Influence of the Reynolds number on the free-windmilling operation of a small dimensions fan.

Influence of the Reynolds number on the free-windmilling operation of a small dimensions fan.

Body Force Modeling of the Aerodynamics of a Low-Speed Fan under Distorted Inflow †

Rotor Performance of an Axial Flow Compressor at Free and Highly Loaded Windmilling Conditions

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