POD analysis of the turbulent flow downstream a mild and sharp bend

Vester, Athanasia Kalpakli; Alfredsson, P. Henrik

doi:10.1007/s00348-015-1926-6

Cited by 39 publications

(18 citation statements)

References 36 publications

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“…Decomposition demonstrated that most of the fluctuations correspond to a swirl switching mode which is attributed to the bulk swirl topology [4]. The swirl switching mode is consistent with the Dean vortex oscillation which is observed in single-bended pipe flows [13] [14]. Additional flow field unsteadiness comes from a vertical oscillation of the shear layer which is associated with the diffusive flow separation at the first bend of the S-duct [5].…”

Section: Iintroductionsupporting

confidence: 60%

“…This is coupled with a lateral oscillation in the position of low axial-momentum region. This mode is associated with the Dean vortex motion which is widely reported downstream of bends in pipe flow [13] [14]. The other key mode, termed the vertical mode [4], corresponds to a vertical oscillation in the position of the region of low axial momentum and is associated with the unsteady shear layer which originates from the flow separation upstream in the duct.…”

Section: Modal Decompositionmentioning

confidence: 88%

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Influence of Upstream Total Pressure Profiles on S-Duct Intake Flow Distortion

McLelland

MacManus

Zachos

et al. 2020

Journal of Propulsion and Power

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For some embedded engine arrangements, the nature of the inlet distortion is influenced by the boundary layer characteristics at the inlet plane of the intake. This research presents the first quantitative assessment on the influence of inlet boundary layer thickness and asymmetry on the swirl distortion at the exit of an S-shaped intake. Measurements of high spatial and temporal resolution have been acquired at the outlet plane of the S-duct using time-resolved particle image velocimetry. When boundary layer profiles typical of embedded engines are introduced, the characteristic secondary flows at the outlet plane are intensified. Overall, the peak swirl intensity increases by 40% for a boundary layer which is 7 times thicker than the reference case. The unsteady modes of the S-duct remain, although the dominant fluctuations in the flow arise at a frequency 50% lower. When the inlet boundary layer profile becomes asymmetric about the intake centerline the peak swirl events at the hub are reduced by up to 40%. At the tip the peak swirl intensity increases by 29%. The results demonstrate that the effects of inlet boundary layer thickness and asymmetry must be carefully considered as part of engine compatibility tests for complex intakes. Nomenclature ai(t) = Temporal coefficient for i th mode in Proper Orthogonal Decomposition [ms -1 ] Ain = S-duct inlet plane area [m 2 ] Aout = S-duct outlet plane area [m 2 ] Din = S-duct inlet plane diameter [m]

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Section: Iintroductionsupporting

confidence: 60%

Section: Modal Decompositionmentioning

confidence: 88%

Influence of Upstream Total Pressure Profiles on S-Duct Intake Flow Distortion

McLelland

MacManus

Zachos

et al. 2020

Journal of Propulsion and Power

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“…The switching mode promoted the swirl-switching mechanism, by which one of the Dean vortices observed in the mean flow alternately dominates the flowfield [17]. The swirl-switching mode was previously observed by Kalpakli Vester et al [18], who used time-resolved SPIV for the measurement of the airflow velocity field downstream a 90 deg nondiffusing bend for two geometries with different curvature ratios of γ 0.14 and γ 0.39, at Re D 2.3 × 10 4 . The associated modal distribution for the streamwise velocity resembled the lateral perturbation reported by MacManus et al [15] for the total pressure field and represented a lateral modulation of the primary loss region, which followed the movement of the dominant vortex [16].…”

mentioning

confidence: 55%

“…Coherent structures are large-scale flow features that often account for most of the essential flow mechanisms [25]. The POD permits the identification of the most-energetic coherent structures of the flowfield [26] and has been applied in a wide range of applications including the flow in curved pipes [18] and S-ducts [16,27]. The POD of the velocity vector field V, finds an orthonormal set of bases…”

Section: Proper Orthogonal Decompositionmentioning

confidence: 99%

Delayed Detached-Eddy Simulation and Particle Image Velocimetry Investigation of S-Duct Flow Distortion

et al. 2017

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The dynamic flow distortion generated within convoluted aeroengine intakes can affect the performance and operability of the engine. There is a need for a better understanding of the main flow mechanisms that promote flow distortion at the exit of S-shaped intakes. This paper presents a detailed analysis of the main coherent structures in an S-duct flowfield based on a delayed detached-eddy simulation. The capability of this numerical approach to capture the characteristics of the highly unsteady flowfield is demonstrated against high-resolution, synchronous stereoscopic particle image velocimetry measurements at the aerodynamic interface plane. The flowfield mechanisms responsible for the main perturbations at the duct outlet are identified. Clockwise and counterclockwise streamwise vortices are alternately generated around the separation region at a frequency of St 0.53, which promote the swirl switching at the duct outlet. Spanwise vortices are also shed from the separation region at a frequency of St 1.06 and convect downstream along the separated centerline shear layer. This results in a vertical modulation of the main loss region and a fluctuation of the velocity gradient between the high-and low-velocity flow at the aerodynamic interface plane.

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“…Proper Orthogonal Decomposition (POD) has been widely utilised to extract dominant flow features and ultimately coherent structures 29 . The POD has been recently applied for the analysis of turbulent flows in different applications, such as the flow in a backward-facing step 29,30 , reciprocating internal combustion engines 31 , turbulent boundary layers 32 and curved pipes 33 .A detailed mathematical description is beyond the scope of this paper, and only a brief review of the key aspects of the POD is presented. For a more expansive derivation, the reader is referred to…”

Section: Pod Methodsmentioning

confidence: 99%

Complex Aeroengine Intake Ducts and Dynamic Distortion

et al. 2017

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For many embedded engine systems, the intake duct geometry introduces flow distortion and unsteadiness which must be understood when designing the turbomachinery components. The aim of this work is to investigate the capabilities of modern computational methods for these types of complex flows, to study the unsteady characteristics of the flow field and to explore the use of proper orthogonal decomposition methods to understand the nature of the unsteady flow distortion. The unsteady flows for a range of S-duct configurations have been simulated using a delayed detached eddy simulation method. Analysis of the conventional distortion criteria highlights the main sensitivities to the S-duct configuration and quantifies the unsteady range of these parameters. The unsteady flow field shows signature regions of unsteadiness which are postulated to be related to the classical secondary flows as well as to the streamwise flow separation. A proper orthogonal decomposition of the total pressure field at the duct exit identifies the underpinning flow modes which are associated with the overall total pressure unsteadiness distributions. Overall, the unsteady distortion metrics are not found to be solely linked to a particular proper orthogonal decomposition mode, but are dependent on a wider range of modes. Nomenclature p = static pressure p o = total pressure r = cross section radius peak = maximum value of a temporal distribution max = maximum value of a spatial distribution 1

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POD analysis of the turbulent flow downstream a mild and sharp bend

Cited by 39 publications

References 36 publications

Influence of Upstream Total Pressure Profiles on S-Duct Intake Flow Distortion

Influence of Upstream Total Pressure Profiles on S-Duct Intake Flow Distortion

Delayed Detached-Eddy Simulation and Particle Image Velocimetry Investigation of S-Duct Flow Distortion

Complex Aeroengine Intake Ducts and Dynamic Distortion

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