Analysis of Vortical Flow Field in a Propeller Fan by LDV Measurements and LES—Part II: Unsteady Nature of Vortical Flow Structures Due to Tip Vortex Breakdown

2001 ◽  
Vol 123 (4) ◽  
pp. 755-761 ◽  
Author(s):  
Choon-Man Jang ◽  
Masato Furukawa ◽  
Masahiro Inoue
Keyword(s):  
Vortex Breakdown ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Vortex Structures ◽  
Tip Vortex ◽  
Vortical Flow ◽  
Small Scale ◽  
Pressure Surface ◽  
Eddy Simulation ◽  
Cyclic Movements

The unsteady nature of vortex structures has been investigated by a large eddy simulation (LES) in a propeller fan with a shroud covering only the rear region of its rotor tip. The simulation shows that the tip vortex plays a major role in the structure and unsteady behavior of the vortical flow in the propeller fan. The spiral-type breakdown of the tip vortex occurs near the midpitch, leading to significant changes in the nature of the tip vortex. The breakdown gives rise to large and cyclic movements of the tip vortex, so that the vortex impinges cyclically on the pressure surface of the adjacent blade. The movements of the tip vortex cause the leading edge separation vortex to oscillate in a cycle, but on a small scale. The movements of the vortex structures induce high-pressure fluctuations on the rotor blade and in the blade passage.

Flow Structure Above Stationary and Oscillating Low-Aspect-Ratio Wing

2012 ◽  
Author(s):  
Miguel R. Visbal ◽  
Daniel J. Garmann
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Structure ◽  
Large Scale ◽  
Lift Coefficient ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Tip Vortex ◽  
Eddy Simulation ◽  
Moderate Reynolds Number

Computations have been carried out in order to describe the complex unsteady flow structure over a stationary and plunging aspect-ratio-two wing under low Reynolds number conditions (Rec = 104). The flow fields are computed employing a high-fidelity implicit large-eddy simulation (ILES) approach found to be effective for moderate Reynolds number flows exhibiting mixed laminar, transitional and turbulent regions. The evolution of the flow structure and aerodynamic loading as a function of increasing angle of attack is presented. Lift and pressure fluctuations are found to be primarily dominated by the large scale circulatory pattern established above the wing due to separation from the leading edge, and by the inherent three dimensionality of the flow induced by the finite aspect ratio. The spanwise distribution of the sectional lift coefficient revealed only a minor direct contribution to the loading exherted by the tip vortex. High-frequency, small-amplitude oscillations are shown to have a significant effect on the separation process and accompanying loads suggesting potential flow control through either suitable actuation or aero-elastic tailoring.

Detached Eddy Simulation of Unsteady Flow Field and Prediction of Aerodynamic Sound in a Half-Ducted Propeller Fan

2011 ◽  
Author(s):  
K. Kusano ◽  
J. H. Jeong ◽  
K. Yamada ◽  
M. Furukawa
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Tip Vortex ◽  
Vortical Flow ◽  
Detached Eddy Simulation ◽  
Acoustic Analogy ◽  
Aerodynamic Sound ◽  
Pressure Surface ◽  
Eddy Simulation ◽  
Ducted Propeller

Three-dimensional structures and unsteady nature of vortical flow fields in a half ducted propeller fan have been investigated by a detached eddy simulation (DES) based on k-ω two-equation turbulence model. The validity of the numerical simulation performed in the present study was demonstrated by the comparison to LDV measurement results. The simulation shows the tip vortex is so strong that it dominates the flow field near the rotor tip. The tip vortex does not impinge on the pressure surface of the adjacent blade directly, however it interacts with the shroud surface and induces a separation vortex on the shroud. Furthermore, this separation vortex interacts with the pressure surface of the adjacent blade. These flow structures cause high pressure fluctuation on the shroud surface and the blade pressure surface. Besides, sound pressure levels were predicted by Ffowcs William-Hawkings equation based on Lighthill’s acoustic analogy using the unsteady surface pressure data obtained by DES. As a result, the degree of contribution by each flow structure to overall sound has been estimated quantitatively.

scholarly journals Noise characteristic analysis and sound sources identification for rod–airfoil interaction using different subgrid-scale models

2021 ◽  
Vol 233 ◽  
pp. 04036
Author(s):  
Chenghao Yang ◽  
Heying Feng ◽  
Yehui Peng
Keyword(s):  
Energy Transport ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Scale Model ◽  
Subgrid Scale ◽  
Characteristic Analysis ◽  
Sound Sources ◽  
Eddy Simulation ◽  
Scale Models ◽  
The Impact

Four subgrid-scale models based on large eddy simulation (LES), such as Smagorinsky–Lilly (SL), dynamic Smagorinsky–Lilly (DSL), wall-adapting local eddy-viscosity (WALE), and dynamic kinetic-energy transport (KET) were used and couple Ffowcs Williams–Hawkings equation to accurately analyze and identify the characteristics and position of the sound sources of rod–airfoil interaction. The results of four models were compared with experimental data. It was found that the DSL model was the optimal subgrid-scale model for the study of the interaction noise considering the calculation accuracy. Therefore, the DSL model was selected for analyzing and identifying the characteristics and location of the interaction noise source. During the calculation, solid and permeable data surfaces were used for acoustic integral surfaces. The results show that the impact of the quadrupole source is negligible at a low Mach number, and the dipole noise coming from the pressure fluctuations is dominant. Meanwhile, the dipole noise from the airfoil is louder than that from the rod; the leading edge of about 30% chord length of airfoil the is the main sound source of interference effect. Above results can provide guidance for research of blade-vortex interaction noise.

scholarly journals Experimental investigation of a rotor blade tip vortex pair

2021 ◽  
Author(s):  
Dominic Schröder ◽  
Jorge Aguilar-Cabello ◽  
Thomas Leweke ◽  
Ralf Hörnschemeyer ◽  
Eike Stumpf
Keyword(s):  
Water Channel ◽  
Vortex Pair ◽  
Tip Vortex ◽  
Small Scale ◽  
Pressure Surface ◽  
Vortex Interactions ◽  
Rotating Blade ◽  
Blade Tip ◽  
Pair Generation ◽  
Helical Geometry

AbstractThis paper presents the results of an experimental study of two closely spaced vortices generated by a rotating blade with a modified tip geometry. The experiments are carried out in two water channel facilities and involve a generic one-bladed rotor operating in a regime near hover. It is equipped with a parametric fin placed perpendicular to the pressure surface near the tip, which generates a co-rotating vortex pair having a helical geometry. Based on previous results obtained with a fixed wing, a series of small-scale experiments is first carried out, to validate the method of vortex pair generation also for a rotating blade, and to obtain a qualitative overview of its evolution going downstream. A more detailed quantitative study is then performed in a larger facility at three times the initial scale. By varying the fin parameters, it was possible to obtain a configuration in which the two vortices have almost the same circulation. In both experiments, the vortex pair is found to merge into a single helical wake vortex within one blade rotation. Particle image velocimetry measurements show that the resulting vortex has a significantly larger core radius than the single tip vortex from a blade without fin. This finding may have relevance in the context of blade–vortex interactions, where noise generation and fatigue from fluid–structure interactions depend strongly on the vortex core size.

Investigation of Wire Effect in a Wire-Wrapped 37-Pin Fuel Assembly

2015 ◽  
Author(s):  
Jae-Ho Jeong ◽  
Jin Yoo ◽  
Kwi-Lim Lee ◽  
Kwi-Seok Ha
Keyword(s):  
Fuel Assembly ◽  
Relative Position ◽  
Large Scale ◽  
Vortex Structures ◽  
Secondary Flows ◽  
Vortical Flow ◽  
Small Scale ◽  
Multi Scale ◽  
Duct Wall ◽  
The Wire

The wire effect in a wire-wrapped 37-pin fuel assembly mock-up of a Japanese loop-type sodium-cooled fast reactor (SFR), Monju, has been investigated through a numerical analysis using a general-purpose commercial computational fluid dynamics (CFD) code, CFX. Complicated and vortical flow phenomena in the wire-wrapped 37-pin fuel assembly were captured by a Reynolds-Averaged Navier-Stokes (RANS) flow simulation with a shear stress transport (SST) turbulence model. The CFD results show good agreement with Rehme’s friction factor correlation model, which can consider the number of wire-wrapped pins in the fuel assembly. Three-dimensional multi-scale vortex structures start to be formed by an interaction between secondary flows around each wire-wrapped pin. Large-scale and small-scale vortex structures are generated in the corner and edge, and interior sub-channel, respectively. The behavior of the large-scale vortex structures in the corner and edge sub-channel are closely related to the relative position between the hexagonal duct wall and the wire spacer. Regardless of the relative position between the adjacent rod and wire spacer, a small-scale vortex is axially developed in the interior sub-channels. Furthermore, a driving force on each wire spacer surface is closely related to the relative position between the hexagonal duct wall and wire spacer. It is expected that the multi-scale vortex structures in the fuel assembly play a significant role in the convective heat transfer characteristics.

Computational investigation and passive control of vehicle sunroof buffeting

2019 ◽  
Vol 26 (9-10) ◽  
pp. 747-756
Author(s):  
Yansong He ◽  
Quanzhou Zhang ◽  
Changfa An ◽  
Yong Wang ◽  
Zhongming Xu ◽  
...  
Keyword(s):  
Flow Field ◽  
Passive Control ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
The Road ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Utility Vehicle

A computational fluid dynamics simulation method based on large eddy simulation is presented and applied to compute the sunroof buffeting of a sport utility vehicle. The simulation result, i.e. the buffeting level curve, coincides well with the road test. The simulation method is then employed to investigate the sunroof buffeting of a vehicle during the development process in the range of 30 km/h–90 km/h. The results show that the most severe sunroof buffeting occurs at 70 km/h, which corresponds to the resonant frequency of the cabin. Flow field visualizations reveal that strong pressure fluctuations are generated inside the cabin due to vortex shedding from the leading edge and impinging onto the trailing edge of the sunroof opening, which explains the mechanism of sunroof buffeting. A new deflector with a gap and a notched upper edge is designed to replace the original castle type deflector. The simulation results show that the newly designed deflector can reduce the buffeting level to 97.9 dB; that is, the sunroof buffeting is completely eliminated. Moreover, the phenomenon of sunroof buffeting reduction is explained by comparing and analyzing the flow field between the newly designed deflector and the original deflector.

A Study of a Modern Transonic Fan Rotor in a Low Reynolds Number Regime for a Small Turbofan Engine

2013 ◽  
Author(s):  
Toyotaka Sonoda ◽  
Rainer Schnell ◽  
Toshiyuki Arima ◽  
Giles Endicott ◽  
Eberhard Nicke
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Turbofan Engine ◽  
Pressure Surface ◽  
Low Reynolds ◽  
High Reynolds ◽  
Transonic Fan

In this paper, Reynolds effects on a modern transonic low-aspect-ratio fan rotor (Baseline) and the re-designed (optimized) rotor performance are presented with application to a small turbofan engine. The re-design has been done using an in-house numerical optimization system in Honda and the confirmation of the performance was carried out using DLR’s TRACE RANS stage code, assessed with respect to experimental data obtained from a small scale compressor rig in Honda. The baseline rotor performance is evaluated at two Reynolds number conditions, a high Reynolds condition (corresponding to a full engine scale size) and a low Reynolds number condition (corresponding to the small scale compressor rig size), using standard ISA conditions. The performance of the optimized rotor was evaluated at the low Reynolds number condition. The CFD results show significant discrepancies in the rotor efficiency (about 1% at cruise) between these two points due to the different Reynolds numbers. The optimized rotor’s efficiency is increased compared to the baseline. A unique negative curvature region close to the leading edge on the pressure surface of the optimized rotor is one of the reasons why the optimized rotor is superior to the baseline.

POD and Extended-POD Analysis of Pressure Fluctuations and Vortex Structures Inside a Steam Turbine Control Valve

2018 ◽  
Author(s):  
Peng Wang ◽  
Hongyu Ma ◽  
Yingzheng Liu
Keyword(s):  
Steam Turbine ◽  
Pressure Fluctuation ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Turbulence Models ◽  
Control Valve ◽  
Vortex Structures ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Pod Analysis

In steam turbine control valves, pressure fluctuations coupled with vortex structures in highly unsteady three-dimensional flows make essential contributions to aerodynamic forcing on the valve components, and are major sources of flow-induced vibration and acoustic effects. Advanced turbulence models, such as scale adaptive simulation (SAS), detached eddy simulation (DES) and large eddy simulation (LES), can capture detailed flow information of the control valve, but it is challenging to identify the primary flow structures due to the massive flow database. The present study used state-of-the-art data-driven analysis, namely proper orthogonal decomposition (POD) and extended-POD, to extract the energetic pressure fluctuations and dominant vortex structures of the control valve. To this end, the typical annular attachment flow inside a steam turbine control valve was investigated by performing a DES study. Subsequently, the energetic pressure fluctuation modes were extracted by performing POD analysis on the valve’s pressure field. The vortex structures contributing to these energetic pressure fluctuation modes were extracted by performing extended-POD analysis on the pressure-velocity coupling field. Finally, the dominant vortex structures were revealed directly by POD analysis of the valve’s velocity field. The results demonstrated that the flow instabilities inside the control valve were mainly induced by oscillations of the annular wall-attached jet and the derivative flow separations and reattachments. In POD analysis of the pressure field, the axial, antisymmetric and asymmetric pressure modes occupied most of the pressure fluctuation intensity. By further conducting extended-POD analysis, the vortex structures’ incorporation with the energetic pressure modes was identified as mainly attributed to the synchronous, alternating and single-sided oscillation behaviors of the annular attachment flow. However, based on POD analysis of the unsteady velocity fields, the vortex structures, buried in the dominant modes at St = 0.017, were found to result from alternating oscillations of the annular wall-attached jet.

Analysis of Vortical Flow Field in a Propeller Fan by LDV Measurements and LES—Part I: Three-Dimensional Vortical Flow Structures

2001 ◽  
Vol 123 (4) ◽  
pp. 748-754 ◽  
Author(s):  
Choon-Man Jang ◽  
Masato Furukawa ◽  
Masahiro Inoue
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Leading Edge ◽  
Tip Vortex ◽  
Vortical Flow ◽  
Axial Fan ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Edge Separation

Three-dimensional structures of the vortical flow field in a propeller fan with a shroud covering only the rear region of its rotor tip have been investigated by experimental analysis using laser Doppler velocimetry (LDV) measurements and by numerical analysis using a large eddy simulation (LES) in Part I of the present study. The propeller fan has a very complicated vortical flow field near the rotor tip compared with axial fan and compressor rotors. It is found that three vortex structures are formed near the rotor tip: the tip vortex, the leading edge separation vortex, and the tip leakage vortex. The tip vortex is so strong that it dominates the flow field near the tip. Its formation starts from the blade tip suction side near the midchord. Even at the design condition the tip vortex convects nearly in the tangential direction, thus impinging on the pressure surface of the adjacent blade. The leading edge separation vortex develops close along the tip suction surface and disappears in the rear region of the rotor passage. The tip leakage vortex is so weak that it does not affect the flow field in the rotor.

On the Vortex Breakdown Phenomenon in High Angle of Attack Flows Over Delta Wing Geometries

2014 ◽  
Author(s):  
Eric D. Robertson ◽  
Varun Chitta ◽  
D. Keith Walters ◽  
Shanti Bhushan
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
High Angle ◽  
High Angle Of Attack ◽  
Eddy Simulation ◽  
Wing Model

Using computational methods, an investigation was performed on the physical mechanisms leading to vortex breakdown in high angle of attack flows over delta wing geometries. For this purpose, the Second International Vortex Flow Experiment (VFE-2) 65° sweep delta wing model was studied at a root chord Reynolds number (Recr) of 6 × 106 at various angles of attack. The open-source computational fluid dynamics (CFD) solver OpenFOAM was used in parallel with the commercial CFD solver ANSYS® FLUENT. For breadth, a variety of classic closure models were applied, including unsteady Reynolds-averaged Navier-Stokes (URANS) and detached eddy simulation (DES). Results for all cases are analyzed and flow features are identified and discussed. The results show the inception of a pair of leading edge vortices originating at the apex for all models used, and a region of steady vortical structures downstream in the URANS results. However, DES results show regions of massively separated helical flow which manifests after vortex breakdown. Analysis of turbulence quantities in the breakdown region gives further insight into the mechanisms leading to such phenomena.

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