scholarly journals A Study on the Instantaneous Turbulent Flow Field in a 90-Degree Elbow Pipe with Circular Section

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Shiming Wang ◽  
Cheng Ren ◽  
Yangfei Sun ◽  
Xingtuan Yang ◽  
Jiyuan Tu
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Flow Separation ◽  
Large Scale ◽  
Small Scale ◽  
Eddy Simulation ◽  
Dean Vortex ◽  
Instantaneous Flow Field ◽  
Instantaneous Pressure ◽  
Turbulent Flow Field

Based on the special application of 90-degree elbow pipe in the HTR-PM, the large eddy simulation was selected to calculate the instantaneous flow field in the 90-degree elbow pipe combining with the experimental results. The characteristics of the instantaneous turbulent flow field under the influence of flow separation and secondary flow were studied by analyzing the instantaneous pressure information at specific monitoring points and the instantaneous velocity field on the cross section of the elbow. The pattern and the intensity of the Dean vortex and the small scale eddies change over time and induce the asymmetry of the flow field. The turbulent disturbance upstream and the flow separation near the intrados couple with the vortexes of various scales. Energy is transferred from large scale eddies to small scale eddies and dissipated by the viscous stress in the end.

Assessment of large-eddy simulation feasibility in modelling the unsteady diesel fuel injection and mixing in a highspeed direct-injection engine

2009 ◽  
Vol 223 (8) ◽  
pp. 1033-1048 ◽  
Author(s):  
K Jagus ◽  
X Jiang ◽  
G Dober ◽  
G Greeves ◽  
N Milanovic ◽  
...  
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Diesel Fuel ◽  
Fuel Injection ◽  
Direct Injection ◽  
Mesh Size ◽  
Eddy Simulation ◽  
Injection Process ◽  
Mesh Density ◽  
Turbulent Flow Field

This paper aims to assess the feasibility of largeeddy simulation LES as applied to a real engine configuration. Two cases of LES were performed together with a reference Reynoldsaveraged NavierStokes RANS simulation to study their performances in the prediction of the fuel injection and mixing in a highspeed directinjection diesel engine. In addition, sensitivity of the LES results with respect to mesh resolution was investigated, as LES requires a higher mesh density and the filtering process depends on the mesh size. The LES meant that detailed information could be obtained on the fuel spray development and turbulent flow field that was not possible to capture using the RANS modelling approach. It was found that the LES captures flow structures that have a pronounced impact on the prediction of the fuel injection and mixing. Highresolution LES predicted higher liquid and vapour penetration into the cylinder, which is in better agreement with the experimental data obtained at Delphi Diesel Systems than is the RANS prediction. It was also shown that using a finer mesh in LES yields improvements in turbulent flow field prediction, at the same time reducing contribution of the modelled part of the turbulent kinetic energy. Overall, it was proved that LES is a superior alternative to the traditional RANS approach for turbulent twophase flows encountered in diesel fuel injections where flow unsteadiness is prominent. Improved predictions obtained from an advanced LES can subsequently enhance the understanding of the fuel injection process and assist the engine experimentation and design.

Heterogeneous Drag Reduction Concepts and Consequences

1998 ◽  
Vol 120 (4) ◽  
pp. 818-823 ◽  
Author(s):  
Klaus W. Hoyer ◽  
Albert Gyr
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Polymer Solution ◽  
Large Scale ◽  
Scale Interaction ◽  
Polymer Molecules ◽  
Pipe Flows ◽  
Heterogeneous Drag Reduction ◽  
Turbulent Flow Field

This paper deals with the nature of the heterogeneous drag reduction which occurs in turbulent pipe flows when a concentrated polymer solution is injected into the pipe center. According to earlier concepts, the achieved drag reduction is due to a direct, large-scale interaction of the viscoelastic polymer thread with the turbulent flow field. The authors prove that the heterogeneous drag reduction originates exclusively from agglomerates of dissolved polymer molecules present in the flow.

Numerical Investigation of Intermittent Corner Separation in a Linear Compressor Cascade

2016 ◽  
Author(s):  
Wei Ma ◽  
Feng Gao ◽  
Xavier Ottavy ◽  
Lipeng Lu ◽  
A. J. Wang
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Leading Edge ◽  
Suction Side ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Eddy Simulation ◽  
Linear Compressor Cascade

Recently bimodal phenomenon in corner separation has been found by Ma et al. (Experiments in Fluids, 2013, doi:10.1007/s00348-013-1546-y). Through detailed and accurate experimental results of the velocity flow field in a linear compressor cascade, they discovered two aperiodic modes exist in the corner separation of the compressor cascade. This phenomenon reflects the flow in corner separation is high intermittent, and large-scale coherent structures corresponding to two modes exist in the flow field of corner separation. However the generation mechanism of the bimodal phenomenon in corner separation is still unclear and thus needs to be studied further. In order to obtain instantaneous flow field with different unsteadiness and thus to analyse the mechanisms of bimodal phenomenon in corner separation, in this paper detached-eddy simulation (DES) is used to simulate the flow field in the linear compressor cascade where bimodal phenomenon has been found in previous experiment. DES in this paper successfully captures the bimodal phenomenon in the linear compressor cascade found in experiment, including the locations of bimodal points and the development of bimodal points along a line that normal to the blade suction side. We infer that the bimodal phenomenon in the corner separation is induced by the strong interaction between the following two facts. The first is the unsteady upstream flow nearby the leading edge whose angle and magnitude fluctuate simultaneously and significantly. The second is the high unsteady separation in the corner region.

Turbulent flow between counter-rotating concentric cylinders: a direct numerical simulation study

2008 ◽  
Vol 615 ◽  
pp. 371-399 ◽  
Author(s):  
S. DONG
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Outer Cylinder ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Taylor Vortex ◽  
Small Scale ◽  
Mean Flow ◽  
Concentric Cylinders ◽  
High Reynolds

We report three-dimensional direct numerical simulations of the turbulent flow between counter-rotating concentric cylinders with a radius ratio 0.5. The inner- and outer-cylinder Reynolds numbers have the same magnitude, which ranges from 500 to 4000 in the simulations. We show that with the increase of Reynolds number, the prevailing structures in the flow are azimuthal vortices with scales much smaller than the cylinder gap. At high Reynolds numbers, while the instantaneous small-scale vortices permeate the entire domain, the large-scale Taylor vortex motions manifested by the time-averaged field do not penetrate a layer of fluid near the outer cylinder. Comparisons between the standard Taylor–Couette system (rotating inner cylinder, fixed outer cylinder) and the counter-rotating system demonstrate the profound effects of the Coriolis force on the mean flow and other statistical quantities. The dynamical and statistical features of the flow have been investigated in detail.

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