scholarly journals Numerical Study of the Effects of an Obstacle and its Position in a Curved Channel in a Lock-Exchange Flow

2021 ◽  
Author(s):  
Javad Mohammadi ◽  
Bahareh Pirzadeh ◽  
Gholamreza Azizyan ◽  
Azam Abdollahi
Keyword(s):  
Secondary Flow ◽  
Numerical Study ◽  
Longitudinal Velocity ◽  
Gravity Current ◽  
Secondary Flows ◽  
Exchange Flow ◽  
Complex Flow ◽  
Curved Channel ◽  
Maximum Value ◽  
Head Height

Abstract Researchers have recently shown interest in complex flow patterns, especially the effects of secondary flows, in a curved channel. This paper studied the obstacle effects in a gravity current in a channel with a symmetrical 120° bend using the OpenFoam toolbox and the Realizable k–ε turbulence model for simulation. The models studied included no-obstacle curved channel, curved channel with obstacle in 30° position, curved channel with obstacle in 60° position and curved channel with obstacle in 60° position with increased radius. Results showed that the obstacle directed the concentration towards the banks with its maximum value tending from the outer to the inner bank, especially in the tail. Although the post-obstacle head height did not change, that of the tail did (fell); the tail longitudinal velocity was maximized near the channel bed in areas far from the obstacle, and in the outer bank in areas near it. The secondary flow was so reduced that its lowest and most different pattern was observed around the obstacle. In displacing the latter, if the front was at a certain distance from it, the secondary flow did not change much, but if it was at the channel end, the post-obstacle secondary flow increased as the obstacle neared the lock.

Experimental and Numerical Study on Effects of Turbulence Promoters on Flat Plate Film Cooling

2011 ◽  
Author(s):  
Eiji Sakai ◽  
Toshihiko Takahashi
Keyword(s):  
Flat Plate ◽  
Secondary Flow ◽  
Film Cooling ◽  
Numerical Study ◽  
Secondary Flows ◽  
Temperature Fields ◽  
Main Stream ◽  
Cooling Performance ◽  
Cooling Hole ◽  
Stream Lines

Turbulence promoters such as ribs inside turbine blade coolant channels are used to improve convective cooling but at the same time could influence external film cooling performance. The effects of rib orientation and rib position on film cooling performance are experimentally and numerically studied with a flat plate configuration in which external (main) flow and internal (secondary) flow are oriented perpendicular to each other. In the experiment, temperature fields are measured by thermo-couples varying blowing ratio at constant Reynolds number of main and secondary flows. To obtain detailed information about flow fields, Reynolds Averaged Navier Stokes (RANS) simulation and Detached Eddy Simulation (DES) are also performed using a commercial code Fluent. Temperature measured shows that rib orientation has a strong influence on film effectiveness. With forward-oriented ribs, higher film effectiveness is observed compared to the reference case without ribs. On the contrary with inverse-oriented ribs, lower film effectiveness is observed. The difference comes from the flow structure in the film cooling hole. With the forward-oriented ribs, straight stream lines are observed in the cooling hole, while with the inverse-oriented ribs, helical stream lines are observed. Due to the helical stream lines in the hole, ejection angle of the secondary flow to the main stream becomes large, resulting in so called lift-off and lower film effectiveness.

A Numerical Study of the U-Turn Bend in Return Channel Systems for Multistage Centrifugal Compressors

2005 ◽  
Vol 219 (8) ◽  
pp. 749-756 ◽  
Author(s):  
J. M. Oh ◽  
A Engeda ◽  
M. K. Chung
Keyword(s):  
Velocity Profile ◽  
Secondary Flow ◽  
Numerical Study ◽  
Flow Analysis ◽  
Turbulence Models ◽  
Jet Flow ◽  
Complex Flow ◽  
Centrifugal Compressors ◽  
Return Channel ◽  
Channel Systems

A qualitative numerical study of the flow in the U-turn bend of return channel systems for multistage centrifugal compressors is presented. Calculations have been carried out using the flow analysis program FLUENT. The flow in the U-turn bend is highly three-dimensional and complex. The main cause for this is the circumferential variation of the velocity profile at the inlet of the bend. The circumferential variation of the velocity profile is an unavoidable result from the wake/jet flow at the exit of the impeller. In this article, first the effect of the wake/jet flow coming into the U-turn bend is studied. It is shown that the wake/jet flow develops to form the secondary flow in the U-turn bend. The secondary flow, with the high streamline curvature of the flow in the bend, makes the flow inside the bend highly complex. This complex flow is hard to predict with conventional turbulence models that have been developed on the basis of near homogeneity of flows. Comparing the present result with a study that successfully predicted the loss and flow behaviour in the bend, a discussion is presented on the turbulence and the turbulence models. Also, the loss mechanisms in the U-turn bend are discussed in detail.

scholarly journals Numerical Study of Turbulent Secondary Flows in Curved Ducts

1990 ◽  
Vol 112 (2) ◽  
pp. 205-211 ◽  
Author(s):  
N. Hur ◽  
S. Thangam ◽  
C. G. Speziale
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Cross Section ◽  
Numerical Study ◽  
Secondary Flows ◽  
Fully Developed Turbulent Flow ◽  
Volume Method ◽  
Curved Ducts ◽  
Good Agreement

The pressure driven, fully developed turbulent flow of an incompressible viscous fluid in curved ducts of square cross-section is studied numerically by making use of a finite volume method. A nonlinear K -1 model is used to represent the turbulence. The results for both straight and curved ducts are presented. For the case of fully developed turbulent flow in straight ducts, the secondary flow is characterized by an eight-vortex structure for which the computed flowfield is shown to be in good agreement with available experimental data. The introduction of moderate curvature is shown to cause a substantial increase in the strength of the secondary flow and to change the secondary flow pattern to either a double-vortex or a four-vortex configuration.

scholarly journals Hydrodynamic Characteristics of Flow in a Strongly Curved Channel with Gravel Beds

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1519
Author(s):  
Ying-Tien Lin ◽  
Yu Yang ◽  
Yu-Jia Chiu ◽  
Xiaoyan Ji
Keyword(s):  
Numerical Simulations ◽  
Secondary Flow ◽  
Longitudinal Velocity ◽  
Three Dimensional ◽  
Power Spectra ◽  
Inertial Subrange ◽  
Hydrodynamic Characteristics ◽  
Curved Channel ◽  
Form Drag ◽  
Rough Bed

This study experimentally and numerically investigated the hydrodynamic characteristics of a 180° curved open channel over rough bed under the condition of constant downstream water depth. Three different sizes of bed particles (the small, middle and big cases based upon the grain size diameter D50) were selected for flume tests. Three-dimensional instantaneous velocities obtained by the acoustic Doppler velocimeter (ADV) were used to analyze hydrodynamic characteristics. Additionally, the Renormalization-Group (RNG) turbulence model was employed for numerical simulations. Experimental results show that rough bed strengthens turbulence and increases turbulent kinetic energy along curved channels. The power spectra of the longitudinal velocity fluctuation satisfy the classic Kolmogorov −5/3 law in the inertial subrange, and the existence of rough bed shortens the inertial subrange and causes the flow reach the viscous dissipation range in advance. The contributions of sweeps and ejections are more important than those of the outward and inward interactions over a rough bed for the middle case. Flow-3D was adopted to simulate flow patterns on two rough bed settings with same surface roughness (skin drag) but different bed shapes (form drag): one is bed covered with thick bottom sediment layers along the curved part of the flume (the big case) as the experimental condition, and the other one is uniform bed along the entire flume (called the big case_flat only for simulations). Numerical simulations reveal that the secondary flow is confined to the near-bed area and the intensity of secondary flow is improved for both rough bed cases, possibly causing more serious bed erosion along a curved channel. In addition, the thick bottom sediments (the big case), i.e., larger form drag, can enhance turbulence strength near bed regions, enlarge the transverse range of secondary flow, and delay the shifting of the core region of maximum longitudinal velocity towards the concave bank.

scholarly journals Impacts of Deformed Bed Topography on Hydrodynamics in a Near-Bank Vegetated Channel: A Numerical Study

2020 ◽  
Author(s):  
Daoxudong Liu ◽  
Wenjun Li
Keyword(s):  
Numerical Study ◽  
Water Discharge ◽  
Longitudinal Velocity ◽  
Leading Edge ◽  
Secondary Flows ◽  
Bed Topography ◽  
Surface Gradient ◽  
Flow Adjustment ◽  
Flow Mixing ◽  
Open Region

Understanding how the deformed bed topography induced by near-bank vegetation impacts the hydrodynamics is significant for understanding the maintenance condition of bed morphology and further fluvial evolution. This issue has rarely been addressed by current studies. This study with a 2D hydro-morphological model investigates the hydrodynamics over flat and deformed beds with a near-bank vegetation patch. By varying the patch density, the generalized results show that the hydrodynamics for the deformed bed differs a lot from those for the flat bed. It is found that deformed bed topography leads to an apparent decrease in longitudinal velocity and bed shear stress in the open region and longitudinal surface gradient for the entire vegetated reach. However, the transverse flow motion and transverse surface gradient in the region of the leading edge and trailing edge is enhanced or maintained, suggesting the strengthening of secondary flows. Interestingly, the deformed bed topography tends to alleviate the turbulent effect caused by the junction-interface horizontal coherent vortices, indicating that the turbulence-induced flow mixing is highly inhibited by the deformed bed. Alternatively, the enhanced secondary flows might provide compensation for the flow mixing for the deformed bed, confirmed by a faster recovery of the redistributed water discharge for the vegetated and open regions to the normal value (50%). The interior flow adjustment through the patch for the deformed bed requires a shorter distance, which links the vegetative drag length with a logarithmic relation. The tilting bed topographic effect in the open region to accelerate the flow may account for the faster flow adjustment.

Volumetric Velocimetry Measurements of Purge-Mainstream Interaction in a 1-Stage Turbine

2020 ◽  
Author(s):  
A. J. Carvalho Figueiredo ◽  
B. D. J. Schreiner ◽  
A. W. Mesny ◽  
O. J. Pountney ◽  
J. A. Scobie ◽  
...  
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Suction Side ◽  
Secondary Flows ◽  
Complex Flow ◽  
Blade Passage ◽  
Passage Vortex ◽  
Purge Flow ◽  
Secondary Flow Field

Abstract Air-cooled gas turbines employ bleed air from the compressor to cool vulnerable components in the turbine. The cooling flow, commonly known as purge air, is introduced at low radius, before exiting through the rim-seal at the periphery of the turbine discs. The purge flow interacts with the mainstream gas path, creating an unsteady and complex flow-field. Of particular interest to the designer is the effect of purge on the secondary flow structures within the blade passage, the extent of which directly affects the aerodynamic loss in the stage. This paper presents a combined experimental and Computational Fluid Dynamics (CFD) investigation into the effect of purge flow on the secondary flows in the blade passage of an optically-accessible 1-stage turbine rig. The experimental campaign was conducted using Volumetric Velocimetry (VV) measurements to assess the three-dimensional inter-blade velocity field; the complementary CFD campaign was carried out using URANS computations. The implementation of VV within a rotating environment is a world first and offers an unparalleled level of experimental detail. The baseline flow-field, in the absence of purge flow, demonstrated a classical secondary flow-field: the roll-up of a horseshoe-vortex, with subsequent downstream convection of a pressure-side and suction-side leg, the former transitioning in to the passage vortex. The introduction of purge, at 1.7% of the mainstream flow-rate, was shown to modify the secondary flow field by enhancing the passage vortex, both in strength and span-wise migration. The computational predictions were in agreement with the enhancement revealed by the experiments.

A Numerical Study of Secondary Flows in a 1.5 Stage Axial Turbine Guiding the Design of a Non-Axisymmetric Hub

2017 ◽  
Author(s):  
Hayder M. B. Obaida ◽  
Hakim T. K. Kadhim ◽  
Aldo Rona ◽  
Katrin Leschke ◽  
J. Paul Gostelow
Keyword(s):  
Secondary Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Axial Flow ◽  
Suction Side ◽  
Side Branch ◽  
Secondary Flows ◽  
Design Work ◽  
Axial Turbine ◽  
Turbine Performance

The performance of axial flow turbines is affected by losses from secondary flows that result in entropy generation. Reducing these secondary flow losses improves the turbine performance. This paper investigates the effect of applying a non-axisymmetric contour to the hub of a representative one-and-half stage axial turbine on the turbine performance. An analytical end-wall hub surface definition with a guide groove is used to direct the pressure side branch of the horseshoe vortex away from the blade suction side, so to retard its interaction with the suction side secondary flow and thus decrease the losses. This groove design is a development of the concept outlined in Obaida et al. (2016). A baseline three-dimensional steady RANS k-ω SST model, with axisymmetric walls, is validated against reference experimental measurements from a one-and-half stage turbine at the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen, Germany. The CFD predictions of the non-axisymmetric hub with the guide groove show a decrease in the total pressure loss coefficient. The design work-flow is generated using the Alstom Process and Optimisation Workbench (APOW), which sensibly reduced the designer workload. The implementation of the guide groove has excellent portability to the turbomachinery industry and this makes this method promising for delivering the UK energy agenda through more efficient power turbines.

Numerical Study of the Thermal Development in a Rotating Cooling Passage

2008 ◽  
Author(s):  
Jose Martinez Lucci ◽  
R. S. Amano ◽  
Krishna Guntur ◽  
B. Song
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Turbulence Models ◽  
Outer Wall ◽  
Reynolds Stress Model ◽  
Secondary Flows ◽  
Complex Flow ◽  
Rotation Numbers ◽  
Thermal Development ◽  
Cooling Passage

In the present study, the fully developed turbulent secondary flows inside rotating square-upstream section and rectangular downstream section oriented at several angles with axis rotation are numerically simulated using the low Reynolds Non-linear k–ω, k–ε Reynolds-Stress Model (RSM), and Large Eddy Simulation (LES) models. The two flat walls are heated (leading and trailing sides), while the outer wall and the splitter plate are thermally insulated. The simulation has been done at Re = 36000 with different rotation numbers from Ro = −0.4 to Ro = 0.4, where negative Ro values refer to counter-clock wise and positive Ro values refer to clock wise sense of rotation. This enables to investigate the effects on the thermal development of the rotation numbers. The effects of minor modifications, in cross section area at the bend exit, on thermal development, under rotating conditions, can also be explored. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. Previous studies have shown that the flow and heat transfer features through curved bends, even with a moderate curvature, cannot be accurately simulated. It is the conventional belief and practice that the usage of a proper turbulence model and a reliable numerical method for achieving accurate computations. It is shown that the present RSM model produces satisfactory predictions of the flow development inside the sharp U-bend comparing with the experiments [1]. In the present study, three turbulence models are used to predict Nusselt number distribution. The results were further compared with the LES computations and discussed the difference between the turbulence models and the LES as well.

scholarly journals Secondary Flow and Heat Transfer Coefficient Distributions in the Developing Flow Region of Ribbed Turbine Blade Cooling Passages

2014 ◽  
Author(s):  
Peter R. Forsyth ◽  
Matthew McGilvray ◽  
David R. H. Gillespie
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Numerical Simulations ◽  
Secondary Flow ◽  
Numerical Study ◽  
Secondary Flows ◽  
Local Flow ◽  
Flow And Heat Transfer ◽  
Cooling Passage

This paper reports an experimental and numerical study of the development and coupling of aerodynamic flows and heat transfer within a model ribbed internal cooling passage to provide insight into the development of secondary flows. Static instrumentation was installed at the end of a long smooth passage, and used to measure local flow features in a series of experiments where ribs were incrementally added upstream. This improves test turnaround time while ensuring that the aerodynamic probe was non-invasive. Local heat transfer coefficient distributions were similarly captured using a hybrid transient liquid crystal technique. A composite heat transfer coefficient distribution for a 12 rib-pitch passage is reported: notably the behaviour is dominated by the development of the secondary flow in the passage throughout. Both the aerodynamic and heat transfer test data were compared to numerical simulations developed using a commercial computational fluid dynamics solver. By conducting a number of simulations it was possible to interrogate the validity of the underlying assumptions of the experimental strategy — their validity is discussed. The results capture the developing size and strength of the vortical structures in secondary flow. The local flow field was sensibly shown to be strongly coupled to the enhancement of heat transfer coefficient. Comparison of the experimental and numerical data generally show excellent agreement in the level of heat transfer coefficient predicted, though the numerical simulations fail to capture some local enhancement on the ribbed surfaces. Where this was the case the coupled flow and heat transfer measurements were able to identify missing velocity field characteristics.

Laminar Mixed Convection in a Concentric Annulus With Horizontal Axis

1985 ◽  
Vol 107 (4) ◽  
pp. 902-909 ◽  
Author(s):  
A. O. Nieckele ◽  
S. V. Patankar
Keyword(s):  
Rayleigh Number ◽  
Secondary Flow ◽  
Cross Section ◽  
Numerical Study ◽  
Secondary Flows ◽  
Cross Sectional ◽  
Laminar Mixed Convection ◽  
The Cross ◽  
Annular Pipe ◽  
Rayleigh Numbers

Axial laminar flow in a horizontal annular pipe is influenced by the presence of buoyancy-induced secondary flows that are caused by the heat flow from the inner cylinder. A numerical study is presented for the fully developed region of the buoyancy-affected flow. The distributions of the axial and cross-sectional velocities are calculated along with the temperature variation in the cross section. Results are presented for a range of values of the Rayleigh number, the Prandtl number, and the radius ratio of the annulus. The Nusselt number increases significantly with the Rayleigh number; yet the corresponding increase in the friction factor is found to be rather small. Distributions of secondary flow and isotherms over the cross section are presented for different values of the parameters. In each half of the annulus on either side of the vertical centerline, the secondary flow displays a single-eddy pattern at low Rayleigh numbers and changes to a double-eddy pattern at high values.

Sign in / Sign up

Export Citation Format

Share Document