Secondary flows in ducts of square cross-section

1972 ◽  
Vol 54 (2) ◽  
pp. 289-295 ◽  
Author(s):  
B. E. Launder ◽  
W. M. Ying
Keyword(s):  
Secondary Flow ◽  
Cross Section ◽  
Experimental Research ◽  
Friction Velocity ◽  
Rough Surfaces ◽  
Axial Flow ◽  
Secondary Flows ◽  
Main Emphasis

The paper presents the outcome of experimental research on turbulence-induced secondary flows in square-sectioned ducts. The main emphasis of the experiments has been on the measurement of the secondary flows in a duct with equally roughened surfaces. Here the secondary flow is a substantially larger proportion of the axial flow than is the case in smooth-walled ducts. With the secondary velocities normalized by the friction velocity, however, the resultant profiles for smooth and rough surfaces are the same, within the precision of the measurements.

scholarly journals A Review of Numerical Simulations of Secondary Flows in River Bends

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 884
Author(s):  
Rawaa Shaheed ◽  
Abdolmajid Mohammadian ◽  
Xiaohui Yan
Keyword(s):  
Numerical Modeling ◽  
Numerical Simulations ◽  
Secondary Flow ◽  
Cross Section ◽  
Turbulence Models ◽  
Main Flow ◽  
Secondary Flows ◽  
River Bends ◽  
River Cross Section ◽  
River Bend

River bends are one of the common elements in most natural rivers, and secondary flow is one of the most important flow features in the bends. The secondary flow is perpendicular to the main flow and has a helical path moving towards the outer bank at the upper part of the river cross-section, and towards the inner bank at the lower part of the river cross-section. The secondary flow causes a redistribution in the main flow. Accordingly, this redistribution and sediment transport by the secondary flow may lead to the formation of a typical pattern of river bend profile. It is important to study and understand the flow pattern in order to predict the profile and the position of the bend in the river. However, there are a lack of comprehensive reviews on the advances in numerical modeling of bend secondary flow in the literature. Therefore, this study comprehensively reviews the fundamentals of secondary flow, the governing equations and boundary conditions for numerical simulations, and previous numerical studies on river bend flows. Most importantly, it reviews various numerical simulation strategies and performance of various turbulence models in simulating the flow in river bends and concludes that the main problem is finding the appropriate model for each case of turbulent flow. The present review summarizes the recent advances in numerical modeling of secondary flow and points out the key challenges, which can provide useful information for future studies.

Predictions of Endwall Losses and Secondary Flows in Axial Flow Turbine Cascades

1987 ◽  
Vol 109 (2) ◽  
pp. 229-236 ◽  
Author(s):  
O. P. Sharma ◽  
T. L. Butler
Keyword(s):  
Flow Visualization ◽  
Secondary Flow ◽  
Axial Flow ◽  
Secondary Flows ◽  
Integral Boundary ◽  
Realistic Interpretation ◽  
Proposed Model ◽  
Flow Theories ◽  
Semi Empirical ◽  
End Wall

This paper describes the development of a semi-empirical model for estimating end-wall losses. The model has been developed from improved understanding of complex endwall secondary flows, acquired through review of flow visualization and pressure loss data for axial flow turbomachine cascades. The flow visualization data together with detailed measurements of viscous flow development through cascades have permitted more realistic interpretation of the classical secondary flow theories for axial turbomachine cascades. The re-interpreted secondary flow theories together with integral boundary layer concepts are used to formulate a calculation procedure for predicting losses due to the endwall secondary flows. The proposed model is evaluated against data from published literature and improved agreement between the data and predictions is demonstrated.

Visualization Study of Flow in Axial Flow Inducer

1972 ◽  
Vol 94 (4) ◽  
pp. 777-787 ◽  
Author(s):  
B. Lakshminarayana
Keyword(s):  
Radial Velocity ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Axial Flow ◽  
Flow Theory ◽  
Secondary Flows ◽  
Flow Coefficient ◽  
Flow Through

A visualization study of the flow through a three ft dia model of a four bladed inducer, which is operated in air at a flow coefficient of 0.065, is reported in this paper. The flow near the blade surfaces, inside the rotating passages, downstream and upstream of the inducer is visualized by means of smoke, tufts, ammonia filament, and lampblack techniques. Flow is found to be highly three dimensional, with appreciable radial velocity throughout the entire passage. The secondary flows observed near the hub and annulus walls agree with qualitative predictions obtained from the inviscid secondary flow theory. Based on these investigations, methods of modeling the flow are discussed.

Secondary Flow, Turbulent Diffusion, and Mixing in Axial-Flow Compressors

1987 ◽  
Vol 109 (4) ◽  
pp. 455-469 ◽  
Author(s):  
D. C. Wisler ◽  
R. C. Bauer ◽  
T. H. Okiishi
Keyword(s):  
Secondary Flow ◽  
Turbulent Diffusion ◽  
Fluid Motion ◽  
Axial Flow ◽  
Secondary Flows ◽  
Tracer Gas ◽  
Order Of Magnitude ◽  
Diffusive Effects ◽  
Experimental Findings ◽  
Axial Flow Compressors

The relative importance of convection by secondary flows and diffusion by turbulence as mechanisms responsible for mixing in multistage, axial-flow compressors has been investigated by using the ethylene tracer-gas technique and hot-wire anemometry. The tests were conducted at two loading levels in a large, low-speed, four-stage compressor. The experimental results show that considerable cross-passage and spanwise fluid motion can occur and that both secondary flow and turbulent diffusion can play important roles in the mixing process, depending upon location in the compressor and loading level. In the so-called freestream region, turbulent diffusion appeared to be the dominant mixing mechanism. However, near the endwalls and along airfoil surfaces at both loading levels, the convective effects from secondary flow were of the same order of magnitude as, and in some cases greater than, the diffusive effects from turbulence. Calculations of the secondary flowfield and mixing coefficients support the experimental findings.

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.

Improving Efficiency of a High Work Turbine Using Non-Axisymmetric Endwalls: Part II—Time-Resolved Flow Physics

2008 ◽  
Author(s):  
P. Schuepbach ◽  
R. S. Abhari ◽  
M. G. Rose ◽  
T. Germain ◽  
I. Raab ◽  
...  
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Guide Vane ◽  
Axial Flow ◽  
Fast Response ◽  
Secondary Flows ◽  
Streamwise Vorticity ◽  
Time Resolved ◽  
Flow Physics ◽  
High Work

This paper is the second part of a two part paper that reports on the improvement of efficiency of a one-and-half stage high work axial flow turbine. The first part covered the design of the endwall profiling as well as a comparison with steady probe data, this part covers the analysis of the time-resolved flow physics. The focus is on the time-resolved flow physics that lead to a total-to-total stage efficiency improvement of Δηtt = 1.0% ± 0.4%. The investigated geometry is a model of a high work (Δh/U2 = 2.36), axial shroudless HP turbine. The time-resolved measurements have been acquired upstream and downstream of the rotor using a Fast Response Aerodynamic Probe (FRAP). The paper contains a detailed analysis of the secondary flow field that is changed between the axisymmetric and the non-axisymmetric endwall profiling cases. The flowfield at exit of the first stator is improved considerably due to non-axisymmetric endwall profiling and results in reduced secondary flow and a reduction of loss at both hub and tip, as well as a reduced trailing shed vorticity. The rotor has reduced losses and a reduction of secondary flows mainly at the hub. At the rotor exit the flow field with non-axisymmetric endwalls is more homogenous due to the reduction of secondary flows in the two rows upstream of the measurement plane. This confirms that non-axisymmetric endwall profiling is an effective tool for reducing secondary losses in axial turbines. Using a frozen flow assumption the time-resolved data is used to estimate the axial velocity gradients, which are then used to evaluate the streamwise vorticity and dissipation. The non-axisymmetric endwall profiling of the first nozzle guide vane show reductions of dissipation and streamwise vorticity due to reduced trailing shed vorticity. This smaller vorticity explains the reduction of loss at mid-span, which is shown in the first part of the two part paper. This leads to the conclusion that non-axisymmetric endwall profiling also has the potential of reducing trailing shed vorticity.

The Influence of Sweep on Axial Flow Turbine Aerodynamics in the Endwall Region

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Graham Pullan ◽  
Neil W. Harvey
Keyword(s):  
Secondary Flow ◽  
Computational Study ◽  
Axial Flow ◽  
Secondary Flows ◽  
Blade Loading ◽  
Stream Surface ◽  
Reported Study ◽  
Secondary Flow Structure ◽  
Turbine Design ◽  
Axisymmetric Stream

Sweep, when the stacking axis of the blade is not perpendicular to the axisymmetric stream surface in the meridional view, is often an unavoidable feature of turbine design. In a previously reported study, the authors demonstrated that sweep leads to an inevitable increase in midspan profile loss. In this paper, the influence on the flowfield close to the endwalls is investigated. Experimental data from two linear cascades, one unswept, and the other swept at 45 deg but having the same overall turning and midspan pressure distribution, are presented. It is shown that sweep causes the blade to become more rear loaded at the hub and fore loaded at the casing. This is further shown to reduce the penetration of the secondary flow at the hub, and to produce a highly unusual secondary flow structure, with low endwall overturning, at the casing. A computational study is then presented in which the development of the secondary flows of both blades is studied. The differences in the endwall flowfields are found to be caused by a combination of the effect of sweep on both the endwall blade loading distribution and on the bulk movements of the primary irrotational flow.

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.

The influence of secondary flows induced by normal stress differences on the shear-induced migration of particles in concentrated suspensions

2008 ◽  
Vol 603 ◽  
pp. 207-243 ◽  
Author(s):  
ARUN RAMACHANDRAN ◽  
DAVID T. LEIGHTON
Keyword(s):  
Normal Stress ◽  
Secondary Flow ◽  
Cross Section ◽  
Concentration Distribution ◽  
Normal Stress Difference ◽  
Secondary Flows ◽  
Stress Difference ◽  
Second Normal Stress Difference ◽  
Normal Stress Differences ◽  
The Cross

It was first demonstrated experimentally by H. Giesekus in 1965 that the second normal stress difference in polymers can induce a secondary flow within the cross-section of a non-axisymmetric conduit. In this paper, we show through simulations that the same may be true for suspensions of rigid non-colloidal particles that are known to exhibit a strong negative second normal stress difference. Typically, the magnitudes of the transverse velocity components are small compared to the average axial velocity of the suspension; but the ratio of this transverse convective velocity to the shear-induced migration velocity is characterized by the shear-induced migration Péclet number χ which scales as B2/a2, B being the characteristic length scale of the cross-section and a being the particle radius. Since this Péclet number is kept high in suspension experiments (typically 100 to 2500), the influence of the weak circulation currents on the concentration profile can be very strong, a result that has not been appreciated in previous work. The principal effect of secondary flows on the concentration distribution as determined from simulations using the suspension balance model of Nott & Brady (J. Fluid Mech. vol. 275, 1994, p. 157) and the constitutive equations of Zarraga et al. (J. Rheol. vol. 44, 2000, p. 185) is three-fold. First, the steady-state particle concentration distribution is no longer independent of particle size; rather, it depends on the aspect ratio B/a. Secondly, the direction of the secondary flow is such that particles are swept out of regions of high streamsurface curvature, e.g. particle concentrations in corners reach a minimum rather than the local maximum predicted in the absence of such flows. Finally, the second normal stress differences lead to instabilities even in such simple geometries as plane-Poiseuille flow.

Spanwise Mixing in Axial-Flow Turbomachines

1982 ◽  
Vol 104 (1) ◽  
pp. 97-110 ◽  
Author(s):  
G. G. Adkins ◽  
L. H. Smith
Keyword(s):  
Secondary Flow ◽  
Boundary Layers ◽  
Axial Flow ◽  
Separated Flow ◽  
Secondary Flows ◽  
Main Stream ◽  
Flow Measurements ◽  
Mixing Coefficient ◽  
Blade Row ◽  
End Wall

Flow measurements taken in multistage axial-flow turbomachines suggest that substantial spanwise mixing of flow properties often occurs. In addition, measured blade row turnings often show considerable deviation from two-dimensional cascade theory, particularly in the end-wall regions. An approximate method is presented with which both of these effects can be included in design through-flow calculations. The method is based on inviscid, small-perturbation secondary flow theory. Frictional effects are not directly included but secondary flows caused by annulus wall and blade boundary layers are included in an approximate way. The secondary flow model includes effects of 1) main-stream nonfree-vortex flow, 2) end-wall boundary layers, 3) blade end clearances, 4) blade end shrouding, and 5) blade boundary layer and wake centrifugation. The spanwise mixing phenomenon is modeled as a diffusion process, where the mixing coefficient is related to the calculated spanwise secondary velocities. Empirical adjustments are employed to account for the dissipation of the secondary velocities and interactions with downstream blade rows. The induced blade row overturnings are related to the calculated cross-passage secondary velocities. The nature of the assumptions employed restricts the method to design-point-type applications for which losses are relatively small and significant regions of separated flow are not present.

Sign in / Sign up

Export Citation Format

Share Document