The Physics of the Secondary Flows of Viscoelastic Fluids in Straight Tubes

2000 ◽  
Author(s):  
Dennis A. Siginer
Keyword(s):  
Secondary Flow ◽  
Cross Sections ◽  
Viscoelastic Fluids ◽  
Secondary Flows ◽  
Novel Approach ◽  
Transversal Field ◽  
Time Domains ◽  
Viscoelastic Liquids ◽  
First Time ◽  
Secondary Flow Field

Abstract A survey of secondary flows of viscoelastic liquids in straight tubes is given including recent work pointing at striking analogies with transversal deformations associated with the simple shearing of solid materials. The importance and implications of secondary flows of viscoelastic fluids in heat transfer enhancement are explored together with the difficulties in detecting weak secondary flows (dilute, weakly viscoelastic solutions) in a laboratory setting. Recent new work by the author and colleagues which explores for the first time the structure of the secondary flow field in the pulsating flow of a constitutively nonlinear simple fluid, whose structure is defined by a series of nested integrals over semi-infinite time domains, in straight tubes of arbitrary cross-sections is summarized. The transversal field arises at the second order of the perturbation of the nonlinear constitutive structure, and is driven by first order terms which define the linearly viscoelastic longitudinal flow in the hierarchy of superposed linear flows stemming from the perturbation of the constitutive structure. Arbitrary conduit contours are obtained through a novel approach to the concept of domain perturbation. Time averaged, mean secondary flow streamline contours are presented for the first time for triangular, square and hexagonal pipes.

The Mechanics of the Secondary Flows of Viscoelastic Fluids in Non-Circular Straight Tubes and the Mean Transversal Field in Pulsating Flows

2000 ◽  
Author(s):  
Dennis A. Siginer ◽  
Mario F. Letelier
Keyword(s):  
Secondary Flow ◽  
Cross Sections ◽  
Viscoelastic Fluids ◽  
Secondary Flows ◽  
Novel Approach ◽  
Transversal Field ◽  
Time Domains ◽  
Viscoelastic Liquids ◽  
First Time ◽  
Secondary Flow Field

Abstract A survey of secondary flows of viscoelastic liquids in straight tubes is given including recent work pointing at striking analogies with transversal deformations associated with the simple shearing of solid materials. The importance and implications of secondary flows of viscoelastic fluids in heat transfer enhancement are explored together with the difficulties in detecting weak secondary flows (dilute, weakly viscoelastic solutions) in a laboratory setting. Recent new work by the author and colleagues which explores for the first time the structure of the secondary flow field in the pulsating flow of a constitutively nonlinear simple fluid, whose structure is defined by a series of nested integrals over semi-infinite time domains, in straight tubes of arbitrary cross-sections is summarized. The transversal field arises at the second order of the perturbation of the nonlinear constitutive structure, and is driven by first order terms which define the linearly viscoelastic longitudinal flow in the hierarchy of superposed linear flows stemming from the perturbation of the constitutive structure. Arbitrary conduit contours are obtained through a novel approach to the concept of domain perturbation. Time averaged, mean secondary flow streamline contours are presented for the first time for triangular, square and hexagonal pipes.

The Physics of the Secondary Flows of Viscoelastic Fluids in Straight Tubes

2000 ◽  
Author(s):  
Dennis A. Siginer
Keyword(s):  
Secondary Flow ◽  
Cross Sections ◽  
Viscoelastic Fluids ◽  
Secondary Flows ◽  
Novel Approach ◽  
Transversal Field ◽  
Time Domains ◽  
Viscoelastic Liquids ◽  
First Time ◽  
Secondary Flow Field

Abstract A survey of secondary flows of viscoelastic liquids in straight tubes is given including recent work pointing at striking analogies with transversal deformations associated with the simple shearing of solid materials. The importance and implications of secondary flows of viscoelastic fluids in heat transfer enhancement are explored together with the difficulties in detecting weak secondary flows (dilute, weakly viscoelastic solutions) in a laboratory setting. Recent new work by the author and colleagues which explores for the first time the structure of the secondary flow field in the pulsating flow of a constitutively nonlinear simple fluid, whose structure is defined by a series of nested integrals over semi-infinite time domains, in straight tubes of arbitrary cross-sections is summarized. The transversal field arises at the second order of the perturbation of the nonlinear constitutive structure, and is driven by first order terms which define the linearly viscoelastic longitudinal flow in the hierarchy of superposed linear flows stemming from the perturbation of the constitutive structure. Arbitrary conduit contours are obtained through a novel approach to the concept of domain perturbation. Time averaged, mean secondary flow streamline contours are presented for the first time for triangular, square and hexagonal pipes.

Review of the Secondary Flows of Complex Fluids

2003 ◽  
Author(s):  
Dennis A. Siginer
Keyword(s):  
Secondary Flow ◽  
Cross Sections ◽  
Secondary Flows ◽  
Laboratory Setting ◽  
Transfer Enhancement ◽  
Domain Perturbation ◽  
Novel Approach ◽  
Viscoelastic Liquids ◽  
First Time ◽  
Secondary Flow Field

A survey of secondary flows of viscoelastic liquids in straight tubes is given including recent work pointing at striking analogies with transversal deformations associated with the simple shearing of solid materials. The importance and implications of secondary flows of viscoelastic fluids in heat transfer enhancement are explored together with the difficulties in detecting weak secondary flows (dilute, weakly viscoelastic solutions) in a laboratory setting. Recent new work by the author and colleagues which explores for the first time the structure of the secondary flow field in the pulsating flow of a constitutively nonlinear simple fluid in straight tubes of arbitrary cross-sections is summarized. Arbitrary conduit contours are obtained through a novel approach to the concept of domain perturbation. Time averaged, mean secondary flow streamline contours are presented for the first time for triangular, square and hexagonal pipes.

scholarly journals Incidence Angle and Pitch-Chord Effects on Secondary Flows Downstream of a Turbine Cascade

1992 ◽  
Author(s):  
A. Perdichizzi ◽  
V. Dossena
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Oil Flow ◽  
Secondary Velocity ◽  
Secondary Flow Field

This paper describes the results of an experimental investigation of the three-dimensional flow downstream of a linear turbine cascade at off-design conditions. The tests have been carried out for five incidence angles from −60 to +35 degrees, and for three pitch-chord ratios: s/c = 0.58,0.73,0.87. Data include blade pressure distributions, oil flow visualizations, and pressure probe measurements. The secondary flow field has been obtained by traversing a miniature five hole probe in a plane located at 50% of an axial chord downstream of the trailing edge. The distributions of local energy loss coefficients, together with vorticity and secondary velocity plots show in detail how much the secondary flow field is modified both by incidence and cascade solidity variations. The level of secondary vorticity and the intensity of the crossflow at the endwall have been found to be strictly related to the blade loading occurring in the blade entrance region. Heavy changes occur in the spanwise distributions of the pitch averaged loss and of the deviation angle, when incidence or pitch-chord ratio is varied.

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

2021 ◽  
Vol 143 (4) ◽  
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 ◽  
Blade Passage ◽  
One Stage ◽  
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 flowfield. 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 one-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 unsteady Reynolds-averaged Navier–Stokes (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 rollup 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 flowrate, was shown to modify the secondary flow-field by enhancing the passage vortex, in both strength and span-wise migration. The computational predictions were in agreement with the enhancement revealed by the experiments.

Flow Visualization of Secondary Flows in Three Curved Ducts

1986 ◽  
Author(s):  
G. M. Sanz ◽  
R. D. Flack
Keyword(s):  
Secondary Flow ◽  
Cross Sections ◽  
Flow Patterns ◽  
Secondary Flows ◽  
Radius Of Curvature ◽  
Symmetric Flow ◽  
Flow Measurements ◽  
Curved Ducts ◽  
Flow Velocities ◽  
Pressure Driven

Secondary flows were experimentally examined in three 90° curved ducts with square cross sections and different radii of curvature. Dean numbers were from 1.5 × 104 to 3.6 × 104 and radius ratios of 0.5, 2.3, and 3.0 were used. Streak photography flow measurements were made and general developing secondary flow patterns were studied for three cross sections in each bend: the inlet (0° plane), the midpoint (45° plane), and the outlet (90° plane). At the 0° plane, stress driven secondary flows were found to consist of flow toward the duct corners from the center, balanced by return flow at the side bisectors. This resulted in eight symmetric flow patterns at the inlet. After a rapid transition region, the pressure driven secondary flow patterns were found to be characterized by flow moving toward the outer curved wall at the axial midplane and returning to the inner wall along the duct walls. At the 45° and 90° planes two symmetric flow patterns were observed. Secondary flow velocities in the test elbow with the smallest radius of curvature, where centrifugal forces are greater, were as much as 27% higher than secondary flows in the more gradual turns examined in this study. Also, the pressure driven secondary flows at the exit were higher than the stress driven flows at the inlet by as much as 39%. The elbow with a radius ratio of 0.5 was found to influence the upstream inlet conditions the most and the secondary flow velocities at the inlet were as much as 56% higher than for the larger radii of curvature.

Endwall Effusion Cooling System Behaviour Within a High-Pressure Turbine Cascade: Part 1—Aerodynamic Measurements

2010 ◽  
Author(s):  
Marco Sacchi ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Stefano Zecchi
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Secondary Flow ◽  
Measurement Techniques ◽  
Secondary Flows ◽  
Turbine Cascade ◽  
High Pressure Turbine ◽  
Tangential Plane ◽  
Cooling Effects ◽  
Secondary Flow Field

The secondary flow field in a large-scale high-pressure turbine cascade with micro-holed endwall cooling has been investigated at the Genova Laboratory of Aerodynamics and Turbomachinery in cooperation with Avio S.p.A in the framework of the European Project AITEB-2. The experimental investigation has been performed for the baseline configuration, with a smooth solid endwall installed, and for the cooled configuration with a micro-holed endwall providing micro-jets ejection from the wall. Two different cooling flow rates were investigated and the experimental results are reported in the paper. Different measurement techniques have been employed to analyze the secondary flow field along the channel and in a downstream tangential plane. Particle Image Velocimetry has been utilized to quantify the blade-to-blade velocity components in a plane located close to the endwall and in the midspan plane. Hot-wire measurements have been performed in a tangential plane downstream of the blade trailing edges in order to survey the micro-jets effects on the secondary flows behavior. The total pressure distributions, for the different blowing conditions, have been measured in the downstream tangential plane by means of a Kiel pneumatic probe. The results, represented in color plots of velocity, pressure loss coefficient and turbulent kinetic energy distributions, allow the identification of the endwall effusion cooling effects on location and strength of the secondary vortical structures. The thermal investigation of the effusion system is discussed in Part 2 of the paper.

Incidence Angle and Pitch–Chord Effects on Secondary Flows Downstream of a Turbine Cascade

1993 ◽  
Vol 115 (3) ◽  
pp. 383-391 ◽  
Author(s):  
A. Perdichizzi ◽  
V. Dossena
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Oil Flow ◽  
Secondary Velocity ◽  
Secondary Flow Field

This paper describes the results of an experimental investigation of the three-dimensional flow downstream of a linear turbine cascade at off-design conditions. The tests have been carried out for five incidence angles from −60 to +35 deg, and for three pitch-chord ratios: s/c = 0.58, 0.73, 0.87. Data include blade pressure distributions, oil flow visualizations, and pressure probe measurements. The secondary flow field has been obtained by traversing a miniature five-hole probe in a plane located at 50 percent of an axial chord downstream of the trailing edge. The distributions of local energy loss coefficients, together with vorticity and secondary velocity plots, show in detail how much the secondary flow field is modified both by incidence and by cascade solidity variations. The level of secondary vorticity and the intensity of the crossflow at the endwall have been found to be strictly related to the blade loading occurring in the blade entrance region. Heavy changes occur in the spanwise distributions of the pitch-averaged loss and of the deviation angle, when incidence or pitch–chord ratio is varied.

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.

Influence of Unsteady Wakes on the Secondary Flows in the Linear T106 Turbine Cascade

2016 ◽  
Author(s):  
Ilker Kirik ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Secondary Flow ◽  
High Speed ◽  
Base Flow ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Hot Wire ◽  
Flow Angle ◽  
Secondary Flow Field

The present work extends previous investigations on the secondary flows around a steady and unsteady base flow to detailed time-averaged and time-resolved flow field measurements up- and downstream of the cascade. As a representative of modern low pressure turbine rotors of moderate aerodynamic loading, the LPT cascade T106 with parallel sidewalls was chosen for these investigations. Previous investigations have shown that the intensity of secondary flows in the endwall region within a first test set-up was fairly low due to the thin endwall boundary layer at the inlet of the cascade which impeded to study the influence of periodically incoming wakes on the temporal development of the secondary flow field. For that reason a new test-up was built providing a thicker inlet boundary. Measurements have been performed in the High-Speed Cascade Wind Tunnel of the University of the Federal Armed Forces Munich under realistic Mach and Reynolds numbers. In order to simulate real turbomachinery situtations, a wake generator is installed generating temporally representative wakes in the inlet plane of the cascade by a moving bar system. The inlet conditions were determined using a hot wire and a Pitot probe. Detailed measurements of the three-dimensional flow field were carried out downstream of the cascade with a triple hot wire probe, a conventional five hole pressure probe, and a dynamic pressure probe equipped with a single Kulite sensor. All measurements were performed with and without moving bars. Based on previous investigations, a pitch of the moving bars of 40 mm and a circumferential speed of 20 m/s was chosen as the configuration with the highest influence on the secondary flow field. It is shown that the intended increase of the inlet boundary layer was achieved by putting plates on top of each other in the inlet plane endwalls. This leads to more pronounced secondary flow parameters in the spanwise distribution of the pitchwise averaged secondary flow angle (Δβ2,sec) and the secondary losses (ζ2,sec).

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