Secondary flow vortical structures in a 180∘ elastic curved vessel with torsion under steady and pulsatile inflow conditions

2018 ◽  
Vol 3 (1) ◽  
Author(s):  
Mohammad Reza Najjari ◽  
Michael W. Plesniak
Keyword(s):  
Secondary Flow ◽  
Vortical Structures ◽  
Inflow Conditions

Experimental Study of Large-Scale Flow Structures in an Aneurysm

2018 ◽  
Author(s):  
Paulo Yu ◽  
Vibhav Durgesh
Keyword(s):  
Large Scale ◽  
Flow Structures ◽  
Pump System ◽  
Vortical Structures ◽  
Abnormal Growth ◽  
Image Velocimetry ◽  
Large Scale Flow ◽  
The Impact ◽  
Inflow Conditions ◽  
Aneurysm Model

An aneurysm is an abnormal growth in the wall of a weakened blood vessel, and can often be fatal upon rupture. Studies have shown that aneurysm shape and hemodynamics, in conjunction with other parameters, play an important role in growth and rupture. The objective of this study was to investigate the impact of varying inflow conditions on flow structures in an aneurysm. An idealized rigid sidewall aneurysm model was prepared and the Womersley number (α) and Reynolds number (Re) values were varied from 2 to 5 and 50 to 250, respectively. A ViVitro Labs pump system was used for inflow control and Particle Image Velocimetry was used for conducting velocity measurements. The results showed that the primary vortex path varied with an increase in α, while an increase in Re was correlated to the vortex strength and formation of secondary vortical structures. The evolution and decay of vortical structures were also observed to be dependent on α and Re.

Formation and interaction of multiple secondary flow vortical structures in a curved pipe: transient and oscillatory flows

2019 ◽  
Vol 876 ◽  
pp. 481-526 ◽  
Author(s):  
Mohammad Reza Najjari ◽  
Christopher Cox ◽  
Michael W. Plesniak
Keyword(s):  
Secondary Flow ◽  
Initial Conditions ◽  
Inlet Section ◽  
Vortex Identification ◽  
Navier Stokes Equation ◽  
Cross Sectional ◽  
Oscillatory Flows ◽  
Axis Orientation ◽  
Vortical Structures ◽  
Curved Pipe

Transient, steady and oscillatory flows in a $180^{\circ }$ curved pipe are investigated both numerically and experimentally to understand secondary flow vortex formation and interactions. The results of numerical simulations and particle image velocimetry experiments are highly correlated, with a low error. To enable simulations in a smaller domain with shorter inlet section, an analytical solution for the unsteady Navier–Stokes equation is obtained with non-zero initial conditions to provide physical velocity profiles for the simulations. The vorticity transport equation is studied and its terms are balanced to find the mechanism of vorticity transfer to structures in the curved pipe. Several vortices are identified via various vortex identification (ID) methods and their results are compared. Isosurfaces of the $\unicode[STIX]{x1D706}_{2}$ vortex ID are used to explain the temporal and spatial evolution of vortices in the curved pipe. Eigenvalues and eigenvectors of the velocity gradient tensor are calculated for the swirling strength vortex ID method, which also determines vortex axis orientation. The classical Lyne vortex in oscillatory flow with an inviscid core is also revisited and its results are compared with the transient and steady flows. These in-depth analyses provide a better understanding and characterization of vortical structures in the curved pipe flow. Our findings show that, although there are some visual similarities between cross-sectional views of steady/transient flows and oscillatory flows, the structure herein designated as Lyne-type vortex detected in the cross-sections (under steady, transient and pulsatile flows) is not the same as the classical Lyne vortex pair (in oscillatory flows).

Numerical Investigations on Effect of Inflow Parameters on Development of Secondary Flow Field for Linear LP Turbine Cascade

2021 ◽  
Author(s):  
Anand P. Darji ◽  
Beena D. Baloni ◽  
Chetan S. Mistry
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Turbulence Model ◽  
Turbulence Intensity ◽  
Numerical Study ◽  
Turbine Cascade ◽  
Wall Flow ◽  
End Wall ◽  
Inflow Conditions ◽  
Secondary Flow Field

Abstract End wall flows contribute the most crucial role in loss generation for axial flow turbine and compressor blades. These losses lead to modify the blade loading and overall performance in terms of stable operating range. Present study aimed to determine the end wall flow streams in a low speed low pressure linear turbine cascade vane using numerical approach. The study includes two sections. The first section includes an attempt to understand different secondary flow streams available at end wall. Location of generation of horseshoe vortex streams and subsequent vortex patterns are identified in the section. The selection of suitable turbulence model among SST (Shear Stress Transport) k–ω and SST γ–θ to identify end wall flow streams is studied in prior in the section. The steady state numerical study is performed using Reynolds Averaged Navier-Stoke’s Equations closed by SST γ–θ turbulence model. The computational results are validated with experimental results available in the literature and are found to be in good agreement. The study is extended for different inflow conditions in later section. The second section includes effect of flow incidence and turbulence intensity on the end wall secondary flow field. Inflow incidences considered for the study are −20°, −10°, 0° (design incidence), +10° and +20°. The inlet turbulence intensities are varied by 1% and 10% for each case. The results revealed different secondary flow patterns at an end wall and found the change in behavior with an inflow conditions. SST γ–θ turbulence model with lower turbulence intensity is more suitable to identify such flow behavior.

Impact of Varying High- and Low-Pressure Turbine Purge Flows on a Turbine Center Frame and Low-Pressure Turbine System

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
P. Z. Sterzinger ◽  
S. Zerobin ◽  
F. Merli ◽  
L. Wiesinger ◽  
A. Peters ◽  
...  
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Low Pressure ◽  
Flow Structures ◽  
Flow Conditions ◽  
High Pressure Turbine ◽  
Inlet Flow ◽  
Low Pressure Turbine ◽  
The Impact ◽  
Inflow Conditions

Abstract This paper presents the experimental and numerical evaluation and comparison of the different flow fields downstream of a turbine center frame duct and a low-pressure turbine (LPT) stage, generated by varying the inlet flow conditions to the turbine center frame (TCF) duct. The measurements were carried out in an engine-representative two-stage two-spool test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. The rig consists of a high-pressure turbine (HPT) and a LPT turbine stage, connected via a TCF with non-turning struts. Four individual high-pressure turbine purge flowrates and two low-pressure turbine purge flowrates were varied to achieve different engine-relevant TCF and LPT inlet flow conditions. The experimental data were acquired by means of five-hole-probe (5HP) area traverses upstream and downstream of the TCF and downstream of the LPT. A steady Reynolds-averaged Navier–Stokes (RANS) simulation taking all purge flows in account was used for comparison, and additional insights are gained from a numerical variation of the HPT and LPT purge flowrates. The focus of this study is on the impact of the variations in TCF inlet conditions on the secondary flow generation through the TCF duct and the carryover effects on the exit flow field and performance of the LPT stage. Existing work is limited by either investigating multistage LPT configurations with generally very few measurements behind the first stage or by not including relevant HPT secondary flow structures in setting up the LPT inflow conditions. This work addresses both of these shortcomings and presents new insight into the TCF and LPT aerodynamic behavior at varying the HPT and LPT purge flows. The results demonstrate the importance of the HPT flow structures and their evolution through the TCF duct for setting up the LPT inflow conditions and ultimately for assessing the performance of the first LPT stage.

Effects of Platform Misalignment in a 3D Designed 1.5 Stage Axial Turbine

2014 ◽  
Author(s):  
R. Kluxen ◽  
M. Terstegen ◽  
S. Behre ◽  
P. Jeschke ◽  
Y. Guendogdu
Keyword(s):  
Secondary Flow ◽  
Channel Height ◽  
Beneficial Effects ◽  
Blade Row ◽  
Outlet Flow ◽  
Flow Intensity ◽  
Comparison Of The Results ◽  
Yaw Angle ◽  
Near Future ◽  
Inflow Conditions

The effect of hub platform misalignment in the first vane of a 1.5 stage axial test rig turbine on the efficiency is numerically analyzed. An investigation is made into how this misalignment, as caused for example by manufacturing deviation, impacts the intended 3D flow in an endwall-contoured design and how robust the design is compared to a uncontoured turbine. Axial misalignment was created by extending all platforms within the blade row in radial direction by up to 5.5 % of the channel height. In order to create circumferential steps, only every third platform was elevated. The results are based on steady and unsteady simulations with the DLR RANS solver TRACE. In general, both axial and circumferential steps alter the static pressure field and lead to flow separations bubbles. These effects lead to the creation of new vortices which interact with the classic turbine secondary flow. It turns out that increasing the step height generally reinforces the secondary flow intensity. In addition to local detrimental effects, these processes significantly alter the inflow conditions to the subsequent blade rows, leading to increased losses there. A comparison of the results for the uncontoured and the non-axisymmetric endwall shows that the beneficial effects of the latter, which are based mainly on radial homogenization of the outlet flow yaw angle in the first vane, still continue to exist in the presence of platform steps, although the overall efficiency is significantly reduced. An experimental validation of the platform effects is not included in this paper but will follow in the near future.

DNS of the Flow Near the Endwall in a Linear Low Pressure Turbine Cascade With Periodically Passing Wakes

2014 ◽  
Author(s):  
Denis Koschichow ◽  
Jochen Fröhlich ◽  
Ilker Kirik ◽  
Reinhard Niehuis
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Direct Numerical Simulations ◽  
Experimental Setup ◽  
Turbine Cascade ◽  
Vortical Structures ◽  
Low Pressure Turbine ◽  
Turbulent Inflow ◽  
Inflow Conditions

Direct numerical simulations (DNS) were used to study the effects of periodic incoming wakes on the flow near the endwall in a linear turbine cascade T106. The moving cylindrical bars generating the wakes in the experiment were represented by means of appropriate unsteady turbulent inflow conditions. In the simulations, two cases, with and without incoming wakes, were conducted at a Reynolds number of 90,000 based on chord length and outlet velocity. The results were validated with experimental data. Due to constructive limitations of the experimental setup, the incoming boundary layer is very thin, so that some features of the secondary flow are absent or small. Employing phase-averaging, however, the periodic formation of vortical structures caused by the wakes can be identified in the vicinity of the endwall.

Impact of Varying High- and Low-Pressure Turbine Purge Flows on a Turbine Center Frame and Low-Pressure Turbine System

2019 ◽  
Author(s):  
P. Z. Sterzinger ◽  
S. Zerobin ◽  
F. Merli ◽  
L. Wiesinger ◽  
A. Peters ◽  
...  
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Low Pressure ◽  
Flow Structures ◽  
Turbine Stage ◽  
Flow Conditions ◽  
Flow Rates ◽  
Low Pressure Turbine ◽  
Purge Flow ◽  
Inflow Conditions

Abstract This paper presents the experimental and numerical evaluation and comparison of the different flow fields downstream of a turbine center frame duct and a low-pressure turbine stage, generated by varying the inlet flow conditions to the turbine center frame duct. The measurements were carried out in an engine-representative two-stage two-spool test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. The rig consists of a high-pressure (HPT) and a low-pressure (LPT) turbine stage, connected via a turbine center frame (TCF) with non-turning struts. Four individual high-pressure turbine purge flow rates and two low-pressure turbine purge flow rates were varied to achieve different engine-relevant TCF and LPT inlet flow conditions. The experimental data was acquired by means of five-hole-probe area traverses upstream and downstream of the TCF, and downstream of the LPT. A steady RANS simulation taking all purge flows in account was used for comparison and additional insight are gained from a numerical variation of the HPT and LPT purge flow rates. The focus of this study is on the impact of the variations in TCF inlet conditions on the secondary flow generation through the TCF duct and the carry-over effects on the exit flow field and performance of the LPT stage. Existing work is limited by either investigating multi-stage LPT configurations with generally very few measurements behind the first stage or by not including relevant HPT secondary flow structures in setting up the LPT inflow conditions. This work addresses both of these shortcomings and presents new insight into the TCF and LPT aerodynamic behavior at varying the HPT and LPT purge flows. The results demonstrate the importance of the HPT flow structures and their evolution through the TCF duct for setting up the LPT inflow conditions, and ultimately for assessing the performance of the first LPT stage.

Numerical Computation of the Pulsatile Flow in a Turbocharger With Realistic Inflow Conditions From an Exhaust Manifold

2009 ◽  
Author(s):  
Fredrik Hellstrom ◽  
Laszlo Fuchs
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Mass Flow ◽  
Pulsatile Flow ◽  
Exhaust Manifold ◽  
Ic Engine ◽  
Turbine Performance ◽  
Radial Turbine ◽  
Flow Components ◽  
Inflow Conditions

The combined effect of different secondary perturbations at the turbine inlet and the pulsatile flow on the turbine performance was assessed and quantified by using Large Eddy Simulation. The geometrical configuration consists of a 4-1 exhaust manifold and a radial turbine. At the inlet to each port of the manifold, engine realistic pulsatile mass flow and temperature fields are specified. The turbine used in this numerical study is a vaneless radial turbine with 9 blades, with a size that is typical for a turbocharger mounted on a 2.0 liters IC engine of passenger cars. The flow field is investigated and the generated vortices are visualized to enable a better insight into the unsteady flow field. Correlations between the turbine inflow conditions, such as mass flow rate, strength of secondary flow components, and the turbine performance have also been studied. The results show that the flow field entering the turbine is heavily disturbed with strong secondary flow components and disturbed axial velocity profile. Between the inlet to the turbine and the wheel, the strength of the secondary flow and the level of the disturbances of the axial flow decrease which gives large losses in this region. Even though the magnitude of the disturbances decrease, the flow entering the wheel will still be disturbed, resulting in a perturb inlet flow to the wheel which affects the shaft power output from the turbine.

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