Near-wall flow structures and related surface quantities in wall-bounded turbulence

2021 ◽  
Vol 33 (6) ◽  
pp. 065116
Author(s):  
Tao Chen ◽  
Tianshu Liu ◽  
Zhi-Qiang Dong ◽  
Lian-Ping Wang ◽  
Shiyi Chen
Keyword(s):  
Flow Structures ◽  
Wall Flow ◽  
Wall Bounded Turbulence ◽  
Near Wall

New Facility Setup for the Investigation of Cooling Flow, Viscous and Rotational Effects on the Interstage Seal Flow Behavior of a Gas Turbine

2018 ◽  
Author(s):  
R. Guida ◽  
D. Lengani ◽  
D. Simoni ◽  
M. Ubaldi ◽  
P. Zunino
Keyword(s):  
Secondary Flow ◽  
Flow Rate ◽  
Discharge Coefficient ◽  
Flow Path ◽  
Main Flow ◽  
Coolant Flow ◽  
Flow Structures ◽  
Cooling Flow ◽  
Wall Flow ◽  
Near Wall

A new rig has been designed and commissioned at the University of Genova to study the flow field within a turbine interstage cavity and its interaction with the main flow path. The rig is a large scale one-and-half stages, rotating test facility, opportunely designed to reproduce the main features characterizing the cavity flows developing in real low pressure modules of turbogas engines. The effects due to swirl factor and the coolant injected into the cavity to prevent the thermomechanical failure of the disks have been investigated. The rig allows the evaluation of the leakage mass flow rate and the measurement of the seal discharge coefficient in the different operating conditions, as well as the characterization of viscous, rotational and coolant related effects on the main flow path, especially in terms of secondary flow structures and vane row efficiency. Pressure signals acquired into the cavity provide a direct measure of the pressurization level of the fore and rear cavities, as well as the analysis of the effects induced by rotation and coolant flow on the pressure drop provoked by the teeth. Results clearly show that once the cooling flow rate reaches a datum threshold level an iso-pressure condition (with respect to the main flow at the vane leading edge) is established into the fore part of the cavity, and the gas ingestion from the main annulus is avoided. This “purged” condition significantly modifies the near wall flow developing across the vane. The boundary layer entering the vane row is not sucked into the cavity, and simultaneously at the vane exit plane there is poor interaction between the cavity flow and the near wall flow leaving the vane. Total pressure measurements upstream and downstream of the vane clearly highlight the modification of the secondary flow structures for the different conditions tested. Overall, results reported into the paper demonstrate the capability of the new rig to provide a direct estimation of the discharge coefficient of a realistic turbine cavity system for different coolant flow rates and swirl factors, as well as to understand the effects on the flow path near wall behavior due to cavity-main flows interaction, that should be properly accounted for during the design phases, and should be properly reproduced during cascade testing.

Interaction of coherent flow structures in adverse pressure gradient turbulent boundary layers

2019 ◽  
Vol 873 ◽  
pp. 287-321 ◽  
Author(s):  
Matthew Bross ◽  
Thomas Fuchs ◽  
Christian J. Kähler
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Flow Structures ◽  
Wall Region ◽  
Strong Impact ◽  
Wall Flow ◽  
Log Law ◽  
Near Wall

With the aim to characterize the near-wall flow structures and their interaction with large-scale motions in the log-law region, time-resolved planar and volumetric flow field measurements were performed in the near-wall and log-law region of an adverse pressure gradient turbulent boundary layer following a zero pressure gradient turbulent boundary layer at a friction Reynolds number $Re_{\unicode[STIX]{x1D70F}}=5000$. Due to the high spatial and temporal resolution of the measurements, it was possible to resolve and identify uniform-momentum zones in the region $z/\unicode[STIX]{x1D6FF}<0.15$ or $z^{+}<350$ and to relate them with well known coherent flow motions near the wall. The space–time results confirm that the turbulent superstructures have a strong impact even on the very near-wall flow motion and also their alternating appearance in time and intensity could be quantified over long time sequences. Using the time record of the velocity field, rare localized separation events appearing in the viscous sublayer were also analysed. By means of volumetric particle tracking velocimetry their three-dimensional topology and dynamics could be resolved. Based on the results, a conceptual model was deduced that explains their rare occurrence, topology and dynamics by means of a complex interaction process between low-momentum turbulent superstructures, near-wall low-speed streaks and tilted longitudinal and spanwise vortices located in the near-wall region.

Fluid Flow and Heat Transfer in Duct Fan Flows with Top-Wall Rectangular-Wing Turbulators

2008 ◽  
Vol 24 (2) ◽  
pp. N15-N19
Author(s):  
T. Y. Chen ◽  
Y. H. Chen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Bottom Wall ◽  
Flow Structures ◽  
Mean Velocity ◽  
Flow Parameters ◽  
Flow And Heat Transfer ◽  
Wall Flow ◽  
Near Wall

ABSTRACTFluid flow and heat transfer in duct fan flows with a 90° rectangular-wing turbulator, mounted on the top duct wall, were experimentally studied and compared with the bottom-wall turbulator results. Threecomponent velocities were measured to characterize the flow structures and to obtain near-wall flow parameters. Temperatures on heat transfer surfaces were measured to obtain Nusselt number distributions. Results show that the turbulator has the effect to increase the near-wall axial mean velocity, axial vorticity and turbulent kinetic energy, and, consequently, augment the heat transfer. The axial mean velocity and axial vorticity play an influential role on the heat transfer distributions for the flows across the top-wall and bottom-wall turbulators, respectively.

Identification of near-wall flow structures producing large wall transfer rates in turbulent mixed convection channel flow

2010 ◽  
Vol 39 (1) ◽  
pp. 15-24 ◽  
Author(s):  
A. Fabregat ◽  
J. Pallares ◽  
A. Vernet ◽  
I. Cuesta ◽  
J.A. Ferré ◽  
...  
Keyword(s):  
Mixed Convection ◽  
Channel Flow ◽  
Flow Structures ◽  
Transfer Rates ◽  
Wall Flow ◽  
Near Wall

scholarly journals In Vitro Study of Near-Wall Flow in a Cerebral Aneurysm Model with and without Coils

2010 ◽  
Vol 31 (8) ◽  
pp. 1521-1528 ◽  
Author(s):  
L. Goubergrits ◽  
B. Thamsen ◽  
A. Berthe ◽  
J. Poethke ◽  
U. Kertzscher ◽  
...  
Keyword(s):  
Cerebral Aneurysm ◽  
In Vitro Study ◽  
Vitro Study ◽  
Wall Flow ◽  
Aneurysm Model ◽  
Near Wall

Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions

2016 ◽  
Vol 796 ◽  
pp. 257-284 ◽  
Author(s):  
Christian J. Kähler ◽  
Sven Scharnowski ◽  
Christian Cierpka
Keyword(s):  
Turbulent Flow ◽  
Flow Separation ◽  
Flow Direction ◽  
Separated Flow ◽  
Mean Flow ◽  
Complex Flow ◽  
Flow Measurements ◽  
Flow Features ◽  
Wall Flow ◽  
Near Wall

The understanding and accurate prediction of turbulent flow separation on smooth surfaces is still a challenging task because the separation and the reattachment locations are not fixed in space and time. Consequently, reliable experimental data are essential for the validation of numerical flow simulations and the characterization and analysis of the complex flow physics. However, the uncertainty of the existing near-wall flow measurements make a precise analysis of the near-wall flow features, such as separation/reattachment locations and other predicted near-wall flow features which are under debate, often impossible. Therefore, the periodic hill experiment at TU Munich (ERCOFTAC test case 81) was repeated using high resolution particle image velocimetry and particle tracking velocimetry. The results confirm the strong effect of the spatial resolution on the near-wall flow statistics. Furthermore, it is shown that statistically stable values of the turbulent flow variables can only be obtained for averaging times which are challenging to realize with highly resolved large eddy simulation and direct numerical simulation techniques. Additionally, the analysis implies that regions of correlated velocity fluctuations with rather uniform streamwise momentum exist in the flow. Their size in the mean flow direction can be larger than the hill spacing. The possible impact of the correlated turbulent motion on the wake region is discussed, as this interaction might be important for the understanding and control of the flow separation dynamics on smooth bodies.

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