Flow Development in a Circular Duct With a Highly Distorted Inlet Condition

2007 ◽  
Author(s):  
Srinivas Badam ◽  
Jie Cui ◽  
Stephen Idem
Keyword(s):  
Numerical Model ◽  
Velocity Profile ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Pressure Gradients ◽  
Development Length ◽  
Circular Duct ◽  
Inlet Velocity ◽  
Inlet Condition ◽  
Flow Development

The development of air flow downstream of a stationary fan located in a circular duct was investigated. The objective of the research was to study the evolution of the velocity profiles and pressure gradients at various axial locations. The velocity profiles were measured at three different Reynolds numbers using a five-hole directional probe. Because the stationary fan caused the inlet velocity profile to be highly distorted, it was determined experimentally that the development length exceeded 20 duct diameters. Since this was greater than the length of the apparatus, a corresponding numerical model of the flow was generated using the commercial CFD software Fluent-6.1/6.2. The numerical model was validated against the experimental results. The hydrodynamic development length was therein determined numerically.

The Effects of Fins on the Intermediate Wake of a Submarine Model

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Juan M. Jiménez ◽  
Ryan T. Reynolds ◽  
Alexander J. Smits
Keyword(s):  
Shear Stress ◽  
Velocity Profile ◽  
Outer Region ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Turbulent Wake ◽  
Self Similar ◽  
Stress Profiles

Results are presented on the behavior of the turbulent wake behind a submarine model for a range of Reynolds numbers based on the model length between 0.49×106 and 1.8×106, for test locations between 3 and 9 diameters downstream of the stern. The shape of the model emulates an idealized submarine, and tests were performed with and without stern fins. In the absence of fins, the velocity profile in planes away from the influence of the sail rapidly becomes self-similar and is well described by a function of exponentials. The fins create defects in the velocity profiles in the outer region of the wake, while yielding higher values of turbulence at locations corresponding to the tips of the fins. Measurements conducted in planes away from the midline plane show that the velocity profiles remain self-similar, while the shear stress profiles clearly show the effects of the necklace vortices trailing from the base of the fins.

Numerical Optimization of the Inlet Velocity Profile Ingested by the Conical Draft Tube of a Hydraulic Turbine

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Sergio Galván ◽  
Marcelo Reggio ◽  
Francois Guibault
Keyword(s):  
Velocity Profile ◽  
Flow Rate ◽  
Numerical Optimization ◽  
Draft Tube ◽  
Velocity Profiles ◽  
Plant Performance ◽  
Swirl Number ◽  
Inlet Velocity ◽  
Turbine Performance ◽  
Low Head

Past numerical and experimental research has shown that the draft tube inlet velocity is critically important to hydropower plant performance, especially in the case of low-head installations. However, less is known about the influence of flow parameters on turbine performance particularly swirl distribution. Based on the influence of draft tube flow characteristics on the overall performance of a low-head turbine, this research proposes a methodology for optimizing draft tube inlet velocity profiles as a new approach to controlling the flow conditions in order to yield better draft tube and turbine performance. Numerical optimization methods have been used successfully for a variety of design problems. However, addressing the optimization of boundary conditions in hydraulic turbines poses a new challenge. In this paper, three different vortex equations for representing the inlet velocity profile are applied to a cone diffuser, and the behavior of the objective function is analyzed. As well, the influence of the quantitative correlation between the swirling flow at the cone inlet and the analytical blade shape, flow rate, and swirl number using the best inlet velocity profiles is evaluated. We also include a discussion on the development of a flow structure caused by the inlet swirl parameters. Finally, we present an analysis of the influence of flow rate and swirl number on the behavior of the optimization process.

Velocity Measurements of Shear Flows by a Novel Velocity Profile Sensor With Micrometer Spatial Resolution

2003 ◽  
Author(s):  
Ju¨rgen Czarske ◽  
Lars Bu¨ttner ◽  
Thorsten Razik ◽  
Harald Mu¨ller ◽  
Dietrich Dopheide ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Boundary Layers ◽  
Spatial Resolution ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Precise Determination ◽  
Measuring System ◽  
Laser Doppler Velocimeter ◽  
Tracer Particles

A measuring system based on a differential laser-Doppler velocimeter has been extended to determine one-dimensional velocity profiles with a spatial resolution inside the measurement volume. The principle of the velocity profile sensor is based on the generation of two fringe systems with different gradients of the fringe spacings. The determination of the corresponding two Doppler frequencies yields the position as well as the velocity component of individual tracer particles, which results in the velocity profile for detecting several particles. The sensor was used to determine velocity profiles of flat-plate laminar boundary layers for varying Reynolds numbers. A precise determination of the wall shear stress was accomplished. All results are in good agreement with the theory. The main application of the velocity profile sensor is the spatial high-resolved investigation of turbulent boundary layers.

Computational Study of the Effect of Inlet Velocity Profile and Rib Orientation on Heat Transfer in Rotating Ribbed Radial Turbine Cooling Passages

2016 ◽  
Author(s):  
Robert Pearce ◽  
Peter Ireland ◽  
Matthew McGilvray ◽  
Eduardo Romero
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Velocity Profile ◽  
Computational Study ◽  
Velocity Profiles ◽  
Turbine Engine ◽  
Inlet Velocity ◽  
Turbine Cooling ◽  
Radial Turbine

This study investigates the effect of inlet velocity profiles and rib orientations on the Nusselt number distribution within ribbed radial turbine cooling passages representative of systems used in current engines. A triple-pass serpentine passage is investigated, which includes rib turbulators angled at 45° and 180° bends. The first two passes are radially outward and inward respectively and both have an aspect ratio of 1:4, with the third pass radially outward with an aspect ratio of 1:2. Multiple inlet velocity profiles are studied in RANS CFD simulations under both stationary and rotating conditions. The rotating simulations have Reynolds, Rotation and Buoyancy numbers representative of a passage within a HP turbine blade of a gas turbine engine. The flow structure and Nusselt number distributions are discussed in detail with the inlet velocity profile found to have a very large influence in the first pass under both stationary and rotating conditions, with smaller differences observed in the later passes. The rib orientation in the second pass was also investigated, with simulations of reversed and non-reversed rib orientation compared. Improved heat transfer characteristics were found in simulations where the ribs were orientated in the same direction for all three passages. These simulations are compared to experimental results in order to explain previous discrepancies found between experimental and CFD data from an experimental setup with complex inlet geometry.

scholarly journals Effect of Inlet Velocity Profiles on Patient-Specific Computational Fluid Dynamics Simulations of the Carotid Bifurcation

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Ian C. Campbell ◽  
Jared Ries ◽  
Saurabh S. Dhawan ◽  
Arshed A. Quyyumi ◽  
W. Robert Taylor ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Velocity Profile ◽  
Carotid Bifurcation ◽  
Velocity Profiles ◽  
Patient Specific ◽  
Flow Waveform ◽  
Specific Flow ◽  
Inlet Velocity ◽  
The Mean

Patient-specific computational fluid dynamics (CFD) is a powerful tool for researching the role of blood flow in disease processes. Modern clinical imaging technology such as MRI and CT can provide high resolution information about vessel geometry, but in many situations, patient-specific inlet velocity information is not available. In these situations, a simplified velocity profile must be selected. We studied how idealized inlet velocity profiles (blunt, parabolic, and Womersley flow) affect patient-specific CFD results when compared to simulations employing a “reference standard” of the patient’s own measured velocity profile in the carotid bifurcation. To place the magnitude of these effects in context, we also investigated the effect of geometry and the use of subject-specific flow waveform on the CFD results. We quantified these differences by examining the pointwise percent error of the mean wall shear stress (WSS) and the oscillatory shear index (OSI) and by computing the intra-class correlation coefficient (ICC) between axial profiles of the mean WSS and OSI in the internal carotid artery bulb. The parabolic inlet velocity profile produced the most similar mean WSS and OSI to simulations employing the real patient-specific inlet velocity profile. However, anatomic variation in vessel geometry and the use of a nonpatient-specific flow waveform both affected the WSS and OSI results more than did the choice of inlet velocity profile. Although careful selection of boundary conditions is essential for all CFD analysis, accurate patient-specific geometry reconstruction and measurement of vessel flow rate waveform are more important than the choice of velocity profile. A parabolic velocity profile provided results most similar to the patient-specific velocity profile.

An Initial Approach to the Design of Very Wide Angle Axisymmetric Diffusers With Gauzes to Achieve Uniform Outlet Velocity Profiles

1977 ◽  
Vol 99 (2) ◽  
pp. 357-364 ◽  
Author(s):  
N. L. Kachhara ◽  
J. L. Livesey ◽  
P. L. Wilcox
Keyword(s):  
Velocity Profile ◽  
Major Part ◽  
Pressure Rise ◽  
Velocity Profiles ◽  
Moderate Pressure ◽  
Wide Angle ◽  
Pressure Gradients ◽  
Optimum Location ◽  
Comparable Performance ◽  
Sudden Enlargement

A method is presented of designing very wide angle axisymmetric diffusing ducts which achieve uniform outlet velocity profiles. The aim was to concentrate the major part of the diffuser pressure rise on a small portion of the duct boundary with zero or favorable pressure gradients on the remainder of the boundary. With an optimum location and design of gauze the diffusers are capable of giving a very uniform outlet velocity profile in a short overall length, when working with thin inlet boundary layers and some, although recognizably moderate, pressure recovery. One diffuser tested (diffuser C) produced uniform outlet velocity profiles in approximately 1.5 inlet diameters compared with the 10 diameters required for a sudden enlargement having comparable performance.

Large Eddy Simulation of Forced and Unforced Plane Jets Impinging on a Convex Surface

2014 ◽  
Author(s):  
N. Kharoua ◽  
L. Khezzar ◽  
Z. Nemouchi ◽  
M. AlShehhi
Keyword(s):  
Large Eddy Simulation ◽  
Velocity Profile ◽  
Axial Velocity ◽  
Velocity Profiles ◽  
Impinging Jets ◽  
Inlet Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Target Wall ◽  
The Mean

Large Eddy Simulation study of plane impinging jets with different inlet velocity profiles was conducted. The inlet velocity profile was forced at a frequency equal to 600Hz and amplitude equal to 30% of the mean inlet velocity. The Reynold number, based on the jet width W and the inlet velocity, is equal to 5600. The distance of the jet exit from the target wall was varied from 2W to 10W to cover different types of impinging jets with different flow structures. The time-averaged Nusselt Number Nu profiles, along the curved wall, are characterized by two peaks for the shortest distance 2W and only one peak, at the impingement region, for the largest distance 10W. The first peak, at the impingement region is investigated through profiles of the mean axial velocity, the rms axial velocity, the mean static pressure, and the mean static temperature plotted on the jet centerline. For the second peak of the Nu (2W case), the turbulence level and the thickness of the highly turbulent layer near the curved wall were depicted on curved lines parallel and very close to the target wall. Forcing the considered jets at 600Hz was found to reduce the Nu while a fully developed inlet velocity profile causes an important increase of the Nu at the impingement region compared with flat inlet velocity profiles.

Impact of inlet velocity profile on stenotic flow development

2006 ◽  
Vol 39 ◽  
pp. S303-S304
Author(s):  
S.D. Peterson ◽  
S. Poussou ◽  
M.W. Plesniak
Keyword(s):  
Velocity Profile ◽  
Inlet Velocity ◽  
Flow Development

scholarly journals To the Question of a Logarithmic Velocity Profile Correspondence with the Experimental Data

2020 ◽  
Vol 22 (2) ◽  
pp. 637-648
Author(s):  
A. E. Zaryankin
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Velocity Profile ◽  
Scientific Literature ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Turbulence Theory ◽  
Definition Of ◽  
Semi Empirical ◽  
Logarithmic Velocity Profile

AbstractThe methodology of obtaining a logarithmic velocity profile describing the velocity distribution in the cross section of the boundary layer, which is based on the well-known equation of L. Prandtl, based on its semi-empirical turbulence theory, is considered.It is shown that the logarithmic velocity profile obtained in this way does not satisfy any boundary condition arising from the classical definition of such concept as the boundary layer.The perfect coincidence of this velocity profile with the experimental data of Nikuradze demonstrated in the world scientific literature is a consequence of making these profiles not in a fixed, but in a floating coordinate system. When rebuilding the velocity profiles obtained at different Reynolds numbers, all the profiles lose their versatility and do not coincide with the actual velocity profiles in cylindrical pipes.

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