The Role of Reynolds Number Effect and Tip Leakage in Compressor Geometry Scaling at Low Turbulent Reynolds Numbers

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Markus Diehl ◽  
Christoph Schreiber ◽  
Jürg Schiffmann
Keyword(s):  
Reynolds Number ◽  
Surface Friction ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Tip Leakage ◽  
Reynolds Number Effect ◽  
Geometric Scaling ◽  
Compressor Performance ◽  
The Impact

Abstract In compressor design, a convenient way to save time is to scale an existing geometry to required specifications, rather than developing a new design. The approach works well when scaling compressors of similar size at high Reynolds numbers but becomes more complex when applied to small-scale machines. Besides the well-understood increase in surface friction due to increased relative surface roughness, two other main problems specific to small-scale turbomachinery can be specified: (1) the Reynolds number effect, describing the non-linear dependency of surface friction on Reynolds number and (2) increased relative tip clearance resulting from manufacturing limitations. This paper investigates the role of both effects in a geometric scaling process, as used by a designer. The work is based on numerical models derived from an experimentally validated geometry. First, the effects of geometric scaling on compressor performance are assessed analytically. Second, prediction capabilities of reduced-order models from the public domain are assessed. In addition to design point assessment, often found in other publications, the models are tested at off-design. Third, the impact of tip leakage on compressor performance and its Reynolds number dependency is assessed. Here, geometries of different scale and with different tip clearances are investigated numerically. Fourth, a detailed investigation regarding tip leakage driving mechanisms is carried out and design recommendations to improve small-scale compressor performance are provided.

scholarly journals Examination of Reynolds number effect on the development of round jet flow

2021 ◽  
pp. 39-47
Author(s):  
Olanrewaju Miracle Oyewola ◽  
Adebunmi Okediji ◽  
Olusegun Olufemi Ajide ◽  
Muyiwa Samuel Adaramola
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Jet Flow ◽  
Exit Section ◽  
Ambient Fluid ◽  
Potential Core ◽  
Round Jet ◽  
Reynolds Number Effect ◽  
Downstream Distance ◽  
Low Reynolds

In this study, the Reynolds number effect on the development of round jet flow is presented. The jet is produced from a smoothly contracting round nozzle and the flow structure is controlled by varying the air blower speed in order to obtain various Reynolds numbers (Re). The flow Reynolds number considered varies between 1140 and 9117. Mean velocity measurements were taken using hot-wire probe at different axial and lateral distances (0≤x/d≤50, where x is the downstream distance and d is the nozzle diameter) for the jet flow and at for 0≤x/d≤30 in long pipe attached to the nozzle. Measurements reveal that Reynolds number dictate the potential core length such that the higher the Reynolds number, the lower the potential core which is a measure of mixing of jet and ambient fluid. It shows that further away from the jet exit section, potential core decreases as Reynolds number increases, the velocity profile has a top hat shape very close to the nozzle exit and the shape is independent of Reynolds number. It is found that potential core extends up to x/d=8 for Reynolds number of 1140 as against conventional near field 0≤x/d≤6. This may suggest effect of very low Reynolds number. However, further investigation is required to ascertain this at extremely low Reynolds numbers. It is also observed that further away from the jet exit section, the higher the downstream distance, the higher the jet half-width (R1/2). Furthermore, the flow in the pipe shows almost constant value of normalised axial centerline velocity for a longer distance and this clearly indicates that there is mass redistribution rather than entrainment of ambient fluid. Overall, the Reynolds number controls the magnitude rather than the wavelength of the oscillation

scholarly journals Combined measurement of velocity and temperature in liquid metal convection

2019 ◽  
Vol 876 ◽  
pp. 1108-1128 ◽  
Author(s):  
Till Zürner ◽  
Felix Schindler ◽  
Tobias Vogt ◽  
Sven Eckert ◽  
Jörg Schumacher
Keyword(s):  
Reynolds Number ◽  
Liquid Metal ◽  
Large Scale ◽  
Scale Up ◽  
Convection Cell ◽  
Small Scale ◽  
Convection Flow ◽  
Large Scale Circulation ◽  
Large Scale Flow ◽  
The Impact

Combined measurements of velocity components and temperature in a turbulent Rayleigh–Bénard convection flow at a low Prandtl number of $Pr=0.029$ and Rayleigh numbers of $10^{6}\leqslant Ra\leqslant 6\times 10^{7}$ are conducted in a series of experiments with durations of more than a thousand free-fall time units. Multiple crossing ultrasound beam lines and an array of thermocouples at mid-height allow for a detailed analysis and characterization of the complex three-dimensional dynamics of the single large-scale circulation roll in a cylindrical convection cell of unit aspect ratio which is filled with the liquid metal alloy GaInSn. We measure the internal temporal correlations of the complex large-scale flow and distinguish between short-term oscillations associated with a sloshing motion in the mid-plane as well as varying orientation angles of the velocity close to the top/bottom plates and the slow azimuthal drift of the mean orientation of the roll as a whole that proceeds on a time scale up to a hundred times slower. The coherent large-scale circulation drives a vigorous turbulence in the whole cell that is quantified by direct Reynolds number measurements at different locations in the cell. The velocity increment statistics in the bulk of the cell displays characteristic properties of intermittent small-scale fluid turbulence. We also show that the impact of the symmetry-breaking large-scale flow persists to small-scale velocity fluctuations thus preventing the establishment of fully isotropic turbulence in the cell centre. Reynolds number amplitudes depend sensitively on beam-line position in the cell such that different definitions have to be compared. The global momentum and heat transfer scalings with Rayleigh number are found to agree with those of direct numerical simulations and other laboratory experiments.

scholarly journals Blockage Correction and Reynolds Number Dependency of an Alpine Skier: A Comparison Between Two Closed-Section Wind Tunnels

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 19
Author(s):  
Ola Elfmark ◽  
Robert Reid ◽  
Lars Morten Bardal
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Absolute Error ◽  
Reynolds Numbers ◽  
Correction Method ◽  
Wind Tunnels ◽  
Alpine Skier ◽  
Blockage Correction ◽  
Reynolds Number Dependency ◽  
The Impact

The purpose of this study was to investigate the impact of blockage effect and Reynolds Number dependency by comparing measurements of an alpine skier in standardized positions between two wind tunnels with varying blockage ratios and speed ranges. The results indicated significant blockage effects which need to be corrected for accurate comparison between tunnels, or for generalization to performance in the field. Using an optimized blockage constant, Maskell’s blockage correction method improved the mean absolute error between the two wind tunnels from 7.7% to 2.2%. At lower Reynolds Numbers (<8 × 105, or approximately 25 m/s in this case), skier drag changed significantly with Reynolds Number, indicating the importance of testing at competition specific wind speeds. However, at Reynolds Numbers above 8 × 105, skier drag remained relatively constant for the tested positions. This may be advantageous when testing athletes from high speed sports since testing at slightly lower speeds may not only be safer, but may also allow the athlete to reliably maintain difficult positions during measurements.

Small scale turbulence and the finite Reynolds number effect

2017 ◽  
Vol 29 (2) ◽  
pp. 020715 ◽  
Author(s):  
R. A. Antonia ◽  
L. Djenidi ◽  
L. Danaila ◽  
S. L. Tang
Keyword(s):  
Reynolds Number ◽  
Small Scale ◽  
Reynolds Number Effect ◽  
Scale Turbulence

Strut Interference Effects on Pitot Tube Velocity Measurements

2007 ◽  
Author(s):  
Sandra K. S. Boetcher ◽  
Ephraim M. Sparrow
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
The Body ◽  
Pitot Tube ◽  
Velocity Measurements ◽  
Measuring Device ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
Velocity Measuring ◽  
The Impact

The possible impact of the presence of the strut portion of a Pitot tube on the efficacy of the tube as a velocity-measuring device has been evaluated by numerical simulation. At sufficiently low Reynolds numbers, there is a possibility that the precursive effects of the strut could alter the flow field adjacent to the static taps on the body of the Pitot tube and might even affect the impact pressure measured at the nose. The simulations were performed in dimensionless form with the Reynolds number being the only prescribed parameter, but the dimensions were taken from a short-shanked Pitot tube. Over the Reynolds number range from 1500 to 4000, a slight effect of the strut was identified. However, the variation due to the presence of the shank of the velocity measured by the Pitot tube operating in that range of Reynolds numbers was only 1.5%.

Hot-wire spatial resolution issues in wall-bounded turbulence

2009 ◽  
Vol 635 ◽  
pp. 103-136 ◽  
Author(s):  
N. HUTCHINS ◽  
T. B. NICKELS ◽  
I. MARUSIC ◽  
M. S. CHONG
Keyword(s):  
Reynolds Number ◽  
Boundary Layers ◽  
Spatial Resolution ◽  
Reynolds Numbers ◽  
Energy Spectra ◽  
Small Scale ◽  
Wire Length ◽  
Hot Wire ◽  
Wide Range ◽  
Near Wall

Careful reassessment of new and pre-existing data shows that recorded scatter in the hot-wire-measured near-wall peak in viscous-scaled streamwise turbulence intensity is due in large part to the simultaneous competing effects of the Reynolds number and viscous-scaled wire length l+. An empirical expression is given to account for these effects. These competing factors can explain much of the disparity in existing literature, in particular explaining how previous studies have incorrectly concluded that the inner-scaled near-wall peak is independent of the Reynolds number. We also investigate the appearance of the so-called outer peak in the broadband streamwise intensity, found by some researchers to occur within the log region of high-Reynolds-number boundary layers. We show that the ‘outer peak’ is consistent with the attenuation of small scales due to large l+. For turbulent boundary layers, in the absence of spatial resolution problems, there is no outer peak up to the Reynolds numbers investigated here (Reτ = 18830). Beyond these Reynolds numbers – and for internal geometries – the existence of such peaks remains open to debate. Fully mapped energy spectra, obtained with a range of l+, are used to demonstrate this phenomenon. We also establish the basis for a ‘maximum flow frequency’, a minimum time scale that the full experimental system must be capable of resolving, in order to ensure that the energetic scales are not attenuated. It is shown that where this criterion is not met (in this instance due to insufficient anemometer/probe response), an outer peak can be reproduced in the streamwise intensity even in the absence of spatial resolution problems. It is also shown that attenuation due to wire length can erode the region of the streamwise energy spectra in which we would normally expect to see kx−1 scaling. In doing so, we are able to rationalize much of the disparity in pre-existing literature over the kx−1 region of self-similarity. Not surprisingly, the attenuated spectra also indicate that Kolmogorov-scaled spectra are subject to substantial errors due to wire spatial resolution issues. These errors persist to wavelengths far beyond those which we might otherwise assume from simple isotropic assumptions of small-scale motions. The effects of hot-wire length-to-diameter ratio (l/d) are also briefly investigated. For the moderate wire Reynolds numbers investigated here, reducing l/d from 200 to 100 has a detrimental effect on measured turbulent fluctuations at a wide range of energetic scales, affecting both the broadband intensity and the energy spectra.

scholarly journals Reynolds number trend of hierarchies and scale interactions in turbulent boundary layers

2017 ◽  
Vol 375 (2089) ◽  
pp. 20160077 ◽  
Author(s):  
W. J. Baars ◽  
N. Hutchins ◽  
I. Marusic
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Wall Turbulence ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Scale Interaction ◽  
High Reynolds ◽  
Near Wall

Small-scale velocity fluctuations in turbulent boundary layers are often coupled with the larger-scale motions. Studying the nature and extent of this scale interaction allows for a statistically representative description of the small scales over a time scale of the larger, coherent scales. In this study, we consider temporal data from hot-wire anemometry at Reynolds numbers ranging from Re τ ≈2800 to 22 800, in order to reveal how the scale interaction varies with Reynolds number. Large-scale conditional views of the representative amplitude and frequency of the small-scale turbulence, relative to the large-scale features, complement the existing consensus on large-scale modulation of the small-scale dynamics in the near-wall region. Modulation is a type of scale interaction, where the amplitude of the small-scale fluctuations is continuously proportional to the near-wall footprint of the large-scale velocity fluctuations. Aside from this amplitude modulation phenomenon, we reveal the influence of the large-scale motions on the characteristic frequency of the small scales, known as frequency modulation. From the wall-normal trends in the conditional averages of the small-scale properties, it is revealed how the near-wall modulation transitions to an intermittent-type scale arrangement in the log-region. On average, the amplitude of the small-scale velocity fluctuations only deviates from its mean value in a confined temporal domain, the duration of which is fixed in terms of the local Taylor time scale. These concentrated temporal regions are centred on the internal shear layers of the large-scale uniform momentum zones, which exhibit regions of positive and negative streamwise velocity fluctuations. With an increasing scale separation at high Reynolds numbers, this interaction pattern encompasses the features found in studies on internal shear layers and concentrated vorticity fluctuations in high-Reynolds-number wall turbulence. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’.

scholarly journals Influence of speed distribution in a rounded flow on the character of slopes erosion

2019 ◽  
Vol 20 (1) ◽  
pp. 85-95
Author(s):  
O. Ya. Maslikova ◽  
I. I. Gritsuk ◽  
D. N. Ionov ◽  
V. K. Debolskiy
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Hydraulic Structures ◽  
Natural Conditions ◽  
Channel Processes ◽  
Speed Distribution ◽  
Straight Line ◽  
River Hydraulics ◽  
Critical Reynolds Numbers ◽  
The Impact

One of the most important issues of river hydraulics is the movement of water and the formation of a channel in a stream that has a non-straight-line outline in the plan. Under natural conditions for rivers characteristic winding shape in the plan. The curvature of the jet occurs when the flow is divided into sleeves, at the inflow into the river, the confluence of flows, etc. Therefore, the study of channel processes in rivers is impossible without knowledge of the flow patterns at the curve of the channel. When designing hydraulic structures, including bridge crossings on the meandering sections of rivers, one should know the features of the dynamics of the channel in the sections of the flow turning. In winter, such areas may be narrowed due to the freezing of the channel, and during the period of ice thawing they are clogged with ice fragments. The narrowing of the canal causes an increase in the Reynolds number and a redistribution of velocity diagrams in the area under consideration, which causes a change in the erosion pattern. In laboratory conditions, the nature of the distribution of velocities and the formation of vortices on the installation, creating a rounded flow. It is shown that, at critical Reynolds numbers, a vortex countercurrent occurs in the rounded flow at the inner shore. The impact of this velocity distribution on the erosion pattern of the various slopes of the rounded flow was analyzed.

scholarly journals PENGEMBANGAN UNIT PENANGKAR BIBIT LADA BERKUALITAS DI POLITEKNIK NEGERI LAMPUNG

J-Dinamika ◽  
2018 ◽  
Vol 3 (2) ◽  
Author(s):  
Bambang Utoyo ◽  
Adryade Reshi Gusta ◽  
Yan Sukmawan ◽  
Made Same
Keyword(s):  
Large Scale ◽  
College Campus ◽  
Small Scale ◽  
Competency Development ◽  
Campus Environment ◽  
Business Units ◽  
The Impact ◽  
Training Service ◽  
And Training

Pepper is one of the spice crops that contribute to improving the Indonesian economy. Pepper cultivation is carried out on a small scale to a large scale. Pepper propagation by cutting is considered quite effective and efficient. Politeknik Negeri Lampung has been develop the Pepper Nursery Unit since 2007. This unit runs a business in the production of climbing pepper seedling, shrub pepper seedling, and pepper nursery training. The aim of this program is to support the mission of Politeknik Negeri Lampung in preparing itself to face college campus autonomy through the acquisition of revenue from established business units, accelerating the process of developing an entrepreneurial cultural system in the campus environment, providing competency development opportunities for staff and students, and increasing the role of the Politeknik Negeri Lampung for the community, especially in agriculture. The impact of this program is the availability of hight quality pepper seedling, increasing income generating Politeknik Negeri Lampung, establishment of the Pepper Nursery Unit and training service, improving the skills of Politeknik Negeri Lampung students in pepper nursery, developing entrepreneurial potential for students and staff, as well as increasing the role of Lampung State Polytechnic in community service activities.Keywords—Campus entrepreuneurship, estate crop, nursery business.

scholarly journals Technology-Driven Solutions to Prompt Conversation, Aid Communication and Support Interaction for People With Dementia and Their Caregivers: A Systematic Literature Review

2020 ◽  
Author(s):  
Viktoria Hoel ◽  
Carine Mendom Feunou ◽  
Karin Wolf-Ostermann
Keyword(s):  
Literature Review ◽  
Social Interactions ◽  
Third Party ◽  
Small Scale ◽  
People With Dementia ◽  
Conversation Partner ◽  
Person With Dementia ◽  
The Impact ◽  
The Relationship

Abstract Background The impact of dementia on communication capabilities can result in difficulties in social interactions and between people with dementia and their conversation partner, as initiating and maintaining conversations becomes increasingly challenging. The role of technology in promoting social health and participation for people with dementia is increasing, but the usage on technological devices as a third party in social interactions to enhance communication quality is still in its infancy. The objective of this literature review is to provide a comprehensive description of technology-driven interventions for people with dementia and their conversation partners to enhance communication and facilitate positive social interactions. Methods A systematic search was conducted using PubMed, CINAHL and PsycINFO, where titles and abstracts were screened by two researchers independently. The reference lists of initially identified papers were hand-searched for further relevant studies. Quality appraisal of the included studies was assessed using the Mixed Methods Appraisal Tool.Results Twenty-six papers were included., where the most common technologies to facilitate communication and interactions were tablet-computers (n=11), social robots (n=7) and PCs (n=4). By analyzing the impacts of the device(s) on social interaction and communication, five major themes emerged: i) increased interaction; ii) better understanding of the person with dementia; iii) improved conversational quality; iv) reducing pressure on the conversation partner; and v) a conversational platform.Conclusion While the majority of the included studies are small-scale, they indicate promising findings on the potential of technology in helping dyads to interact in a way that relieves strain on the caregiver, enhances the relationship and engages people with dementia in social activities. Rigorous investigation using standard, comparable measurements is needed to demonstrate the effects of technological solutions, taking on the perspective on caregiving dyads as an entity rather than looking at outcomes for one member of the dyad in isolation.

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