Is There a Best Fixed-Geometry Valve for Micropumps?

2004 ◽  
Author(s):  
Adrian R. Gamboa ◽  
Fred K. Forster
Keyword(s):  
Reynolds Number ◽  
Weighting Function ◽  
Reverse Flow ◽  
Flow Direction ◽  
Local Maximum ◽  
Optimal Shape ◽  
Pump Design ◽  
Number Range ◽  
Optimal Shapes ◽  
Reference Shape

Two frequently used geometries for fixed-valve micropumps are the nozzle-diffuser and Tesla-type valve. However, little work has been done to investigate the relative merits of optimal shapes for each type of valve. In this study 2D steady-state computational fluid dynamics coupled with a formal optimization procedure and experimental evaluation were performed to address this problem. Non-dimensionalization of the problem allowed a comparison of the two valve types independent of physical size, i.e. shape alone was studied. Optimal shapes were found based on maximizing calculated diodicity as a function of Reynolds number in conjunction with a weighting function used to control forward pressure drop. The optimal shape for each valve was then compared numerically and experimentally to reference valves similar to those reported in the literature. The optimal shape for each valve type was found to be significantly different from the reference shape and exhibited significantly improved performance. Both valve types achieved a maximum diodicity of approximately two in the range of Reynolds number 0 ≤ Re ≤ 2000. The optimal Tesla-type valve was characterized by a large return loop and shallow return loop angle. The optimal nozzle-diffuser was characterized by a very long diffuser section that prevented flow separation in the forward flow direction along with increased wall shear stress in the reverse flow direction. The diodicity vs Reynolds number curve for the Tesla-type valve monotonically increased, while the nozzle-diffuser exhibited a local maximum in the mid-Reynolds number range. These characteristics may play an important role when valve size is determined to maximize resonant behavior of a micropump. Thus they influence numerous pump design criteria such as target flow rate-pressure characteristics and overall pump size.

Investigation of the separation bubble formed behind the sharp leading edge of a flat plate at incidence

2000 ◽  
Vol 214 (3) ◽  
pp. 157-176 ◽  
Author(s):  
M J Crompton ◽  
R V Barrett
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Laser Doppler Anemometry ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Flow Direction ◽  
Leading Edge ◽  
Laser Doppler ◽  
Static Pressure Distribution ◽  
Sharp Leading Edge

Detailed measurements of the separation bubble formed behind the sharp leading edge of a flat plate at low speeds and incidence are reported. The Reynolds number based on chord length ranged from 0.1 × 105 to 5.5 × 105. Extensive use of laser Doppler anemometry allowed detailed velocity measurements throughout the bubble. The particular advantages of laser Doppler anemometry in this application were its ability to define flow direction without ambiguity and its non-intrusiveness. It allowed the mean reattachment point to be accurately determined. The static pressure distribution along the plate was also measured. The length of the separation bubble was primarily determined by the plate incidence, although small variations occurred with Reynolds number because of its influence on the rate of entrainment and growth of the shear layer. Above about 105, the Reynolds number effect was no longer evident. The reverse flow boundary layer in the bubble exhibited signs of periodic stabilization before separating close to the leading edge, forming a small secondary bubble rotating in the opposite sense to the main bubble.

Shear-Layer Flow Regimes and Wave Instabilities and Reattachment Lengths Downstream of an Abrupt Circular Channel Expansion

1972 ◽  
Vol 39 (3) ◽  
pp. 677-681 ◽  
Author(s):  
L. H. Back ◽  
E. J. Roschke
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Reverse Flow ◽  
Flow Region ◽  
Flow Regimes ◽  
Circular Channel ◽  
Number Range ◽  
Channel Expansion ◽  
Wave Instabilities ◽  
Layer Flow

An experimental investigation of water flow through an abrupt circular-channel expansion is described over a Reynolds number range between 20 and 4200. The shear layer between the central jet and the reverse flow region along the wall downstream behaved differently in the various flow regimes that were observed. With increasing Reynolds number these regimes changed progressively from a laminar flow to an unstable vortex sheetlike flow and then to a more random fluctuating flow. The distance between the step and the reattachment location downstream correspondingly increased, reached a maximum, and then decreased. Of particular significance are the shear layer wave instabilities observed in the shear flow and their relationship to rettachment which apparently has not received much attention previously. Visual observations aided in understanding the results.

Experimental Characterization of the Separate Flow Induced by a Wall-Mounted Bump

2014 ◽  
Author(s):  
Fawzi Fadla ◽  
Laurent Keirsbulck ◽  
Fethi Aloui ◽  
J-P. Laval
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Experimental Approach ◽  
Structural Information ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Dynamical Behavior ◽  
Separate Flow ◽  
Number Range ◽  
Moderate Reynolds Number

The dynamical behavior of the flow separation induced by a wall-mounted two-dimensional bump is studied. The present investigation is based on an experimental approach that aims to provide further insight into the separate flow dynamic in such configuration. The main interest is devoted to the separation Reynolds number dependency. A general feature of separated flows dynamics is also addressed by statistical and structural information derived from the present experimental approach. Results are presented for turbulent water inflow for a moderate Reynolds-number range from 165 to 605 based on friction velocity and channel half-height (so-called Kármań number). The ratio of the bump height h and the channel full height H is 0.335. The unsteady separation process and the associate instability mechanism are very sensitive to small perturbations. So, in order to preserve the flow physics, all of the experimental techniques employed in the present study are non-intrusive. An examination of the high resolved velocity fields showed that for a moderate Kármań number, a separate area exists. Under this condition, a thin region of reverse flow was formed above the bump and a large-scale vortical activity, characterized by low-frequencies, are clearly observed. The reported results do not only yield the expected turbulent separation bubble dependencies. They also show that the well known coexisting instabilities process, which find their origin in laminar flow regime, persist for higher Kármań numbers.

scholarly journals Simulation of Flexible Fibre Particle Interaction with a Single Cylinder

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 191
Author(s):  
Naser Hamedi ◽  
Lars-Göran Westerberg
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Fibre Orientation ◽  
Flow Direction ◽  
Particle Interaction ◽  
Orientation Angle ◽  
Factors Affecting ◽  
Single Cylinder ◽  
Flow Past ◽  
Fibre Suspension

In the present study, the flow of a fibre suspension in a channel containing a cylinder was numerically studied for a very low Reynolds number. Further, the model was validated against previous studies by observing the flexible fibres in the shear flow. The model was employed to simulate the rigid, semi-flexible, and fully flexible fibre particle in the flow past a single cylinder. Two different fibre lengths with various flexibilities were applied in the simulations, while the initial orientation angle to the flow direction was changed between 45° ≤ θ ≤ 75°. It was shown that the influence of the fibre orientation was more significant for the larger orientation angle. The results highlighted the influence of several factors affecting the fibre particle in the flow past the cylinder.

scholarly journals Movement of a finite body in channel flow

2016 ◽  
Vol 472 (2191) ◽  
pp. 20160164 ◽  
Author(s):  
Frank T. Smith ◽  
Edward R. Johnson
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Flow Instability ◽  
Flow Direction ◽  
Finite Size ◽  
The Body ◽  
Thin Body ◽  
Shear Stresses ◽  
Unsteady Interaction ◽  
High Reynolds

A body of finite size is moving freely inside, and interacting with, a channel flow. The description of this unsteady interaction for a comparatively dense thin body moving slowly relative to flow at medium-to-high Reynolds number shows that an inviscid core problem with vorticity determines much, but not all, of the dominant response. It is found that the lift induced on a body of length comparable to the channel width leads to differences in flow direction upstream and downstream on the body scale which are smoothed out axially over a longer viscous length scale; the latter directly affects the change in flow directions. The change is such that in any symmetric incident flow the ratio of slopes is found to be cos ⁡ ( π / 7 ) , i.e. approximately 0.900969, independently of Reynolds number, wall shear stresses and velocity profile. The two axial scales determine the evolution of the body and the flow, always yielding instability. This unusual evolution and linear or nonlinear instability mechanism arise outside the conventional range of flow instability and are influenced substantially by the lateral positioning, length and axial velocity of the body.

Compactness of 𝑀-uniform domains and optimal thermal insulation problems

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Hengrong Du ◽  
Qinfeng Li ◽  
Changyou Wang
Keyword(s):  
Thermal Insulation ◽  
Heat Insulation ◽  
Optimization Problems ◽  
Optimal Shape ◽  
Optimal Heat ◽  
Optimal Shapes ◽  
Stable Solutions ◽  
Uniform Domains

Abstract In this paper, we will consider an optimal shape problem of heat insulation introduced by [D. Bucur, G. Buttazzo and C. Nitsch, Two optimization problems in thermal insulation, Notices Amer. Math. Soc. 64 (2017), 8, 830–835]. We will establish the existence of optimal shapes in the class of 𝑀-uniform domains. We will also show that balls are stable solutions of the optimal heat insulation problem.

Pressure Drop Measurements for Air Flow Through Open-Cell Aluminum Foam

2004 ◽  
Author(s):  
Nihad Dukhan ◽  
Angel Alvarez
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Flow Rate ◽  
Aluminum Foam ◽  
Flow Direction ◽  
The Other ◽  
Turbulent Regime ◽  
Thick Sample ◽  
Open Cell ◽  
Two Samples

Wind-tunnel pressure drop measurements for airflow through two samples of forty-pore-per-inch commercially available open-cell aluminum foam were undertaken. Each sample’s cross-sectional area perpendicular to the flow direction measured 10.16 cm by 24.13 cm. The thickness in the flow direction was 10.16 cm for one sample and 5.08 cm for the other. The flow rate ranged from 0.016 to 0.101 m3/s for the thick sample and from 0.025 to 0.134 m3/s for the other. The data were all in the fully turbulent regime. The pressure drop for both samples increased with increasing flow rate and followed a quadratic behavior. The permeability and the inertia coefficient showed some scatter with average values of 4.6 × 10−8 m2 and 2.9 × 10−8 m2, and 0.086 and 0.066 for the thick and the thin samples, respectively. The friction factor decayed with the Reynolds number and was weakly dependent on the Reynolds number for Reynolds number greater than 35.

Vortex shedding from a circular cylinder in moderate-Reynolds-number shear flow

1980 ◽  
Vol 101 (4) ◽  
pp. 721-735 ◽  
Author(s):  
Masaru Kiya ◽  
Hisataka Tamura ◽  
Mikio Arie
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Transverse Velocity ◽  
Number Range ◽  
Uniform Shear ◽  
Reynolds Number Range ◽  
Moderate Reynolds Number ◽  
Shear Parameter

The frequency of vortex shedding from a circular cylinder in a uniform shear flow and the flow patterns around it were experimentally investigated. The Reynolds number Re, which was defined in terms of the cylinder diameter and the approaching velocity at its centre, ranged from 35 to 1500. The shear parameter, which is the transverse velocity gradient of the shear flow non-dimensionalized by the above two quantities, was varied from 0 to 0·25. The critical Reynolds number beyond which vortex shedding from the cylinder occurred was found to be higher than that for a uniform stream and increased approximately linearly with increasing shear parameter when it was larger than about 0·06. In the Reynolds-number range 43 < Re < 220, the vortex shedding disappeared for sufficiently large shear parameters. Moreover, in the Reynolds-number range 100 < Re < 1000, the Strouhal number increased as the shear parameter increased beyond about 0·1.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

Aero-optics of subsonic turbulent boundary layers

2012 ◽  
Vol 696 ◽  
pp. 122-151 ◽  
Author(s):  
Kan Wang ◽  
Meng Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Dominant Role ◽  
Elevation Angle ◽  
Turbulent Boundary Layers ◽  
Density Field ◽  
Small Scale ◽  
Number Range ◽  
Scale Turbulence

AbstractCompressible large-eddy simulations are carried out to study the aero-optical distortions caused by Mach 0.5 flat-plate turbulent boundary layers at Reynolds numbers of ${\mathit{Re}}_{\theta } = 875$, 1770 and 3550, based on momentum thickness. The fluctuations of refractive index are calculated from the density field, and wavefront distortions of an optical beam traversing the boundary layer are computed based on geometric optics. The effects of aperture size, small-scale turbulence, different flow regions and beam elevation angle are examined and the underlying flow physics is analysed. It is found that the level of optical distortion decreases with increasing Reynolds number within the Reynolds-number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role, followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analysed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton’s linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.

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