Concave wall-based mixing chambers and convex wall-based constriction channel micromixers

2019 ◽  
pp. 1-23 ◽  
Author(s):  
Ranjitsinha R. Gidde
Keyword(s):  
Concave Wall ◽  
Convex Wall ◽  
Mixing Chambers

Analysis of Draw Bead Geometry on Wall Thinning and Concave/Convex Feature in Rectangular Deep Drawn Parts

2011 ◽  
Vol 189-193 ◽  
pp. 2704-2707 ◽  
Author(s):  
Wiriyakorn Phanitwong ◽  
Sutasn Thipprakmas
Keyword(s):  
Finite Element Method ◽  
Bead Geometry ◽  
Distribution Analysis ◽  
The Finite Element Method ◽  
Bead Width ◽  
Wall Thinning ◽  
Concave Wall ◽  
Straight Wall ◽  
Convex Wall ◽  
Bead Height

The application of the draw bead could reduce the concave/convex wall features. However, it also affected the wall thinning. Therefore, it is difficult to determine the suitable draw bead geometry to obtain a straight wall without the wall thinning. In this study, the effects of draw bead geometry of height and width on concave/convex wall feature and wall thinning were investigated by using the finite element method (FEM) and experiments. Based on the stress distribution analysis, the increasing in draw bead width and the decreasing in draw bead height lead to the concave wall feature increased; however, the application of the too small draw bead width and the too large draw bead height generated the convex wall feature. The wall thinning also decreased as the draw bead width increased as well as the draw bead height decreased. Therefore, the application of suitable draw bead height and width significantly suppressed the concave/convex wall feature and wall thinning, which resulted in the straight wall with the smallest wall thinning could be achieved.

Extension of the Wall-Driven Enclosure Flow Problem to Toroidally Shaped Geometries of Square Cross-Section

1996 ◽  
Vol 118 (4) ◽  
pp. 779-786 ◽  
Author(s):  
L. M. Phinney ◽  
J. A. C. Humphrey
Keyword(s):  
Cross Section ◽  
Fluid Motion ◽  
Radius Of Curvature ◽  
Two Dimensional ◽  
Coordinate Direction ◽  
Concave Wall ◽  
Center Vortex ◽  
Convex Wall ◽  
Two Dimensional Flow ◽  
Moving Fluid

The two-dimensional wall-driven flow in an enclosure has been a numerical paradigm of long-standing interest and value to the fluid mechanics community. In this paradigm the enclosure is infinitely long in the x-coordinate direction and of square cross-section (d × d) in the y-z plane. Fluid motion is induced in all y-z planes by a wall (here the top wall) sliding normal to the x-coordinate direction. This classical numerical paradigm can be extended by taking a length L of the geometry in the x-coordinate direction and joining the resulting end faces at x = 0 and x = L to form a toroid of square cross-section (d × d) and radius of curvature Rc. In the curved geometry, axisymmetric fluid motion (now in the r-z planes) is induced by sliding the top flat wall of the toroid with an imposed radial velocity, ulid, generally directed from the convex wall towards the concave wall of the toroid. Numerical calculations of this flow configuration are performed for values of the Reynolds number (Re = ulidd/ν) equal to 2400, 3200, and 4000 and for values of the curvature ratio (δ = d/Rc) ranging from 5.0 · 10−6 to 1.0. For δ ≤ 0.05 the steady two-dimensional flow pattern typical of the classical (straight) enclosure is faithfully reproduced. This consists of a large primary vortex occupying most of the enclosure and three much smaller secondary eddies located in the two lower corners and the upper upstream (convex wall) corner of the enclosure. As δ increases for a fixed value of Re, a critical value, δcr, is found above which the primary center vortex spontaneously migrates to and concentrates in the upper downstream (concave wall) corner. While the sense of rotation originally present in this vortex is preserved, that of the slower moving fluid below it and now occupying the bulk of the enclosure cross-section is reversed. The relation marking the transition between these two stable steady flow patterns is predicted to be δcr1/4 = 3.58 Re-1/5 (δ ± 0.005).

Film Cooling of a Gas Turbine Blade

1978 ◽  
Vol 100 (3) ◽  
pp. 476-481 ◽  
Author(s):  
S. Ito ◽  
R. J. Goldstein ◽  
E. R. G. Eckert
Keyword(s):  
Gas Turbine ◽  
Turbine Blade ◽  
Film Cooling ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Large Momentum ◽  
Gas Turbine Blade ◽  
Momentum Flux Ratio ◽  
Concave Wall ◽  
Convex Wall

The local film-cooling produced by a row of jets on a gas turbine blade is measured by a mass transfer technique. The density of the secondary fluid is from 0.75 to two times that of the mainflow and the range of the mass flux ratio is from 0.2 to three. The effect of blade-wall curvature on the film-cooling effectiveness is very significant. On the convex wall, a near tangential jet is pushed towards the wall by the static pressure force around the jet. For a small momentum flux ratio, this results in a higher effectiveness compared with that on a flat wall. At a large momentum flux ratio, however, the jet tends to move away from the curved wall because of the effect of inertia of the jet resulting in a smaller effectiveness on the convex wall. On the concave wall, the effects of curvature are the reverse of those described for the convex wall.

scholarly journals Experimental study on fiber suspensions in a curved expansion duct with particle image velocimetry

2012 ◽  
Vol 16 (5) ◽  
pp. 1414-1418 ◽  
Author(s):  
Xiao-Yu Liang ◽  
Huan-Huan Wu ◽  
Cheng-Xu Tu ◽  
Kai Zhang
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Flow Rate ◽  
Particle Image ◽  
Flow Direction ◽  
Internal Flow ◽  
Concave Wall ◽  
Image Velocimetry ◽  
Inlet Flow Rate ◽  
Convex Wall

The visualization measurement of internal flow field in a curved expansion duct is experimentally studied using particle image velocimetry technology and the influence of flow rate on flow field is analyzed. The streamline distribution and related performance curve in the internal flow field can be figured out through further analysis of experiment data. The results show that fiber orientation is mainly affected by velocity gradient, the fibers near the wall are aligned with the flow direction more quickly than the fibers in intermediate region, and the fibers near the concave wall are more quickly aligned with the flow direction than the convex wall. The larger inlet flow rate which will accordingly lead to increase inlet velocity enables the more quick adaptation and steady of fibers in flow direction.

Relaxation of Spatially Advancing Coherent Structures in a Turbulent Curved Channel Flow

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Koji Matsubara ◽  
Tomoya Ohishi ◽  
Keisuke Shida ◽  
Takahiro Miura
Keyword(s):  
Small Scale ◽  
Computational Domain ◽  
Mean Flow ◽  
Curved Channel ◽  
Concave Wall ◽  
Convex Wall ◽  
Mean Pressure ◽  
Coherent Vortex ◽  
The Mean ◽  
Scale Turbulence

A direct numerical simulation is made for the incompressible turbulent flow in the 180 deg curved channel with a long straight portion connected to its exit port. An examination is made for how the organized coherent vortex grows and decays in the curved channel: the radius ratio of 0.92, the aspect ratio of 7.2, and the succeeding straight section length of 75 times the channel half width. The 1552 × 91 × 128 ( = 18,427,136) grids are allocated to the computational domain. The frictional-velocity-based Reynolds number is kept at 150 to resolve the long domain including curved and straight regions. In contrast to that the coherent vortex grows along the concave wall, the vortex remains strong in the convex-wall side after the curvature accompanying a tail of the small-scale turbulence near the convex wall. The dissimilarity between the onset and disappearing of the coherent vortex essentially comes from the mean pressure gradient, which aids or averts the near-wall fluid oppositely between the curvature inlet and the exit. The mean flow is decelerated near the inlet of the convex wall to destabilize the flow and to trigger the onset of the coherent vortex. Contrary, the mean flow is accelerated near the exit of the convex wall to weaken the coherent vortex, and is decelerated near the exit of the concave wall to enhance the turbulence. Therefore, the turbulence enhancement and attenuation occurs oppositely between the inlet and exit of the curvature, and the coherent vortex draws a wake in the convex-side rather than the concave-side where it starts.

Shock diffraction in channels with 90° bends

1983 ◽  
Vol 132 ◽  
pp. 257-270 ◽  
Author(s):  
D. H. Edwards ◽  
P. Fearnley ◽  
M. A. Nettleton
Keyword(s):  
Mach Number ◽  
Rectangular Cross Section ◽  
Outer Wall ◽  
Incident Shock ◽  
Radius Of Curvature ◽  
Shock Diffraction ◽  
Expansion Waves ◽  
Concave Wall ◽  
Convex Wall ◽  
Shock Profiles

A study has been made of how initially planar shocks in air propagate around 90° bends in channels of nearly rectangular cross-section. In shallow bends for which the radius of curvature R is much greater than the radius r of the channel, the shock recovers from a highly curved profile at the start of the bend to regain planarity towards the end of the bend. This occurs on account of the acceleration of the triple point across the channel following its interaction with the expansion waves generated at the convex wall. In sharp bends the shock profiles retain their pronounced curvature for some distance downstream of the bend.At the start of a shallow bend (R/r ≈ 6) the shock at the concave wall, initial Mach number M0, accelerates to Mw = 1.15M0 and remains at this value until towards the end of the bend it begins to attenuate. At the convex wall, shocks of M0 > 1.7 attenuate to Mw = 0.7M0 and propagate at this value for some distance around the bend. In the early stages of a sharper bend (R/r ≈ 3) the shock at the concave wall strengthens to Mw = 1.3M0, remaining at this value for some distance downstream of the bend. At the convex wall the shock decelerates to 0.6M0.Whitham's (1974) ray theory is shown to predict with reasonable accuracy the Mach numbers of the wall shocks at both surfaces for both bends tested and the range of incident shock velocities used, 1.2 < M0 < 3. The agreement between the theory and experimental results is particularly close for stronger shocks propagating along the inner bend. Predictions from 3-shock theory (Courant & Friedrichs 1948) of the Mach number at the outer wall are consistently higher than those from Whitham's analysis. In turn, the latter tends to slightly overestimate the strength of the wall shock.A model is developed, based on an extension of Whitham's analysis, and is shown to predict the length of the Mach stem produced by shocks of M0 > 2 over the initial stages of the bend.

Effect of Draw Bead Height on Wall Features in Rectangular Deep-Drawing Process Using Finite Element Method

2011 ◽  
Vol 264-265 ◽  
pp. 1580-1585 ◽  
Author(s):  
Sutasn Thipprakmas
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Tensile Stress ◽  
Fem Simulation ◽  
Bead Geometry ◽  
Concave Wall ◽  
Convex Wall ◽  
Simulation Results ◽  
Bead Height ◽  
Element Method

Concave/convex wall features are usually generated in the deep-drawn parts with complicated geometry, especially the difficult-to-deep draw materials. The application of the draw bead could reduce the concave/convex wall features. However, it is difficult to determine the suitable draw bead geometry and its position to obtain a straight wall. In this study, the effects of draw bead height were investigated using the finite element method (FEM) and experiments. The application of the draw bead and the effects of its height on the concave/convex wall features could be theoretically clarified on the basis of principal stress distribution. The application of draw bead led to the decrease in tensile stress in the direction of punch movement and also increased in the tensile stress distributed to the corner zone; therefore, the concave wall feature decreased. In addition, this feature decreased as the draw bead height increased. However, the application of a very large draw bead height resulted in a convex feature. The FEM simulation results were validated by experiments in the following two cases, i.e., without and with draw bead formations. With reference to the material thickness distribution, the FEM simulation results showed a good agreement with experimental results.

Row-of-Holes Film Cooling of Curved Walls at Low Injection Angles

1997 ◽  
Vol 119 (3) ◽  
pp. 574-579 ◽  
Author(s):  
R. J. Goldstein ◽  
L. D. Stone
Keyword(s):  
Film Cooling ◽  
Film Cooling Effectiveness ◽  
Injection Angle ◽  
Local Boundary ◽  
Vortex Interactions ◽  
Concave Wall ◽  
Convex Wall ◽  
Lift Off ◽  
Density Ratios ◽  
Curved Walls

Film cooling effectiveness data are presented against a backdrop of ammonia-diazo flow visualizations for row-of-holes injection along a convex wall and a concave wall at angles of 15, 25, and 45 deg to the mainstream and at density ratios of approximately one and two. Injection angle effects vary with the rate of injection: At low blowing rates the injection angle is unimportant, at moderate blowing rates the shallower angles provide better effectiveness, and at high blowing rates a steeper injection angle sometimes provides better effectiveness. The condition of the local boundary layer, the severity of jet lift-off, and the strength of vortex interactions among the bound vortices of neighboring jets are key considerations in interpreting the data.

Affect of Part Geometry on Wall Features in Rectangular Deep-Drawing Processes Using Finite Element Method

2009 ◽  
Vol 410-411 ◽  
pp. 579-585 ◽  
Author(s):  
Sutasn Thipprakmas
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Complex Geometry ◽  
Thickness Distribution ◽  
Cost Effective ◽  
Bead Formation ◽  
Concave Wall ◽  
Convex Wall ◽  
Forming Defects ◽  
Element Method

High-quality stamped parts using cost-effective production technique are increasingly required, especially in parts with complex geometry wherein forming defects are easily generated. In this study, the concave and convex wall features were investigated for a stainless steel rectangular tray using the finite element method and related experiments. The concave and convex wall phenomena were theoretically clarified on the basis of stress distribution. The effects of tray geometry were also investigated. Increasing both the rectangle size and depth of tray, together with a decrease in the corner radius, resulted in an increase in concave wall generation. However, the effects of increasing the length or width of the rectangle affecting the concave wall were independent of each other. In addition, the application of a very large depth of tray resulted in a convex feature. The results showed that it is difficult to achieve a straight wall on both the ‘length’ and ‘width’ sides without the use of draw bead. The finite element simulation results showed a reasonable agreement with the experimental results, with reference to the material thickness distribution in both the cases of: absence of the draw bead formation; and presence of the draw-bead formation.

Sign in / Sign up

Export Citation Format

Share Document