Effect of Three-Dimensional Surface Topography on Gas Flow in Rough Micronozzles

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Han Yan ◽  
Wen-Ming Zhang ◽  
Zhi-Ke Peng ◽  
Guang Meng
Keyword(s):  
Surface Topography ◽  
Gas Flow ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Slip Model ◽  
First Order ◽  
3D Surface Topography ◽  
Good Agreement

The gas flow characteristics in rectangular cross section converging–diverging micronozzles incorporating the effect of three-dimensional (3D) rough surface topography are investigated. The fractal geometry is utilized to describe the multiscale self-affine roughness. A first-order slip model suitable for rough walls is adopted to characterize the slip velocities. The flow field in micronozzles is analyzed by solving 3D Navier–Stokes (N–S) equation. The results show that the dependence of mass flow rate on the pressure difference has a good agreement with the reported results. The presence of surface topography obviously perturbs the gas flow near the wall. Moreover, as the surface roughness height increases, this perturbation induces the supersonic “multiwaves” phenomenon in the divergent region, in which the Mach number fluctuates. In addition, the effect of 3D surface topography on performance is also investigated.

Numerical Study on Supersonic Combustor with an Allotype Cavity

2014 ◽  
Vol 694 ◽  
pp. 187-192
Author(s):  
Jin Xiang Wu ◽  
Jian Sun ◽  
Xiang Gou ◽  
Lian Sheng Liu
Keyword(s):  
Alternative Model ◽  
Numerical Study ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Experimental Result ◽  
Navier Stokes ◽  
Cold Flow ◽  
Hypersonic Inlet ◽  
Good Agreement

The three-dimensional coupled explicit Reynolds Averaged Navier–Stokes (RANS) equations and the two equation shear-stress transport k-w (SST k-w) model has been employed to numerically simulate the cold flow field in a special-shaped cavity-based supersonic combustor. In a cross-section shaped rectangular, hypersonic inlet with airflow at Mach 2.0 chamber, shock structures and flow characteristics of a herringbone-shaped boss and a herringbone-shaped cavity models were discussed, respectively. The results indicate: Firstly, according to the similarities of bevel-cutting shock characteristics between the boss case and the cavity case, the boss structure can serve as an ideal alternative model for shear-layer. Secondly, the eddies within cavity are composed of herringbone-spanwise vortexes, columnar vortices in the front and main-spanwise vortexes in the rear, featuring tilting, twisting and stretching. Thirdly, the simulated bottom-flow of cavity is in good agreement with experimental result, while the reverse flow-entrainment resulting from herringbone geometry and pressure gradient. However, the herringbone-shaped cavity has a better performance in fuel-mixing.

Numerical Analysis of Rarefaction and Compressibility Effects in Bent Microchannels

2010 ◽  
Author(s):  
O. Rovenskaya ◽  
G. Croce
Keyword(s):  
Gas Flow ◽  
Flow Characteristics ◽  
Wall Slip ◽  
Outer Wall ◽  
Slip Boundary Condition ◽  
Central Line ◽  
Navier Stokes ◽  
Strong Impact ◽  
First Order ◽  
Slip Boundary

Numerical investigation of a gas flow through microchannels with a sharp, 90 degrees bend is carried out using Navier-Stokes (N-S) equations with the classical Maxwell first-order slip boundary condition, including the tangential gradient effect due to the wall curvature, and Smoluchowski first order temperature jump definition. The details of the flow structure near the corner are analyzed, investigating the competing effects of rarefaction and compressibility on the channel performances. The flow characteristics in terms of velocity profiles, slip velocity distribution along inner and outer wall, pressure, average Mach number along central line of the channel have been presented. The results showed that impact of the bend on the channel performances is smaller at high rarefaction levels. The behaviour of pressure and velocity away from the bend is similar to that of a straight microchannel; however, the asymmetry in the flow at the bend, with high velocities and high velocity gradients on its inner side, has a strong impact on wall slip velocities. The presence of a recirculation is detected on both the inner and outer walls of the corner for larger Reynolds. However, rarefaction may delay the onset of recirculation. It is also observed that the mass flux through a bend microchannel can even be slightly larger than that through a straight microchannel of the same length and subjected to the same pressure difference.

Three-dimensional separated flow structure over a cylinder with a hemispherical cap

1996 ◽  
Vol 324 ◽  
pp. 83-108 ◽  
Author(s):  
T. Hsieh ◽  
K. C. Wang
Keyword(s):  
Structural Characteristics ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Horseshoe Vortex ◽  
Navier Stokes ◽  
Water Tunnel ◽  
Separation Sequence ◽  
Vortex Systems ◽  
Good Agreement

Thin-layer Navier–Stokes solutions are obtained for an incompressible laminar flow over a hemisphere–cylinder at 10°, 30° and 50° incidence to exhibit some three-dimensional separated flow characteristics. Some of the results are compared with a previous water-tunnel investigation for the same body geometry. Good agreement is found, even for some detailed features. Although the geometry is relatively simple, the separated flow surprisingly embraces a number of intricate structural characteristics unique to three-dimensional flows. Particularly noteworthy are the separation sequence at increasing incidence, tornado-like vortices, outward-spiralling vortices, limit cycles, coaxial counter-spiralling patterns and horseshoe vortex systems. Physical insights to these new features are offered.

Mechanism and Flow Control on the Mismatching of Impeller and Vaned Diffuser Caused by Inlet Prewhirl for Centrifugal Compressors

2016 ◽  
Author(s):  
Qiangqiang Huang ◽  
Xinqian Zheng ◽  
Aolin Wang
Keyword(s):  
Flow Control ◽  
Control Method ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vaned Diffuser ◽  
Inlet Distortion ◽  
Computational Fluid Dynamics Cfd ◽  
Stagger Angle ◽  
Good Agreement ◽  
Matching Relation

Air often flows into compressors with inlet prewhirl, because it will obtain a circumferential component of velocity via inlet distortion or swirl generators such as inlet guide vanes. A lot of research has shown that inlet prewhirl does influence the characteristics of components, but the change of the matching relation between the components caused by inlet prewhirl is still unclear. This paper investigates the influence of inlet prewhirl on the matching of the impeller and the diffuser and proposes a flow control method to cure mismatching. The approach combines steady three-dimensional Reynolds-averaged Navier-Stokes (RANS) simulations with theoretical analysis and modeling. The result shows that a compressor whose impeller and diffuser match well at zero prewhirl will go to mismatching at non-zero prewhirl. The diffuser throat gets too large to match the impeller at positive prewhirl and gets too small for matching at negative prewhirl. The choking mass flow of the impeller is more sensitive to inlet prewhirl than that of the diffuser, which is the main reason for the mismatching. To cure the mismatching via adjusting the diffuser vanes stagger angle, a one-dimensional method based on incidence matching has been proposed to yield a control schedule for adjusting the diffuser. The optimal stagger angle predicted by analytical method has good agreement with that predicted by computational fluid dynamics (CFD). The compressor is able to operate efficiently in a much broader flow range with the control schedule. The flow range, where the efficiency is above 80%, of the datum compressor and the compressor only employing inlet prewhirl and no control are just 25.3% and 31.8%, respectively. For the compressor following the control schedule, the flow range is improved up to 46.5%. This paper also provides the perspective of components matching to think about inlet distortion.

Extended Thermodynamic Approach for Non-Equilibrium Gas Flow

2013 ◽  
Vol 13 (5) ◽  
pp. 1330-1356 ◽  
Author(s):  
G. H. Tang ◽  
G. X. Zhai ◽  
W. Q. Tao ◽  
X. J. Gu ◽  
D. R. Emerson
Keyword(s):  
Heat Transfer ◽  
Equilibrium State ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Flow Characteristics ◽  
Bimodal Distribution ◽  
Thermodynamic Approach ◽  
Navier Stokes ◽  
Extended Thermodynamic ◽  
Non Equilibrium

AbstractGases in microfluidic structures or devices are often in a non-equilibrium state. The conventional thermodynamic models for fluids and heat transfer break down and the Navier-Stokes-Fourier equations are no longer accurate or valid. In this paper, the extended thermodynamic approach is employed to study the rarefied gas flow in microstructures, including the heat transfer between a parallel channel andpressure-driven Poiseuille flows through a parallel microchannel andcircular microtube. The gas flow characteristics are studied and it is shown that the heat transfer in the non-equilibrium state no longer obeys the Fourier gradient transport law. In addition, the bimodal distribution of streamwise and spanwise velocity and temperature through a long circular microtube is captured for the first time.

A Large Measuring Range Profilometer for Three-Dimensional Surface Topography Measurement

2007 ◽  
Vol 364-366 ◽  
pp. 750-755 ◽  
Author(s):  
Xu Dong Yang ◽  
Jia Chun Li ◽  
Tie Bang Xie
Keyword(s):  
Surface Topography ◽  
Three Dimensional ◽  
Displacement Sensor ◽  
Resistance Force ◽  
Sampling Point ◽  
Measuring Range ◽  
3D Surface Topography ◽  
Control Circuits ◽  
Industrial Control Computer ◽  
Zero Offset

A novel profilometer for three-dimensional (3D) surface topography measurement is presented. The profilometer has large measuring range, high precision and small measuring touch force. It is composed of a two-dimensional (2D) displacement sensor, a 3D platform based on vertical scanning, measuring and control circuits and an industrial control computer. When a workpiece is measured, the vertical undulation of the profile at a sampling point leads to a zero offset of the 2D displacement sensor. According to the zero offset, a piezoelectric actuator and a servo motor drive the vertical scanning platform to move vertically to ensure that the lever returns to its balance position. So the non-linear error caused by the rotation of the lever is very small even if the measuring range is large. When the stylus barges up against a steep wall, the horizontal resistance force results in another zero offset of the 2D displacement sensor. If the zero offset exceeds a quota, the vertical scanning platform descends to make the stylus climb the steep wall successfully. According to the theoretical and experimental analysis, the profilometer can measure roughness, profile of sphere, step, groove and other 3D surfaces with curvature precisely.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

Numerical Modelling of Circulation in Lake Sperillen, Norway

2000 ◽  
Vol 31 (1) ◽  
pp. 57-72 ◽  
Author(s):  
N. R. B. Olsen ◽  
D. K. Lysne
Keyword(s):  
Numerical Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Field Measurements ◽  
Navier Stokes ◽  
Water Current ◽  
Simple Method ◽  
Vertical Temperature Profile ◽  
Navier Stokes Equations ◽  
Good Agreement

A three-dimensional numerical model was used to model water circulation and spatial variation of temperature in Lake Sperillen in Norway. A winter situation was simulated, with thermal stratification and ice cover. The numerical model solved the Navier-Stokes equations on a 3D unstructured non-orthogonal grid with hexahedral cells. The SIMPLE method was used for the pressure coupling and the k-ε model was used to model turbulence, with a modification for density stratification due to the vertical temperature profile. The results were compared with field measurements of the temperature in the lake, indicating the location of the water current. Reasonably good agreement was found.

scholarly journals ICCM2015: A Comparison of RANS and LES Computational Methods in Analyzing Ventilation Flow Through a Room Fitted with a Two-Sided Windcatcher

2017 ◽  
Vol 14 (03) ◽  
pp. 1750021 ◽  
Author(s):  
A. Niktash ◽  
B. P. Huynh
Keyword(s):  
Natural Ventilation ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Interior Space ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Cfd Method ◽  
Good Agreement

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

Leakage Monitoring in Static Sealing Interface Based on Three Dimensional Surface Topography Indicator

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Yiping Shao ◽  
Yaxiang Yin ◽  
Shichang Du ◽  
Tangbin Xia ◽  
Lifeng Xi
Keyword(s):  
Surface Topography ◽  
Three Dimensional ◽  
Machining Process ◽  
Void Volume ◽  
Engineering Practice ◽  
High Definition ◽  
Monitoring Method ◽  
3D Surface ◽  
3D Surface Topography ◽  
Leakage Monitoring

Leakage directly affects the functional behavior of a product in engineering practice, and surface topography is one of the main factors in static seal to prevent leakage. This paper aims at monitoring the leakage in static sealing interface, using three-dimensional (3D) surface topography as an indicator. The 3D surface is measured by a high definition metrology (HDM) instrument that can generate millions of data points representing the entire surface. The monitoring approach proposes a series of novel surface leakage parameters including virtual gasket, contact area percentage (CAP), void volume (VV), and relative void volume (SWvoid) as indicators. An individual control chart is adopted to monitor the leakage surface of the successive machining process. Meantime, based on the Persson contact mechanics and percolation theory, the threshold of leakage parameter is found using finite element modeling (FEM). Experimental results indicate that the proposed monitoring method is valid to precontrol the machining process and prevent leakage occurring.

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