scholarly journals Three-Dimensional Visualization of Shock Cell Structure and Screech Tone Emission in Underexpanded Circular Jet

2022 ◽  
Vol 10 (01) ◽  
pp. 1-11
Author(s):  
Keita Ozawa ◽  
Takayuki Yamagata ◽  
Nobuyuki Fujisawa
Keyword(s):  
Cell Structure ◽  
Three Dimensional ◽  
Shock Cell ◽  
Screech Tone ◽  
Tone Emission

scholarly journals Assessment of Short Rectangular-Tab Actuation of Supersonic Jet Mixing

Actuators ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 72 ◽  
Author(s):  
Abhash Ranjan ◽  
Mrinal Kaushik ◽  
Dipankar Deb ◽  
Vlad Muresan ◽  
Mihaela Unguresan
Keyword(s):  
Coming Out ◽  
Nozzle Exit ◽  
Stokes Equations ◽  
Cell Structure ◽  
Pressure Ratio ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Shock Cell ◽  
Jet Mixing ◽  
Nozzle Pressure

This work explores the extent of jet mixing for a supersonic jet coming out of a Mach 1.8 convergent-divergent nozzle, controlled with two short rectangular vortex-generating actuators located diametrically opposite to each other with an emphasis on numerical methodology. The blockage ratio offered by the tabs is around 0.05. The numerical investigations were carried out by using a commercial computational fluid dynamics (CFD) package and all the simulations were performed by employing steady Reynolds-averaged Navier–Stokes equations and shear-stress transport k−ω turbulence model on a three-dimensional computational space for more accuracy. The numerical calculations are administered at nozzle pressure ratios (NPRs) of 4, 5, 6, 7 and 8, covering the overexpanded, the correctly expanded and the underexpanded conditions. The centerline pressure decay and the pressure profiles are plotted for both uncontrolled and the controlled jets. Numerical schlieren images are used to capture the barrel shock, the expansion fans and the Mach waves present in the flow field. Mach contours are also delineated at varying NPRs indicating the number of shock cells, their length and the variation of the shock cell structure and strength, to substantiate the prominent findings. The outcomes of this research are observed to be in sensible concurrence with the demonstrated exploratory findings. A reduction in the jet core length of 75% is attained with small vortex-generating actuators, compared to an uncontrolled jet, corresponding to nozzle pressure ratio 5. It was also seen that the controlled jet gets bifurcated downstream of the nozzle exit at a distance of about 5 D, where D is the nozzle exit diameter. Furthermore, it was fascinating to observe that the jet spread increases downstream of the nozzle exit for the controlled jet, as compared to the uncontrolled jet at any given NPR.

The Development of an Automatic Three-Dimensional Mesh Generator via Modified Ray Casting

1992 ◽  
Author(s):  
Cengiz Yeker ◽  
Ibrahim Zeid
Keyword(s):  
Finite Elements ◽  
Cell Structure ◽  
Three Dimensional ◽  
Ray Casting ◽  
Solid Object ◽  
Casting Technique ◽  
Element Size ◽  
A Cell ◽  
Conforming Meshes ◽  
Representation Scheme

Abstract A fully automatic three-dimensional mesh generation method is developed by modifying the well-known ray casting technique. The method is capable of meshing objects modeled using the CSG representation scheme. The input to the method consists of solid geometry information, and mesh attributes such as element size. The method starts by casting rays in 3D space to classify the empty and full parts of the solid. This information is then used to create a cell structure that closely models the solid object. The next step is to further process the cell structure to make it more succinct, so that the cells close to the boundary of the solid object can model the topology with enough fidelity. Moreover, neighborhood relations between cells in the structure are developed and implemented. These relations help produce better conforming meshes. Each cell in the cell structure is identified with respect to a set of pre-defined types of cells. After the identification process, a normalization process is developed and applied to the cell structure in order to ensure that the finite elements generated from each cell conform to each other and to other elements produced from neighboring cells. The last step is to mesh each cell in the structure with valid finite elements.

Development of Scaffold Building Units and Assembly for Tissue Engineering Using Fused Deposition Modelling

2009 ◽  
Vol 83-86 ◽  
pp. 269-274 ◽  
Author(s):  
Syed H. Masood ◽  
Kadhim Alamara
Keyword(s):  
Tissue Engineering ◽  
Pore Size ◽  
Fused Deposition Modeling ◽  
Porous Scaffold ◽  
Cell Structure ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Fused Deposition Modelling ◽  
Fused Deposition ◽  
Unit Cells

In tissue engineering (TE), a porous scaffold structure of biodegradable material is required as a template to guide the proliferation, growth and development of cells appropriately in three dimensions. The scaffold must meet design requirements of appropriate porosity, pore size and interconnected structure to allow cell proliferation and adhesion. This paper presents a methodology for design and manufacture of TE scaffolds with varying porosity by employing open structure building units and Fused Deposition Modeling (FDM) rapid prototyping technique. A computer modeling approach for constructing and assembly of three-dimensional unit cell structure is presented to provide a solution of scaffolds design that can potentially meet the diverse requirements of TE applications. A parametric set of open polyhedral unit cells is used to assist the user in designing the required micro-architecture of the scaffold with required porosity and pore size and then the Boolean operation is used to create the scaffold of a given CAD model from the designed microstructure. The procedure is verified by fabrication of physical scaffolds using the commercial FDM system.

Propagation of Multiple Short-Length-Scale Stall Cells in an Axial Compressor Rotor

1999 ◽  
Vol 122 (1) ◽  
pp. 45-54 ◽  
Author(s):  
M. Inoue ◽  
M. Kuroumaru ◽  
T. Tanino ◽  
M. Furukawa
Keyword(s):  
Cell Structure ◽  
Three Dimensional ◽  
Stable State ◽  
Axial Compressor ◽  
Large Cell ◽  
Short Length ◽  
Length Scale ◽  
Compressor Rotor ◽  
Double Phase ◽  
Stall Cells

Evolution and structure of multiple stall cells with short-length-scale in an axial compressor rotor have been investigated experimentally. In a low-speed research compressor rotor tested, a short-length-scale stall cell appeared at first, but did not grow rapidly in size, unlike a so-called “spike-type stall inception” observed in many multistage compressors. Alternatively, the number of cells increased to a certain stable state (a mild stall state) under a fixed throttle condition. In the mild stall state the multiple stall cells, the size of which was on the same order of the inception cell (a few blade spacings), were rotating at 72 percent of rotor speed and at intervals of 4.8 blade spacings. With further throttling, a long-length-scale wave appeared overlapping the multiple short-length-scale waves, then developed to a deep stall state with a large cell. In order to capture the short-length-scale cells in the mild stall state, a so-called “double phase-locked averaging technique” has been developed, by which the flow field can be measured phase locked to both the rotor and the stall cell rotation. Then, time-dependent ensemble averages of the three-dimensional velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and the pressure distributions on the casing wall with high-response pressure transducers. By a physically plausible explanation for the experimental results, a model for the flow mechanism of the short-length-scale stall cell has been presented. The distinctive feature of the stall cell structure is on the separation vortex bubble with a leg traveling ahead of the rotor, with changing the blade in turn on which the vortex leg stands. [S0889-504X(00)00701-7]

The evolution of the initial flow structures of a highly under-expanded circular jet

2019 ◽  
Vol 871 ◽  
pp. 305-331 ◽  
Author(s):  
Huan-Hao Zhang ◽  
Nadine Aubry ◽  
Zhi-Hua Chen ◽  
Wei-Tao Wu ◽  
Sha Sha
Keyword(s):  
Vortex Ring ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Secondary Vortex ◽  
Shock Cell ◽  
Initial Flow ◽  
Turbulence Transition ◽  
Circular Jets ◽  
Generation Mechanisms

The three-dimensional flow characteristics of the compressible vortex ring generated by under-expanded circular jets with two typical pressure ratios, i.e. $n=1.4$ (moderate) and 4.0 (high), are investigated numerically with the use of large-eddy simulations. Our results illustrate that these two pressure ratios correspond to different shock structures (shock cell and Mach disc, respectively) within the jet. These two typical types of flow structures and characteristics are discussed and validated with experiments, and the different generation mechanisms of the secondary vortex rings are compared. Moreover, detailed information about the evolution of the secondary vortex ring, primary vortex ring and turbulence transition features, including the radial and azimuthal modes, is investigated. The geometric features and mixing effects of the jets are also explored.

Studies on high speed jets from nozzles with internal grooves

2004 ◽  
Vol 108 (1079) ◽  
pp. 43-50 ◽  
Author(s):  
S. Elangovan ◽  
E. Rathakrishnan
Keyword(s):  
High Speed ◽  
Cell Structure ◽  
Pressure Profile ◽  
Equivalent Diameter ◽  
Streamwise Vortices ◽  
Shock Cell ◽  
Underexpanded Jets ◽  
Pitot Pressure ◽  
Mean Pressure ◽  
The Mean

Experiments were carried out on jets issuing from circular nozzles with grooved exits and the results compared with those of the plain nozzle. The plain nozzle had an exit diameter of 10mm. Because of the introduction of semi-circular grooves at the exit, the effective or equivalent diameter of the grooved nozzles was 10·44mm. The groove lengths were varied as 3, 5 and 8mm. The nozzles were operated at fully expanded sonic and underexpanded exit conditions. The corresponding fully expanded Mach numbers were 1·0 and 1·41. The shock cell structure of the underexpanded jets from grooved nozzles appeared to be weaker than that of the plain nozzle, as indicated by lesser amplitudes of the cyclic variation of the Pitot pressure. The iso-Mach contours indicate that the jet spread along the grooved plane is significantly higher than that along the ungrooved plane. Off-centre peaks were observed in the mean pressure profile of underexpanded jets from grooved nozzles. They were probably due to the streamwise vortices shed from the grooves.

Schlieren 3D-CT Measuremsnt of Instantaneous Density Distributions of the Shock-cell Structure of Under-Expanded Supersonic Jets

2016 ◽  
Vol 2016 (0) ◽  
pp. J0510203
Author(s):  
Ahmad Z. NAZARI ◽  
Naoki HAYASHI ◽  
Yuta ISHIKO ◽  
Kimihiro NAGASE ◽  
Kazuma KAKIMOTO ◽  
...  
Keyword(s):  
Cell Structure ◽  
Supersonic Jets ◽  
3D Ct ◽  
Shock Cell ◽  
Density Distributions

Structure-unit cell-based approach on three-dimensional representative braided preforms from four-step braiding: Experimental determination of effects of structure-process parameters on predetermined yarn path

2011 ◽  
Vol 82 (3) ◽  
pp. 220-241 ◽  
Author(s):  
Kadir Bilisik ◽  
Nesrin Sahbaz
Keyword(s):  
Cell Structure ◽  
Three Dimensional ◽  
Unit Cell ◽  
Number Of Layers ◽  
Cell Structures ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Surface Angle ◽  
Unit Cell Structure

The aim of this study was to understand the effects of braid pattern and the number of layers on three-dimensional (3D) braided unit cell structures. Various unit cell-based representative 3D braided preforms were developed. Data generated from these structures included unit cell dimensions, yarn angle, and yarn length in the unit cell structures. It was shown that braid patterns affected the 3D braided unit cell structures. The 1 × 1 braid pattern made fully interconnected integral 3D braided unit cell structures, whereas the 2 × 1 braid pattern created disconnected braid layers that were connected to the structures edges. When the number of layers increased, 3D braided unit cell thickness also increased. Braid pattern slightly affected the braider yarn angle, whereas the number of layers did not influence it. It was observed that the number of layers considerably affected the yarn length in the unit cell structure. Increasing the layer number from five to 10 layers created a yarn path in the unit cell edge regions called the ‘multilayer yarn length’. This yarn path was not observed below five-layer 3D braided unit cell structures. In jamming conditions, minimum jamming decreased the width of the unit cell structure, but maximum jamming increased its width. On the other hand, minimum jamming decreased the surface angle of the unit cell structure, whereas maximum jamming increased the surface angle. In addition, it was realized that jamming conditions influenced the density of the unit cell but did not affect the yarn length in the unit cell structures.

Visualization Studies of a Shear Driven Three-Dimensional Recirculating Flow

1984 ◽  
Vol 106 (1) ◽  
pp. 21-27 ◽  
Author(s):  
J. R. Koseff ◽  
R. L. Street
Keyword(s):  
Cell Structure ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Uniform Density ◽  
Driven Cavity ◽  
Recirculating Flow ◽  
Circulation Cell ◽  
Speed Range ◽  
Main Circulation ◽  
Cavity Width

A facility has been constructed to study shear-driven, recirculating flows. In this particular study, the circulation cell structure in the lid-driven cavity is studied as a function of the speed of the lid which provides the shearing force to a constant and uniform density fluid. The flow is three-dimensional and exhibits regions where Taylor-type instabilities and Taylor-Go¨rtler-like vortices are present. One main circulation cell and three secondary cells are present for the Reynolds number (based on cavity width and lid speed) range considered, viz., 1000–10000. The flows becomes turbulent at Reynolds numbers between 6000 to 8000. The transverse fluid motions (in the direction perpendicular to the lid motion) are significant. In spite of this, some key results from two-dimensional numerical simulations agree well with the results of the present cavity experiments.

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