scholarly journals Screech tones from rectangular jets with spanwise oblique shock-cell structures

1997 ◽  
Vol 330 ◽  
pp. 141-168 ◽  
Author(s):  
GANESH RAMAN
Keyword(s):  
Aspect Ratio ◽  
Fatigue Failure ◽  
Cell Structure ◽  
Oblique Shock ◽  
Spanwise Direction ◽  
Shock Cell ◽  
Cell Spacing ◽  
Cell Structures ◽  
Shaped Nozzle ◽  
Amplitude Mode

Understanding screech is especially important for the design of advanced aircraft because screech can cause sonic fatigue failure of aircraft structures. Although the connection between shock-cell spacing and screech frequency is well understood, the relation between non-uniformities in the shock-cell structures and the resulting amplitude, mode, and steadiness of screech have remained unexplored. This paper addresses the above issues by intentionally producing spanwise (larger nozzle dimension) variations in the shock-cell structures and studying the resulting spanwise screech mode. The spanwise-oblique shock-cell structures were produced using imperfectly expanded convergent–divergent rectangular nozzles (aspect ratio = 5) with non-uniform exit geometries. Three geometries were studied: (a) a nozzle with a spanwise uniform edge, (b) a nozzle with a spanwise oblique (single-bevelled) edge, and (c) a nozzle that had two spanwise oblique (double-bevelled) cuts to form an arrowhead-shaped nozzle. For all nozzles considered, the screech mode was antisymmetric in the transverse (smaller nozzle dimension) direction allowing focus on changes in the spanwise direction. Three types of spanwise modes were observed: symmetric (I), antisymmetric (II), and oblique (III). The following significant results emerged: (i) for all cases the screech mode corresponds with the spanwise shock-cell structure, (ii) when multiple screech modes are present, the technique presented here makes it possible to distinguish between coexisting and mutually exclusive modes, (iii) the strength of shocks 3 and 4 influences the screech source amplitude and determines whether screech is unsteady. The results presented here offer hope for a better understanding of screech and for tailoring shock-containing jets to minimize fatigue failure of aircraft components.

Computational and Experimental Studies of Cellular Samples Manufactured Using Additive Methods for Use in Advanced Lightweight Designs of Engine Parts

2020 ◽  
Author(s):  
Liubov Magerramova ◽  
Michael Volkov ◽  
Oleg Volgin ◽  
Pavel Kolos
Keyword(s):  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Cell Structure ◽  
Experimental Studies ◽  
Cellular Structures ◽  
Uniaxial Tensile ◽  
Porous Structures ◽  
Lattice Cell ◽  
Cell Structures ◽  
Homogeneous Materials

Abstract The use of cellular structures is one way to reduce the weight of engine parts. Cellular structures are used to provide rigidity and strength for parts subject to compression, bending, and shock loads. Failure of the individual elements of a lattice/cell structure does not result in the destruction of the entire part; this stands in contrast to the structure of a conventional homogeneous metal object, in which cracks will continue to increase with increasing load, causing the destruction of the entire part. Lattice/cell structures have relatively high characteristics of rigidity and strength, excellent thermal insulation properties, energy absorption characteristics, and high fatigue resistance. The use of this type of structure in engine part construction opens up new opportunities for advanced aviation applications. However, the deformation behavior of porous and metallic structures differs significantly from that of conventional homogeneous materials. Samples with cellular and porous structures are themselves designs. Therefore, procedures for strength testing and interpretation of experimental results for cellular and porous structures differ from those for samples derived from homogeneous materials. The criteria for determining the properties of cellular structures include density, stiffness, ability to accumulate energy, etc. These parameters depend on the configuration of the cells, the size of each cell, and the thickness of the connecting elements. Mechanical properties of cellular structures can be established experimentally and confirmed numerically. Special cellular specimens have been designed for uniaxial tensile, bending, compression, shear, and low-cycle fatigue testing. Several variants of cell structures with relative densities ranging from 13 to 45% were considered. Specifically, the present study examined the stress-strain states of cell structures from brands “CobaltChrome MP1” powder compositions obtained by laser synthesis on an industrial 3D printer Concept Laser M2 Cusing Single Laser 400W. Numerical simulations of the tests were carried out by the finite element method. Then, the most rational cellular structures in terms of mass and strength were established on the basis of both real and numerical experiments.

Technological Exercise of Cell Structure Forming

2017 ◽  
Vol 736 ◽  
pp. 122-126 ◽  
Author(s):  
S.N. Larin ◽  
V.I. Platonov ◽  
G.A. Nuzgdin
Keyword(s):  
Liquid Fuel ◽  
Cell Structure ◽  
Experimental Studies ◽  
Single Layer ◽  
Processing Parameters ◽  
Utilization Factor ◽  
Specific Strength ◽  
Cell Structures ◽  
Critical Strain Rate ◽  
Material Utilization

Single-layer and multi-layer cell structures are used for manufacturing of shells of liquid fuel tankers, as well as of "dry" shells of products, wings, fairings, etc. However, conventional methods of production by means of milling do not allow achieving the required specific strength. In this connection, diffusion bonding by means of gas pressure and gas forming at specified temperature and speed conditions are extremely important. Studies conducted by authors help model the processes and calculate the necessary processing parameters: pressure, critical strain rate, deformation rate (deformation time). This paper describes the manufacturing technology for these products, in which the solutions are based on theoretical and experimental studies, which provide: an increase in specific strength; reduction in weight of the product; reduction of labor intensity and increase in material utilization factor.

Cell structure and mechanical properties of microcellular PLA foams prepared via autoclave constrained foaming

2020 ◽  
pp. 026248932093032
Author(s):  
Jinwei Chen ◽  
Ling Yang ◽  
Dahua Chen ◽  
Qunshan Mai ◽  
Meigui Wang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cell Size ◽  
Cell Structure ◽  
Saturation Pressure ◽  
Tensile Modulus ◽  
Cell Structures ◽  
Wide Range ◽  
The Mean ◽  
Constrained Foaming ◽  
The Relationship

Microcellular polylactic acid (PLA) foams with various cell size and cell morphologies were prepared using supercritical carbon dioxide (sc-CO2) solid-state foaming to investigate the relationship between the cell structure and mechanical properties. Constrained foaming was used and a wide range of cell structures with a constant porosity of ∼75% by tuning saturation pressure (8–24 MPa) was developed. Experiments varying the saturation pressure while holding other variables’ constant show that the mean cell size and the mean cell wall thickness decreased, while the cell density and the open porosity increased with increase of pressure. Tensile modulus of PLA foams decreased with increasing the saturation pressure, but the specific tensile modulus of PLA foams was still 15–80% higher than that of solid PLA. Tensile strength and elongation at break first increased with increasing saturation pressure up to 16 MPa and then decreased with further increasing saturation pressure (20 MPa and 24 MPa) at which opened-cell structure produced. Compressive modulus, compressive strength, and compressive yield stress also followed the same variation trend. The results indicated that not only cell size plays an important role in properties of PLA foams but also cell morphology can influence these properties significantly.

Noisefield of Underexpanded Notched Circular-Slot Jets

2002 ◽  
Vol 33 (6) ◽  
pp. 9-23
Author(s):  
S.B. Verma ◽  
E. Rathakrishnan
Keyword(s):  
Acoustic Emission ◽  
Aspect Ratio ◽  
Cell Length ◽  
Emission Characteristics ◽  
Far Field ◽  
Shock Cell ◽  
Acoustic Spectrum ◽  
Compression Waves ◽  
Noise Field ◽  
Notch Geometry

The effect of notches on the flow and noise field of jets from circular-slots is experimentally investigated. Three types of slot geometries, namely, semicircular, triangular and square are studied. The results demonstrate that the presence of the notch introduces a slight aspect-ratio in the initial circular-slot geometry so that the notched jet exhibits characteristics, similar to jets exiting from non-circular geometries. At underexpanded condition, additional expansion and compression waves are observed to emanate from the region of notches that modifies the jet development and results in a reduction in the average shock-cell length, which is accompanied by a reduction in far-field shock associated noise. The acoustic spectrum of the radiated shock noise indicates that notch geometry variation strongly alters the acoustic emission characteristics of these jets both in the screech component and broadband shock associated noise.

scholarly journals Density measurements for rectangular free jets using background-oriented schlieren

2013 ◽  
Vol 117 (1194) ◽  
pp. 771-785 ◽  
Author(s):  
T. J. Tipnis ◽  
M. V. Finnis ◽  
K. Knowles ◽  
D. Bray
Keyword(s):  
Supersonic Jet ◽  
Digital Camera ◽  
Shock Cell ◽  
Axisymmetric Jets ◽  
Cell Spacing ◽  
Optical Alignment ◽  
Background Oriented Schlieren ◽  
Set Up ◽  
Axis Switching ◽  
Good Agreement

AbstractAn experimental study incorporating the use of the Background-Oriented Schlieren (BOS) technique was performed to measure the density field of a rectangular supersonic jet. This technique is easier to set up than conventional schlieren since the optical alignment involving the various mirrors, lenses and knife-edge is replaced by a background pattern and a single digital camera. The acquired images which contain information of density gradients in the flow are solved as a Poisson equation and further processed using deconvolution and tomographic algorithms to generate a 3D domain which contains information about the actual density. 2D slices can then be extracted to quantitatively visualise the density along any required planes. The results from supersonic axisymmetric jets are used for validation of the code; these show excellent agreement with pre-validated CFD data. The results for a rectangular supersonic jet are then obtained. These show good agreement with the CFD data, in terms of shock-cell spacing and overall structure of the jet. The technique has proved useful for investigating axis-switching, a phenomenon generally associated with non-axisymmetric jets.

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.

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