scholarly journals 2.5D les simulation of an airfoil shock wave reduction by using porous media

2020 ◽  
Vol 32 ◽  
pp. 122-133
Author(s):  
Ion Malael ◽  
Ioana Octavia Bucur ◽  
Valeriu Dragan
Keyword(s):  
Shock Wave ◽  
Porous Media ◽  
Shock Waves ◽  
High Speed ◽  
Aerodynamic Coefficients ◽  
Qualitative Comparison ◽  
Ansys Fluent ◽  
Motion Equations ◽  
Practical Reality ◽  
Naca 0012

Supersonic flight has become a practical reality since the 1950s. One of the first ways to study high speed effects of the shock waves is to evaluate the aerodynamic coefficients of an airfoil. The work described herein refers to a series of 2.5D LES numeric simulations, to investigate the behavior of the shock wave on the airfoil. To reduce the unwanted effects, a porous surface is placed on 80% of suction and pressure side of a NACA 0012 airfoil. Solving the motion equations was carried out with Ansys Fluent. Qualitative comparison consists in the pressure contours visualization for different angles of attack, showing how shock waves form on the airfoil surfaces. After plotting the polar diagrams, CL=f(AoA) and CL=f(CD), a quantitative comparison was made between the baseline airfoil and the same airfoil but with porous media on each surface side.

A simple constitutive model for predicting the pressure histories developed behind rigid porous media impinged by shock waves

2013 ◽  
Vol 718 ◽  
pp. 507-523 ◽  
Author(s):  
O. Ram ◽  
O. Sadot
Keyword(s):  
Shock Wave ◽  
Porous Medium ◽  
Porous Media ◽  
Shock Waves ◽  
Constitutive Model ◽  
Wave Attenuation ◽  
Front Face ◽  
Viscous Effects ◽  
Pressure History ◽  
Target Wall

AbstractShock wave attenuation by means of rigid porous media is often applied when protective structures are dealt with. The passage of a shock wave through a layer of porous medium is accompanied by diffractions and viscous effects that attenuate and weaken the transmitted shock, thus reducing the load that develops on the target wall that is placed behind the protective layer. In the present study, the parameters governing the pressure build-up on the target wall are experimentally investigated using a shock tube facility. Different porous samples are impinged by normal shock waves of various strengths and the subsequent pressure histories that are developed on the target wall are recorded. In addition, different standoff distances from the target wall are investigated. Assuming that the flow through the porous medium is close to being isentropic enabled us to develop a general constitutive model for predicting the pressure history developed on the target wall. This model can be applied to predict the pressure build-up on the target wall for any pressure history that is imposed on the front face of the porous sample without the need to conduct numerous experiments. Results obtained by other investigators are found to be in very good agreement with the predictions of the presently developed constitutive model.

scholarly journals Bubbles with shock waves and ultrasound: a review

2015 ◽  
Vol 5 (5) ◽  
pp. 20150019 ◽  
Author(s):  
Siew-Wan Ohl ◽  
Evert Klaseboer ◽  
Boo Cheong Khoo
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
Biomedical Applications ◽  
High Speed ◽  
Experimental Studies ◽  
High Intensity Focused Ultrasound ◽  
High Speed Photography ◽  
Sound Waves ◽  
Bubble Cloud ◽  
Bubble Interaction

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed ‘acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics–bubble interactions, with a focus on shock wave–bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the ‘resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave–bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead.

scholarly journals Edge Detection and Machine Learning Approach to Identify Flow Structures on Schlieren and Shadowgraph Images

2020 ◽  
pp. paper15-1-paper15-14
Author(s):  
Irina Znamenskaya ◽  
Igor Doroshchenko ◽  
Daria Tatarenkova
Keyword(s):  
Machine Learning ◽  
Shock Wave ◽  
Shock Waves ◽  
Edge Detection ◽  
High Speed ◽  
Gas Flow ◽  
Flow Structures ◽  
Learning Approach ◽  
Wave Detection ◽  
Machine Learning Approach

Schlieren, shadowgraph and other types of refraction-based techniques have been often used to study gas flow structures. They can capture strong density gradients, such as shock waves. Shock wave detection is a very important task in analyzing unsteady gas flows. High-speed imaging systems, including high-speed cameras, are widely used to record large arrays of shadowgraph images. To process large datasets of the high-speed shadowgraph images and automatically detect shock waves, convective plumes and other gas flow structures, two computer software systems based on the edge detection and machine learning with convolutional neural networks (CNN) were developed. The edge-detection software utilizes image filtering, noise removing, background image subtraction in the frequency domain and edge detection based on the Canny algorithm. The machine learning software is based on CNN. We developed two neural networks working together. The first one classifies the image dataset and finds images with shock waves. The other CNN solves the regression task and defines shock wave position (single number) based on image pixels tensor (3-D array of numbers) for each image. The supervised learning code based on example input-output pairs was developed to train models. It was shown, that the machine learning approach gives better results in shock wave detection accuracy, especially for low-quality images with a strong noise level. Software system for automated shadowgraph images processing and x-t curves of the shock wave and convective plume movement plotting was developed.

scholarly journals SHOCKWAVE STUDY ON THE WINGS NACA 0012, NACA 64 - 206, AND NASA SC (2) - 0706 WITH Λ = 15O AT 0.85 MACH NUMBER

2021 ◽  
Vol 2 (1) ◽  
pp. 025-032
Author(s):  
Dewi Puspitasari ◽  
Kasyful Warist Kiat
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Cfd Simulation ◽  
Lower Surface ◽  
Aerodynamic Performance ◽  
Ansys Fluent ◽  
Aircraft Wings ◽  
Contour Plots ◽  
The Difference ◽  
Naca 0012

Airfoil is used as a basic form on aircraft wings. Airfoil on the wing of the aircraft is used to produce lift that will lift the fuselage into the air. Lifting force results from the difference in pressure between the upper surface and the lower surface of an aircraft wings. In high speed flights shockwave will occur at certain parts of the wing which will adversely affect the aerodynamic performance of the wing. Wing aerodynamic performance at high speeds can be improved in various ways, one of which is by giving a angle to the wing span called a swept angle. This study will use 3D CFD simulation methods using Ansys Fluent. The airfoil used are NACA 0012, NACA 64-206, and NASA SC (2) -0706 with a chord length of 1 m, AR = 5, and λ = 1 with backward swept angle Λ = 15 °. Free stream flow is air flowing with Mach Number = 0,85 at sea level and steady conditions. Based on the simulation results, shock occurs on the upper and lower surfaces for NACA 0012 with Cl = 0 due to symmetric airfoil, whereas shock occurs only on the upper surface for NACA 64-206 and NASA SC (2) - 0706 with a Cl / Cd value of 18.55 ( NACA 64-206) and 20.78 (NASA SC (2) - 0706). This simulation also provides a visual representation of Mach Number contour plots in the middle stretch (Midspan) of the wing and Cl and Cd data.

scholarly journals Numerical and experimental evaluation of shock dividers

Shock Waves ◽  
2022 ◽  
Author(s):  
M. Rezay Haghdoost ◽  
B. S. Thethy ◽  
M. Nadolski ◽  
B. Seo ◽  
C. O. Paschereit ◽  
...  
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
Numerical Simulations ◽  
Total Pressure ◽  
High Speed ◽  
Pressure Probe ◽  
Width Ratio ◽  
Pressure Pulsations ◽  
Pulse Detonation ◽  
Shock Dynamics

AbstractMitigation of pressure pulsations in the exhaust of a pulse detonation combustor is crucial for operation with a downstream turbine. For this purpose, a device termed the shock divider is designed and investigated. The intention of the divider is to split the leading shock wave into two weaker waves that propagate along separated ducts with different cross sections, allowing the shock waves to travel with different velocities along different paths. The separated shock waves redistribute the energy of the incident shock wave. The shock dynamics inside the divider are investigated using numerical simulations. A second-order dimensional split finite volume MUSCL-scheme is used to solve the compressible Euler equations. Furthermore, low-cost simulations are performed using geometrical shock dynamics to predict the shock wave propagation inside the divider. The numerical simulations are compared to high-speed schlieren images and time-resolved total pressure recording. For the latter, a high-frequency pressure probe is placed at the divider outlet, which is shown to resolve the transient total pressure during the shock passage. Moreover, the separation of the shock waves is investigated and found to grow as the divider duct width ratio increases. The numerical and experimental results allow for a better understanding of the dynamic evolution of the flow inside the divider and inform its capability to reduce the pressure pulsations at the exhaust of the pulse detonation combustor.

scholarly journals Observations of shock waves in cloud cavitation

1998 ◽  
Vol 355 ◽  
pp. 255-283 ◽  
Author(s):  
G. E. REISMAN ◽  
Y.-C. WANG ◽  
C. E. BRENNEN
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
High Speed ◽  
Leading Edge ◽  
Wave Structure ◽  
Cavitating Flows ◽  
Cloud Cavitation ◽  
Radiated Noise ◽  
Wave Dynamics ◽  
New Perspective

This paper describes an investigation of the dynamics and acoustics of cloud cavitation, the structures which are often formed by the periodic breakup and collapse of a sheet or vortex cavity. This form of cavitation frequently causes severe noise and damage, though the precise mechanism responsible for the enhancement of these adverse effects is not fully understood. In this paper, we investigate the large impulsive surface pressures generated by this type of cavitation and correlate these with the images from high-speed motion pictures. This reveals that several types of propagating structures (shock waves) are formed in a collapsing cloud and dictate the dynamics and acoustics of collapse. One type of shock wave structure is associated with the coherent collapse of a well-defined and separate cloud when it is convected into a region of higher pressure. This type of global structure causes the largest impulsive pressures and radiated noise. But two other types of structure, termed ‘crescent-shaped regions’ and ‘leading-edge structures’ occur during the less-coherent collapse of clouds. These local events are smaller and therefore produce less radiated noise but the interior pressure pulse magnitudes are almost as large as those produced by the global events.The ubiquity and severity of these propagating shock wave structures provides a new perspective on the mechanisms reponsible for noise and damage in cavitating flows involving clouds of bubbles. It would appear that shock wave dynamics rather than the collapse dynamics of single bubbles determine the damage and noise in many cavitating flows.

scholarly journals Development of Shock-Wave-Powered Actuators for High Speed Positioning (Second Report: Characteristics of Diaphragmless Shock Tube and Responsiveness of Actuator)

2013 ◽  
Vol 7 (5) ◽  
pp. 558-563
Author(s):  
Akira Kotani ◽  
◽  
Toshiharu Tanaka ◽  
Akira Hirano ◽  
Keyword(s):  
Shock Wave ◽  
High Pressure ◽  
Shock Waves ◽  
Shock Tube ◽  
High Speed ◽  
Industrial Robots ◽  
Piston Motion ◽  
Diaphragmless Shock Tube ◽  
High Responsiveness ◽  
Piston Speed

Shock tubes experiments are conducted on applications of shock waves to the actuator. The high-pressure and low-pressure sections of a general shock tube are separated by a diaphragm. In this study, a shock wave is generated by “diaphragmless shock tube” which is divided into two sections by a driver piston instead of the diaphragm. We have previously reported on the motion of a driven piston powered by a shock wave. However, not only piston speed but also high responsiveness is required for practical actuators used on manufacturing lines, in industrial robots, etc., The diaphragmless shock tube constructed in this paper is structured to be able to examine not only the motion of the driven piston but also the motion of the driver piston. In addition, the responsiveness of the piston motion of the actuator powered by shock waves is examined. It follows from what has been said thus far that a shock wave can be applied to an actuator with high responsiveness.

Multiple Shock Waves and its Unsteady Characteristics in Internal Flows

2019 ◽  
Author(s):  
Jintu K. James ◽  
Heuy Dong Kim
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
Flow Field ◽  
High Speed ◽  
Flow Characteristics ◽  
Wave Pattern ◽  
Time Resolved ◽  
Constant Area ◽  
Boundary Layer Interaction ◽  
Multiple Shock

Abstract Shock wave turbulent boundary layer interaction is a fundamental phenomenon observed in most of the gas dynamics applications such as wind tunnels, supersonic air intakes, transonic airfoil, nozzle flows, etc. The flow field and shock wave pattern in a constant area duct are analyzed experimentally. The focus of the present study is to present the time-resolved flow characteristics of the multiple shock waves and its oscillations. High-speed Schlieren flow visualization is used to capture the transient shock structure in the wind tunnel constant area test section. A gradient-based image processing was incorporated to capture the shock excursion details. Results indicate that the shock pattern is unsymmetrical in the flow field. The foot of the lambda shock wave in the upper and lower exhibit a difference in axial location and there is a large difference in this value at the mean position when the shock moves in the upstream direction compared to the downstream movement.

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