scholarly journals Experimental study of particle concentration fluctuations in a turbulent steady flow

2008 ◽  
Vol 49 ◽  
pp. 121-126 ◽  
Author(s):  
François-Xavier Cierco ◽  
Mohamed Naaim ◽  
Florence Naaim-Bouvet
Keyword(s):  
Image Processing ◽  
Experimental Study ◽  
High Speed ◽  
Particle Concentration ◽  
Free Stream ◽  
Frequency Range ◽  
Wind Tunnel Experiments ◽  
Simple Theoretical Model ◽  
Over Time

AbstractSpecific features of the physics of blown sand and PVC particles were investigated in wind-tunnel experiments. The fluctuations in particle concentration over time were derived from image processing of high-speed films (500 Hz). Spectral analysis of these time series showed a slowly decreasing slope within a frequency range that could be larger than the inertial sub-range of the free stream. A specific transport regime also appears in the lower part of the flow for frequencies less than 10 Hz. The role of turbulence in the generation of this regime is discussed using a simple theoretical model able to describe the aerodynamic behavior of a particle.

Experimental Study of Kick up Phenomenon in Thermosonic Wire-Bonding

2012 ◽  
Vol 160 ◽  
pp. 77-81
Author(s):  
Jing Jing Tian ◽  
Lei Han
Keyword(s):  
Image Processing ◽  
Experimental Study ◽  
High Speed ◽  
Gold Wire ◽  
Wire Bonding ◽  
Processing Method ◽  
Experimental Results ◽  
High Speed Camera ◽  
Depth Study ◽  
Thermosonic Wire Bonding

Kick-up phenomenon during looping is an important factor in thermosonic wire bonding. In this study, the loping process during wire bonding was recorded by using high-speed camera, and wire profiles evolution was obtained from images sequence by image processing method. With a polynomial fitting, the wire loop profiling was described by the curvature changing, and kick-up phenomenon on gold wire was found between the instant of 290th frame(0.0537s) to 380th frame (0.0703s), the change of curvature is divided into three phases, a looping phase, a mutation phase and a kick-up phase. While in the kick-up phase, the kick up phenomenon is the most obvious. These experimental results were useful for in-depth study of kick-up phenomenon by simulation.

scholarly journals On active control of laminar–turbulent transition on two-dimensional wings

2011 ◽  
Vol 369 (1940) ◽  
pp. 1382-1395 ◽  
Author(s):  
Ralf Erdmann ◽  
Andreas Pätzold ◽  
Marcus Engert ◽  
Inken Peltzer ◽  
Wolfgang Nitsche
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Active Control ◽  
High Speed ◽  
Control Algorithm ◽  
Frequency Range ◽  
Wind Tunnel Experiments ◽  
Low Speed ◽  
Turbulent Transition ◽  
Mach Numbers

This paper gives an overview of drag reduction on aerofoils by means of active control of Tollmien–Schlichting (TS) waves. Wind-tunnel experiments at Mach numbers of up to M x =0.42 and model Reynolds numbers of up to Re c =2×10 6 , as well as in-flight experiments on a wing glove at Mach numbers of M <0.1 and at a Reynolds number of Re c =2.4×10 6 , are presented. Surface hot wires were used to detect the linearly growing TS waves in the transitional boundary layer. Different types of voice-coil- and piezo-driven membrane actuators, as well as active-wall actuators, located between the reference and error sensors, were demonstrated to be effective in introducing counter-waves into the boundary layer to cancel the travelling TS waves. A control algorithm based on the filtered- x least mean square (FxLMS) approach was employed for in-flight and high-speed wind-tunnel experiments. A model-predictive control algorithm was tested in low-speed experiments on an active-wall actuator system. For the in-flight experiments, a reduction of up to 12 dB (75% TS amplitude) was accomplished in the TS frequency range between 200 and 600 Hz. A significant reduction of up to 20 dB (90% TS amplitude) in the flow disturbance amplitude was achieved in high-speed wind-tunnel experiments in the fundamental TS frequency range between 3 and 8 kHz. A downstream shift of the laminar–turbulent transition of up to seven TS wavelengths is presented. The cascaded sensor–actuator arrangement given by Sturzebecher & Nitsche in 2003 for low-speed wind-tunnel experiments was able to shift the transition Δ x =240 mm (18%  x / c ) downstream by a TS amplitude reduction of 96 per cent (30 dB). By using an active-wall actuator, which is much shorter than the cascaded system, a transition delay of seven TS wavelengths (16 dB TS amplitude reduction) was reached.

scholarly journals Effect of Strut Geometry in Supersonic Mixing

2020 ◽  
Vol 9 (6) ◽  
pp. 386-389
Keyword(s):  
Experimental Study ◽  
Mach Number ◽  
Residence Time ◽  
High Speed ◽  
Free Stream ◽  
Mixing Enhancement ◽  
Supersonic Mixing ◽  
Mixing Chamber ◽  
Mixing Method ◽  
Selection Of

Effective mixing in a short mixing chamber is a major challenge in supersonic air breathing engines, especially the mixing between two high speed co-axial streams. The residence time is a major factor to get the two streams properly mixed. The selection of mixing method is crucial in the supersonic conditions. An experimental study has been performed on the supersonic mixing of air from strut injectors of various combinations in their trailing ramp angles with a free stream air of Mach number 2. Two different configurations of geometries, a plain geometry and a lobed geometry considered and further two different combinations, slot and hole injections, are taken for the study in each geometry. Among different combinations, it is found that a better mixing enhancement is achieved for the 9o lobed geometry struts.

When Being Discrepant from One's Ideal or Ought Selves Hurts: The Moderating Role of Neuroticism

2013 ◽  
Vol 27 (3) ◽  
pp. 256-270 ◽  
Author(s):  
Ryan Y. Hong ◽  
Widyasari Triyono ◽  
Pearlyn S. Ong
Keyword(s):  
Experimental Study ◽  
Possible Selves ◽  
Depression And Anxiety ◽  
Partial Support ◽  
Discrepancy Theory ◽  
Mediating Mechanisms ◽  
Self Discrepancy ◽  
Moderating Role ◽  
Over Time

Self–discrepancy theory posits that people experience emotional consequences when they perceive discrepancies between their actual and possible selves. However, the extent to which people react emotionally to these self–discrepancies (i.e. ideal, ought and undesired) may be a function of individual differences in neuroticism. Across both experimental (Study 1; N = 155) and correlational designs (Study 2; N = 139) involving college students, the authors demonstrated that neuroticism moderated the discrepancy–emotion associations such that high–neuroticism individuals showed elevated depression and anxiety symptoms when their self–discrepancies were activated. The heightened symptoms were maintained over time. Negative repetitive thoughts (i.e. rumination and worry) were examined as potential mediating mechanisms between the discrepancy × neuroticism interaction and symptoms. Partial support was obtained in that rumination mediated between undesired discrepancy × neuroticism interaction and anxious/depressive symptoms. Implications and possible theoretical extensions for self–discrepancy theory are discussed. Copyright © 2012 John Wiley & Sons, Ltd.

Towards simulating natural transition in hypersonic boundary layers via random inflow disturbances

2018 ◽  
Vol 847 ◽  
Author(s):  
Christoph Hader ◽  
Hermann F. Fasel
Keyword(s):  
Boundary Layers ◽  
High Speed ◽  
Free Stream ◽  
Wind Tunnel Experiments ◽  
Hypersonic Boundary Layers ◽  
Random Forcing ◽  
Turbulent Transition ◽  
Breakdown Mechanism ◽  
Wide Range ◽  
Selection Of

A random forcing approach was implemented into a high-order accurate finite-difference code in order to investigate ‘natural’ laminar–turbulent transition in hypersonic boundary layers. In hypersonic transition wind-tunnel experiments, transition is caused ‘naturally’, by free-stream disturbances even when so-called quiet tunnels are employed such as the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University. The nature and composition of the free-stream disturbance environment in high-speed transition experiments is difficult to assess and therefore largely unknown. Consequently, in the direct numerical simulations (DNS) presented here, the free-stream disturbance environment is simply modelled by random pressure (acoustic) disturbances with a broad spectrum of frequencies and a wide range of azimuthal wavenumbers. Results of a high-resolution DNS for a flared cone at Mach 6, using the random forcing approach, are presented and compared to a fundamental breakdown simulation using a ‘controlled’ disturbance input (with a specified frequency and azimuthal wavenumber). The DNS results with random forcing clearly exhibit the ‘primary’ and ‘secondary’ streak pattern, which has previously been observed in our ‘controlled’ breakdown simulations and the experiments in the BAM6QT. In particular, the spanwise spacing of the ‘primary’ streaks for the random forcing case is identical to the spacing obtained from the ‘controlled’ fundamental breakdown simulation. A comparison of the wall pressure disturbance signals between the random forcing DNS and experimental data shows remarkable agreement. The random forcing approach seems to be a promising strategy to investigate nonlinear breakdown in hypersonic boundary layers without introducing any bias towards a distinct nonlinear breakdown mechanism and/or the selection of specific frequencies or wavenumbers that is required in the ‘controlled’ breakdown simulations.

A Statistical Study of Process Variables to Optimize a High Speed Curtain Coater: Part I

TAPPI Journal ◽  
2009 ◽  
Vol 8 (1) ◽  
pp. 20-26 ◽  
Author(s):  
PEEYUSH TRIPATHI ◽  
MARGARET JOYCE ◽  
PAUL D. FLEMING ◽  
MASAHIRO SUGIHARA
Keyword(s):  
Boundary Layer ◽  
Experimental Design ◽  
High Speed ◽  
Statistical Study ◽  
Process Variables ◽  
High Speeds ◽  
The Stability ◽  
Air Removal ◽  
Removal System

Using an experimental design approach, researchers altered process parameters and material prop-erties to stabilize the curtain of a pilot curtain coater at high speeds. Part I of this paper identifies the four significant variables that influence curtain stability. The boundary layer air removal system was critical to the stability of the curtain and base sheet roughness was found to be very important. A shear thinning coating rheology and higher curtain heights improved the curtain stability at high speeds. The sizing of the base sheet affected coverage and cur-tain stability because of its effect on base sheet wettability. The role of surfactant was inconclusive. Part II of this paper will report on further optimization of curtain stability with these four variables using a D-optimal partial-facto-rial design.

HIGH-SPEED OBSERVATIONS OF HIGHLY EROSIVE VORTEX CAVITATION USING IMAGE PROCESSING

1995 ◽  
Vol 2 (2) ◽  
pp. 161-172 ◽  
Author(s):  
Kohtaro Ohba ◽  
Hitoshi Soyama ◽  
Sho Takeda ◽  
Hikaru Inooka ◽  
Risaburo Oba
Keyword(s):  
Image Processing ◽  
High Speed
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