The role of surface roughness in boundary layers continues to be a topic significant interest, especially with regard how controlled might used delay laminar-to-turbulent transition. Although it may useful for control, large-amplitude itself lead In an effort understand the breakdown mechanics associated roughness, experiments are conducted investigate steady and unsteady disturbances generated by three-dimensional elements whose amplitudes close critical roughness-based Reynolds number Re k...

Recent experiments on transient disturbance growth in boundary layers indicate that disturbances generated by surface roughness undergo suboptimal growth. The implication is the receptivity mechanism governing distribution of energy among continuous spectrum damped Orr–Sommerfeld/Squire modes produces distributions are significantly different from theoretical optimum. Experiments presented here intended to investigate how amplitude and diameter cylindrical elements arranged a spanwise array...

Receptivity of transient disturbances to surface roughness is a complicated phenomenon that governs both initial disturbance amplitudes and features the disturbances’ growth decay throughout boundary layer. The experiments described here use hotwire measurements in Blasius layer obtain detailed information on generated by spanwise-periodic array elements follows disturbances. results indicate energy associated with roughness-induced scales roughness-based Reynolds number, Rek, for values as...

Abstract Micro-convection caused by ponderomotive forces of the self-magnetic field a magnetic fluid in Hele-Shaw cell under action vertical homogeneous is studied both experimentally and numerically. It shown that non-potential force at Rayleigh numbers greater than critical value causes fingering interface between miscible non-magnetic fluids. The threshold number depends on smearing Fingering with its subsequent decay due to diffusion particles significantly increases mixing interface....

Highly monodispersed emulsions can be produced in microfluidic flow-focusing junctions (Anna et al 2003 Appl. Phys. Lett. 82 364–6, Baroud 2010 Lab Chip 10 2032–45). This is the reason why many industrial processes medical industry among others are based on droplet manipulation and involve at some point a step of dripping within junction. However, only few studies have focused flow field inside outside droplet, even though it necessary for understanding physical mechanism involved modeling...

Two experiments are conducted to investigate transient growth and bypass transition in boundary layers with moderate- high-amplitude roughness arrays. Unsteady multicomponent velocity measurements obtained a flat plate l ayer downstream of spanwise array cylindrical elements Reynolds numbers Rek = 202, 264 334. Measurements the unsteady streamwise velocities wake indicate that 720 Hz fluctuation leads rapidly at The Strouhal number this fluctuation, St 0.17, is good agreement previous...

Particle image velocimetry (PIV) often employs the cross-correlation function to identify average particle displacement in an interrogation window. The quality of correlation peak has a strong dependence on signal-to-noise ratio (SNR), or contrast images. In fact, variable-contrast images are not uncommon PIV community: Strong light sheet intensity variations, wall reflections, multiple scattering densely-seeded regions and two-phase flow applications likely sources local variations. this...

Transient growth of linearly stable disturbances is believed to play an important role in the subcritical transition laminar boundary layers and self-sustained nature layer fluctuations a fully turbulent flow. Prior work on transient has focused identifying optimum initial that result maximum growth. This paper addresses companion issue receptivity those disturbances, mechanism determines actual magnitudes are realized given physical situation. A synergistic combination experimental,...

This paper aims to quantify the Particle Image Velocimetry (PIV) measurement accuracy improvement along phase boundaries of two-phase flows, due use phase-separated PIV analysis, compared conventional analysis without separating phases. To compute true error produced by a patchwork synthetic image pair with known displacement is used (ground truth). As real flows might have arbitrary flow direction and magnitude across boundary, image-pair includes variety combinations, i.e. running into...

Abstract Obtaining pressure force for freely swimming microorganisms is a challenging yet important problem. Here, we report the kinematics and dynamics of zooplankton Acartia tonsa nauplius investigated using Micro Particle Image Velocimetry ( µ PIV). Using rigid object tracking, obtain sub-pixel accurate localization A. , revealing its highly periodic locomotion. We exploit this periodicity to phase-locked averaged position, speed, acceleration. The speed profile has distinct double peak,...

Constant temperature anemometry (CTA) is still the preferred method in measurement of key quantities turbulence investigations. One main challenges CTA finite length sensor often being larger than smallest eddies present flow, which leads to spatial averaging along sensor. The effect an under-estimated fluctuation intensity value, biased estimation heat- and mass- transfer characteristics flow value needs be corrected. There have been numerous correction schemes that aim estimate "true"...

The spatial resolution of Constant Temperature Anemometry (CTA) measurements is limited by the length (l) sensor, due to averaging smaller turbulent eddies over sensor (spatial filtering). There are several limitations and challenges connecting dimensions measurements, which explained in detail Ref. [1] Section 5.2. One limitation l/d ratio, should be kept above 200 minimize end conduction effects. This indirectly puts a on diameter (d) means minimizing also reduction its diameter. As side...

The spatial resolution of Constant Temperature Anemometry (CTA) measurements is limited by the length (l) sensor, due to averaging smaller turbulent eddies over sensor (spatial filtering). There are several limitations and challenges connecting dimensions measurements, which explained in detail Ref. [1] Section 5.2. One limitation l/d ratio, should be kept above 200 minimize end conduction effects. This indirectly puts a on diameter (d) means minimizing also reduction its diameter. As side...

Constant temperature anemometry (CTA) is still the preferred method in measurement of key quantities turbulence investigations. One main challenges CTA finite length sensor often being larger than smallest eddies present flow, which leads to spatial averaging along sensor. The effect an under-estimated fluctuation intensity value, biased estimation heat- and mass- transfer characteristics flow value needs be corrected. There have been numerous correction schemes that aim estimate "true"...