banner image
No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
Channelling optics for high quality imaging of sensory hair
Rent this article for


Image of FIG. 1.
FIG. 1.

Optics of the channelling LDM (height not to scale).

Image of FIG. 2.
FIG. 2.

Lens array and aperture plate.

Image of FIG. 3.
FIG. 3.

Channelling LDM applied to a text block (object), showing magnified regions of interest (image on camera chip).

Image of FIG. 4.
FIG. 4.

Ray hitting meniscus non-parallel to surface normal.

Image of FIG. 5.
FIG. 5.

Lens array geometry.

Image of FIG. 6.
FIG. 6.

Comparison of rms aberration of singlet and doublet lens at different magnification.

Image of FIG. 7.
FIG. 7.

Subsection of the 30 × 30 micro-pillar field as seen by a standard microscope. The image demonstrates good quality and homogeneity of the cylindrical structures.

Image of FIG. 8.
FIG. 8.

Wall jet generator and flow visualization system. The light sheet and camera position is shown in orientation for the PIV-measurements.

Image of FIG. 9.
FIG. 9.

Smoke visualization of the wall jet. View from top onto the wall. The location of observed micro-pillars is indicated by a square in the bottommost image.

Image of FIG. 10.
FIG. 10.

Ensemble average of the cross-sectional velocity field downstream of the nozzle, measured by classical PIV. The jet Reynolds number is 1290. The profiles show the development of the wall jet in the transitional region.

Image of FIG. 11.
FIG. 11.

Image sequence showing one period of the quasi-periodic roll-up of larger vortical structures. The dashed line indicates the reference location, where the first picture of the sequence shows the same position of the roller structure as the last one. The five vertical, white bars in the uppermost image indicate the position of the micro-pillars. Each bar corresponds to one micro-pillar. The height of the bars is enlarged about four times, whereas their lateral distance scales correctly.

Image of FIG. 12.
FIG. 12.

Calibration curve showing the normalized micro-pillar-tip deflection at different wall shear stress in the lower limit of load range. Calibration is carried out in a Couette flow apparatus generating a constant velocity gradient within the flow channel. +calibration data; ■micro-pillar side view; –fit of calibration data to equation w/[μm] = exp (τ/[Pa] + 2.6099) − 13.597.

Image of FIG. 13.
FIG. 13.

Visualization of the flow structure in the wake of a wall-bounded cylinder with a free end at pillar Reynolds number Re = 33. The flow is from left to right. The illuminated plane is centered with the incoming flow direction and the pillar axis.

Image of FIG. 14.
FIG. 14.

Setup for dynamic calibration. The micro-pillar field is located directly between two speakers, observed by the channelling LDM.

Image of FIG. 15.
FIG. 15.

Maximum velocity of the speaker cone as a function of the speaker frequency.

Image of FIG. 16.
FIG. 16.

Sensitivity of the micro-pillar field as a function of the frequency of the oscillating flow.

Image of FIG. 17.
FIG. 17.

Setup for wall shear stress measurements in a wall jet by means of channelling LDM.

Image of FIG. 18.
FIG. 18.

Images of the micro-pillar array at rest (top) and with arbitrary deflection at (bottom). The flow direction is from left to right.

Image of FIG. 19.
FIG. 19.

(a) mean wall shear stress in streamwise direction , (b) mean friction coefficient C f for different Reynolds number of wall jet. The location of the micro-pillar field is at 1 < x/d < 1.2.

Image of FIG. 20.
FIG. 20.

Probability density functions (PDF) of streamwise wall shear stress fluctuations τ u for different Reynolds numbers of the wall jet. The location of the micro-pillar field is at 1 < x/d < 1.2.

Image of FIG. 21.
FIG. 21.

PDF of at Re = 2360, fitted by a skewed Gaussian profile.

Image of FIG. 22.
FIG. 22.

Spectrum of wall shear stress fluctuations in the transitional wall jet at 1 < x/d < 1.2. The frequency of the shear layer roll-up f = 625 Hz and its doubling are highlighted.

Image of FIG. 23.
FIG. 23.

Mean deflection and arbitrary snapshot fluctuation of micro-pillars in the transitional wall jet at and 1 < x/d < 1.2. The direction of the flow is from left to right.

Image of FIG. 24.
FIG. 24.

Time series of the first three POD coefficients at and 1 < x/d < 1.2.

Image of FIG. 25.
FIG. 25.

High energetic POD modes ϕ1, ϕ2, ϕ3 of wall shear stress fluctuations obtained by measuring the fluid-imposed deflections of twenty-one micro-pillars at and 1 < x/d < 1.2. The direction of the flow is from left to right. The contribution to the total energy is given in percent above the vector field.


Generic image for table
Table I.

Lenses of the channelling LDM.


Article metrics loading...


Full text loading...

This is a required field
Please enter a valid email address
752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Channelling optics for high quality imaging of sensory hair