Optical Wall-Shear Probe With Micro-Lens Imaging for Near-Wall Resolution
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Solution Overview
Problem
Existing probes for measuring wall shear stress are inadequate for accurately characterizing the full spectrum of fluid flow regimes due to size limitations, spatial averaging, and bandwidth constraints, particularly in turbulent flows, and lack the resolution needed for laminar and transitional flows.
Innovation Solution
An optical probe with an imager, light guide, and micro-lens array that collects images to determine wall shear stress, using molecular tagging velocimetry, particle image velocimetry, or particle tracking velocimetry, and is compact enough to be recessed within a wall without interfering with fluid flow, allowing for high-resolution measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing probes are used to measure wall shear stress, then the measurement can be obtained, but the spatial resolution is insufficient due to probe size being larger than the viscous wall unit for turbulent flows
Solution Approach 1:
The patent replaces traditional mechanical contact-based wall shear stress probes with an optical measurement system. The optical probe uses light-based velocimetry techniques (such as particle image velocimetry or molecular tagging velocimetry) to measure near-wall velocity gradients without physical contact, enabling measurements at scales below the viscous wall unit while eliminating spatial averaging effects that plague mechanical probes
Solution Approach 2:
The patent transitions from direct wall-mounted mechanical sensing to optical measurement in the fluid domain near the wall. By measuring velocity gradients in the near-wall region through optical techniques rather than direct wall contact, the system achieves higher spatial resolution comparable to or smaller than the viscous wall unit scale
2Productivity
If existing probes are used to measure wall shear stress, then the measurement can be obtained, but the bandwidth is limited which restricts accurate characterization of laminar and transitional flows
Solution Approach 1:
The optical probe system is designed to universally measure wall shear stress across all flow regimes (laminar, transitional, and turbulent) using the same fundamental optical velocimetry technique. The system adjusts measurement parameters such as interrogation window size and sampling frequency according to the flow regime, enabling accurate characterization from low-speed laminar flows to high-speed turbulent flows without requiring regime-specific hardware
Solution Approach 2:
The patent employs dynamic measurement capabilities with adjustable temporal resolution to match the characteristic time scales of different flow regimes. For laminar flows with longer time scales, the system uses lower sampling rates, while for turbulent flows with shorter time scales (10 μs), the system increases sampling frequency and reduces interrogation window sizes to capture rapid velocity fluctuations
3Object-affected harmful factors
If a compact optical probe is used to be recessed within a wall, then the interference with fluid flow is minimized, but the optical path and imaging quality must be maintained
Solution Approach 1:
The patent nests the optical probe components within a recessed mounting structure in the wall. The objective lens, micro-lens array, and imager are arranged in a compact nested configuration that fits within the wall thickness, allowing the probe to be flush with or recessed into the wall surface without protruding into the flow domain, thereby minimizing flow interference while maintaining optical functionality
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The optical probe provides accurate characterization of wall shear stress across various fluid flow regimes by resolving near-wall velocity gradients and velocity fields, enabling precise measurements without disturbing the fluid flow.
Implementation Method 1
a light guide configured to steer light from a light source to the region of interest
Implementation Method 2
an objective configured to focus light reflected off of the region of interest
Implementation Method 3
an objective configured to focus light reflected off of the region of interest to the line of sight of the imager
Implementation Method 4
a micro-lens array at the objective. The micro-lens array is configured to focus light from the objective onto the imager
Data Source
AI summary
Aspects of this disclosure are directed to optical probes for collecting images of a region of interest for determining wall shear stress. The optical probe includes an imager with a line of sight and a light guide configured to steer light from a light source to the region of interest. The optical probe includes an objective configured to focus light reflected off of the region of interest to the line of sight of the imager. The optical probe can include a micro-lens array at the objective. The micro-lens array can focus light from the objective onto the imager. The imager can collect images from the light from the micro-lens array for determining wall shear stress at the region of interest.