Wall Shear Sensor Split-Beam Flexure Pressure Gradient Error
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Solution Overview
Problem
Conventional wall shear sensors are unreliable in measuring wall shear stress in complex flow environments due to decreased accuracy caused by pressure gradients and shock waves, which existing indirect methods fail to address effectively.
Innovation Solution
A wall shear sensor with a floating element and a split-beam or multiple beam flexure, coupled with strain gauges, that sways perpendicular to the applied wall shear, allowing for direct measurement while minimizing errors from pressure gradients through a channel design that concentrates strain on specific portions of the flexure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional wall shear sensors are used to directly measure wall shear stress, then measurement sensitivity is improved, but measurement reliability deteriorates due to errors from pressure gradients and shock waves
Solution Approach 1:
The sensor head is divided into multiple independent sensing elements (first and second sensing elements) that measure wall shear stress in different directions. This segmentation allows the sensor to capture complex flow information while reducing the impact of pressure gradient errors through differential measurement techniques.
Solution Approach 2:
Each sensing element is designed with specific local characteristics optimized for its measurement function. The sensing elements have different orientations and configurations that make them sensitive to different components of wall shear stress, allowing the system to achieve high measurement precision while compensating for pressure gradient effects through the unique response of each element.
2Reliability
If indirect methods are used to infer wall shear stress, then reliability is improved in well-understood flows, but measurement precision deteriorates in complex flowfields
Solution Approach 1:
The patent replaces indirect inference methods with direct mechanical measurement using strain gauges bonded to the sensing elements. This substitution of measurement principle provides reliable and accurate data in complex flowfields by directly measuring the tangential frictional forces without requiring analytical correlations or assumptions about flow conditions.
3Device complexity
If single-beam flexure is used in wall shear sensor, then device complexity is reduced, but measurement precision deteriorates due to moment errors from pressure gradients
Solution Approach 1:
The single-beam flexure is segmented into multiple independent sensing elements that can measure wall shear stress in different directions. This segmentation maintains relative structural simplicity while improving measurement precision by enabling differential measurements that cancel out moment errors caused by pressure gradients and shock waves.
Solution Approach 2:
The sensing elements are positioned and oriented asymmetrically on the flexure to optimize their sensitivity to different components of wall shear stress. This asymmetric configuration allows the sensor to achieve high measurement accuracy while maintaining a simple single-beam structure, as the asymmetric positioning enables differential measurement capabilities without requiring multiple symmetric beams.
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 solution provides highly sensitive and accurate direct measurements of wall shear stress, significantly reducing errors from pressure gradients and shock waves, enhancing the reliability of wall shear measurements in complex flow conditions.
Implementation Method 1
at least one strain gauge coupled to the split-beam flexure. The strain gauge measures a strain imposed on a portion of the split-beam flexure when a wall shear is applied across a head surface of the sensing head
Implementation Method 2
The floating element has a sensing head opposite the base, and a split-beam or multiple beam flexure between the sensing head and the base. The floating element sways in a sway direction perpendicular to the first transverse axis of the floating element when wall shear is applied across the head surface of the sensing head
Data Source
AI summary
A wall shear sensor includes a floating element fixedly attached to a base. The floating element has a sensing head opposite the base, and a split-beam flexure between the sensing head and the base. The wall shear sensor further includes at least one strain gauge coupled to the split-beam flexure, which measures strain imposed on walls of the split-beam flexure when a wall shear is applied across a head surface of the sensing head. The split-beam flexure has at least one channel defined through the split-beam flexure perpendicular to a first transverse axis of the floating element. The floating element sways parallel to the first transverse axis of the floating element when the wall shear is applied. Wall shear measurement systems include a test body, a sensor housing mounted to the test body, and a wall shear sensor in the sensor housing.