Rotating Disk Test Fixture for Anisotropic Skin Friction
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Solution Overview
Problem
Existing methods for measuring the skin friction coefficient of anisotropic surface finishes are cumbersome, requiring fragile and difficult-to-calibrate instrumentation that often needs customization for each test, making it challenging to accurately determine the skin friction coefficient as a function of flow direction.
Innovation Solution
A test fixture with a rotating circular specimen disk and pressure rakes positioned upstream and downstream to measure total pressures, along with static pressure taps on a plate, allows for the determination of skin friction coefficients as a function of flow angle, enabling the characterization of anisotropic surface finishes in a fluid tunnel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional instrumentation is used to measure skin friction coefficient, then measurement capability is achieved, but the instrumentation becomes fragile and difficult to calibrate
Solution Approach 1:
The patent replaces traditional mechanical skin friction measurement instrumentation with a pressure-based measurement system. Pressure rakes with multiple pressure ports measure pressure distribution across the boundary layer, and static pressure taps measure wall pressure. This substitution eliminates fragile mechanical shear stress sensors while achieving accurate skin friction coefficient determination through pressure differential measurements and boundary layer analysis.
2Adaptability or versatility
If customized test fixtures are used for particular measurements, then measurement specificity is improved, but device complexity and setup time increase
Solution Approach 1:
The patent employs a universal test fixture design where the plate with cavity, pressure rakes, and static pressure taps can measure skin friction coefficients for various surface finishes (smooth, rough, anisotropic) under different flow conditions. The motor assembly enabling rotation of specimens and the interchangeable specimen disks provide multi-functionality without requiring custom fixtures for each measurement type, reducing overall device complexity while maintaining adaptability.
3Measurement precision
If traditional measurement methods are used, then initial setup is achieved, but frequent recalibration is required during testing
Solution Approach 1:
The pressure-based measurement system with multiple pressure ports and static pressure taps provides inherent reference points and distributed measurements that self-validate during testing. The system continuously monitors pressure distribution across the boundary layer and wall pressure, enabling real-time verification of measurement consistency without requiring external recalibration procedures, thus eliminating time loss associated with frequent recalibration.
4Ease of operation
If anisotropic surface finishes are tested with fixed flow direction, then measurement simplicity is maintained, but flow direction effects are not captured
Solution Approach 1:
The patent incorporates a motor assembly that dynamically rotates the specimen disk to various angles relative to the flow direction, enabling measurement of skin friction coefficients for anisotropic surface finishes at multiple flow angles. This dynamic adjustment capability captures the flow direction dependency of anisotropic surfaces while maintaining operational simplicity through automated rotation control, preventing loss of critical angular dependency information.
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
This solution provides a robust and efficient method for measuring skin friction coefficients, accounting for flow direction effects and reducing the need for frequent instrumentation recalibration, thereby improving the accuracy and repeatability of skin friction measurements.
Implementation Method 1
a first pressure rake, coupled to the plate, positioned upstream of the circular specimen disk, configured to measure first total pressures throughout a height of an upstream boundary layer; a second pressure rake, coupled to the plate, positioned downstream of the circular specimen disk, configured to measure second total pressures throughout a height of a downstream boundary layer
Implementation Method 2
a plurality of static pressure taps in a top surface of the plate for measuring static pressures on the top surface of the plate
Implementation Method 3
a motor assembly, coupled to plate, configured to rotate the circular specimen disk through a plurality of angles relative to a direction of the fluid flow during operation of the test fixture
Implementation Method 4
During operation of the test fixture in the fluid tunnel, a fluid can flow over the plate in a particular direction
Data Source
AI summary
A test fixture for measuring the skin friction of anisotropic surface finish on a material is described. The test fixture can be utilized in a wind tunnel. The test fixture can include a plate having a cavity configured to receive a circular specimen disk. A motor can be coupled to the plate to rotate the circular specimen disk. During a test, a fluid can flow over the plate in a particular direction and the motor can rotate the circular specimen disk to determine the effect of the flow angle on the average skin friction coefficient of a surface finish of a material. The circular specimen disk can easily be attached and detached from the test fixture to allow circular specimen disks with different surface finishes to be tested.