Test fixture to measure the average skin friction of anisotropic surfaces

Patent metadata

Field	Value
Publication number	US-10775265-B2
Application number	US-201816049714-A
Country	US
Kind code	B2
Filing date	Jul 30, 2018
Priority date	May 22, 2018
Publication date	Sep 15, 2020
Grant date	Sep 15, 2020

Abstract

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.

First claim

What is claimed is:

1. A test fixture for measuring skin friction of a surface finish on a material comprising:
a plate including a circular cavity configured to receive a circular specimen disk having the surface finish wherein the surface finish is aligned with a top surface of the plate when the circular specimen disk is placed in the circular cavity and wherein during operation of the test fixture a fluid flows over the plate and the circular specimen disk;
a motor assembly, coupled to plate, configured to rotate the circular specimen disk through a plurality of angles relative to a direction of a fluid flow during operation of the test fixture;
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; and
a plurality of static pressure taps in a top surface of the plate for measuring static pressures on the top surface of the plate wherein the first total pressures, the second total pressures and the static pressures are used to determine the skin friction of the surface finish as a function of the plurality of angles.

2. The test fixture of claim 1 wherein the first pressure rake includes a plurality of pressure probes each extending from a body of the first pressure rake, each arranged along a line perpendicular to the top surface of the plate and each substantially parallel to the top surface of the plate.

3. The test fixture of claim 2 , wherein tips of the plurality of the pressure probes are aligned with a point on the circular specimen disk which is most upstream in a flow of the fluid over the circular specimen disk.

4. The test fixture of claim 1 wherein the second pressure rake includes a plurality of pressure probes each extending from a body of the second pressure rake, each arranged along a line perpendicular to the top surface of the plate and each substantially parallel to the top surface of the plate wherein tips of the pressure probes are aligned with a point on the circular specimen disk which is most downstream in a flow of the fluid over the circular specimen disk.

5. The test fixture of claim 1 wherein a portion of the plurality of static pressure taps is arranged in a spanwise line across the plate upstream of the circular specimen disk.

6. The test fixture of claim 1 wherein a portion of the plurality of static pressure taps is arranged in a streamwise line along the plate extending from upstream of the circular specimen disk to downstream of the circular specimen disk.

7. The test fixture of claim 1 , further comprising a communication interface configured to receive command signals for the motor assembly, wherein the command signals are used to command the motor assembly to rotate the circular specimen disk during the operation of the test fixture.

8. The test fixture of claim 1 , further comprising a plurality of supports for raising the test fixture above a floor of a test section of a fluid tunnel.

9. The test fixture of claim 8 , further comprising one or more fairings designed to cover components extending from a bottom of the plate wherein the one or more fairings are shaped to reduce flow disturbances resulting from the fluid flowing over the fairings.

10. The test fixture of claim 1 , wherein a body of the first pressure rake or a body of the second pressure rake is shaped to reduce downstream flow disturbances resulting from the fluid flowing around the body.

11. The test fixture of claim 1 , wherein the plate includes a leading edge and a trailing edge and wherein the trailing edge includes attachment points for receiving a trailing edge control surface.

12. The test fixture of claim 1 , wherein, to reduce downstream flow disturbances, the plate includes a leading edge and a trailing edge, and wherein the leading edge is shaped to gradually transition from a finite radius of curvature associated with the leading edge to an infinite radius of curvature associated with the top surface of the plate, which is planar.

13. A material testing system comprising:
a fluid tunnel including a test section, a fluid driver system for driving a fluid through the test section and a control system for controlling the fluid driver system;
a test fixture, positioned in the test section, for measuring skin friction of a surface finish on a material including;
a plate including a circular cavity configured to receive a circular specimen disk having the surface finish wherein the surface finish is aligned with a top surface of the plate when the circular specimen disk is placed in the circular cavity and wherein, during operation of the test fixture the fluid flows over at least the top surface of the plate and the circular specimen disk;
a motor assembly, coupled to plate, configured to rotate the circular specimen disk through a plurality of angles relative to a direction of a fluid flow during operation of the test fixture;
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; and
a plurality of static pressure taps in the top surface of the plate for measuring static pressures on the top surface of the plate wherein the first total pressures, the second total pressures and the static pressures are used to determine the skin friction of the surface finish as a function of the plurality of angles.

14. The material testing system of claim 13 , wherein the plate is mounted in the test section such that the top surface of the plate is flush with a bottom surface of the test section.

15. The material testing system of claim 14 , further comprising a suction mechanism installed in the bottom surface of the test section, upstream of the plate, to eliminate and remove an effect of a boundary layer upstream of the plate.

16. The material testing system of claim 13 , further comprising supports configured to raise the plate above a bottom surface of the test section to allow the fluid to flow over the top surface of the plate and a bottom surface of the plate.

17. The material testing system of claim 16 , wherein gaps between spanwise edges of the plate and side walls of the test section are sealed to minimize a leakage of fluid between the top surface of the plate and the bottom surface of the plate.

18. The material testing system of claim 13 , wherein the control system is configured to control the fluid driver system to maintain an approximately constant unit Reynolds number during the operation of the test fixture.

19. The material testing system of claim 13 , wherein the control system is configured to control the motor assembly to rotate the circular specimen disk through the plurality of angles during the operation of the test fixture.

20. A method of determining skin friction of an anisotropic surface finish on a material comprising:
controlling a fluid tunnel to establish fluid flow over a test fixture wherein the test fixture includes a circular specimen disk and is positioned within a test section of the fluid tunnel;
measuring first total

Assignees

• Boeing Co

Inventors

• Dowgwillo Robert M
• Wiggins Jay
• Rafferty Bradley
• Brzozowski Daniel P

Classifications

• G01N19/00

  Investigating materials by mechanical methods (G01N3/00 - G01N17/00 take precedence) · CPC title

• G01M9/04

  Details · CPC title

• G01N3/04

  Chucks · CPC title

• G01M9/062 Primary

  Wind tunnel balances; Holding devices combined with measuring arrangements · CPC title

• G01N2203/0282

  Two dimensional, e.g. tapes, webs, sheets, strips, disks or membranes · CPC title