A Guide to Wall Shear Stress Measurement – #11 – Summary & References

by | Aug 12, 2020 | A Guide to Wall Shear Stress Measurement, Tech News

This is the eleventh and final section in this blog post series, “A Guide to Wall Shear Stress Measurement,” and it provides a summary of the previous ten sections along with a comprehensive list of references used throughout the series. This guide first introduced itself, covered indirect vs. direct methods for measuring wall shear stress, then surveyed the various options for direct transduction, and lastly addressed sensor construction.

In sections 2 and 3, a number of measurement approaches were discussed including indirect techniques (e.g., surface/flow obstacles, heat transfer, and velocity profile methods) and direct techniques (e.g., film-based methods and floating-element sensors).

In sections 4, 5, 6, 7, and 8, floating element sensors were studied in more detail, addressing four main types of transduction (piezoresistivepiezoelectriccapacitive, and optical) and how to select the most appropriate type for a particular application.

Sections 9 and 10 then discussed the two main types of sensor construction (conventional fabrication and micromachining) and how to choose between them to best meet application requirements.

This series is intended to serve as an introductory guide to selecting a wall shear stress measurement tool. The papers listed in the References section provide significantly more detailed information about one or more of these techniques. For an in-depth technical review of shear stress measurement methods, see Naughton and Sheplak [13] or for more focused coverage of MEMS shear-stress sensors, see Sheplak et al. [14]. 

The table below summarizes some of the more significant attributes, strengths, and limitations of the various sensing techniques that were reviewed.

Sensing Technique


  • Measurement Method
  • Direct or Indirect
  • Mean or Fluctuating



Flow Obstacles

  • Fence
  • Micropillar
  • Preston or Stanton tubes
  • Pressure drop
  • Indirect (need correlation of pressure gradient or velocity to wall shear stress)
  • Mean
  • Ease of implementation
  • Poor bandwidth
  • Poor spatial resolution
  • May be qualitative data only
  • Physical flow perturbation

Heat Transfer

  • Hot wires
  • Hot films
  • Thermal shear-stress
  • Correlation between heat transfer and wall shear stress
  • Indirect (typically unknown correlation)
  • Mean and fluctuating
  • Physically non-intrusive
  • Lack of unique calibration
  • Frequency dependent heat transfer
  • Temperature drift
  • Flow perturbation from heat

Velocity profile

  • LDV
  • PIV
  • Doppler shift or image/particle tracking
  • Indirect
  • Mean (PIV provides limited bandwidth fluctuating data)
  • Physically non-intrusive
  • Flow seeing required
  • Low data rate due to poor seed density
  • Fabrication challenge – probe volumes not contained in viscous sublayer

Stress Sensitive Film

  • Oil-film
  • Liquid crystal
  • Optical imaging on film surface
  • Direct
  • Mean and fluctuating
  • Physically non-intrusive (although still imparts a flow perturbation due to heat transfer)
  • High cross coupling in shear and pressure deformation
  • External and bulky optics
  • Complex for real time measurement.

Floating Element Sensors

  • Capacitive
  • Piezo-resistive
  • Optical
  • Floating element transducer
  • Direct
  • Mean and fluctuating
  • Physically non-intrusive
  • Small, precise features with tight tolerances
  • Higher performance
  • Lower uncertainty and variance between sensors
  • Higher spatial resolution and higher bandwidth
  • Challenging to package
  • Need air/watertight covering to protect from flow
  • Contaminants

Thank you for reading “A Guide to Wall Shear Stress Measurement” and please comment below or contact us at info@thinkic2.com if you have any questions!

Table of Contents

  1. Overview
  2. Comparing Techniques – Indirect Measurements
  3. Comparing Techniques – Direct Measurements
  4. Transduction Method – Piezoresistive
  5. Transduction Method – Piezoelectric
  6. Transduction Method – Capacitive
  7. Transduction Method – Optical
  8. Transduction Method – Summary and Guidelines
  9. Sensor Construction – Conventional
  10. Sensor Construction – MEMS
  11. Summary and References


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