Measuring Shear Stress with a Microfluidic Sensor to improve Aerodynamic Efficiency

Skin friction drag is directly proportional to the local shear stress of a surface and can be the largest factor in an aerodynamic body's total parasitic drag. The measurements of the local shear stress has long been a difficult measurement in an air-flow environment due to the interaction between the sensor and air flow. In order for modern researchers to further improve the efficiency of aircraft and other aerodynamic bodes, sensitive measurements in the smallest scale possible are required. To achieve this goal, the measurement community has turned towards micro-electrical mechanical systems which utilize microscopic moving parts to directly measure the shear stress. Unfortunately the cost, sensitivity, and packaging have proven to be insurmountable challenges in sensor development. Our company proposes a paradigm shift in shear stress measurements that will take advantage of the complete sensing package offered in MEMS without the need for moving mechanical parts or expensive manufacturing. Our patent pending sensor will allow us to measure the shear stress at a wall using microfluidic principles and fluid-structure interactions. In our proposed sensor, highly sensitive electrochemical measurements measure the vibrations induced in a membrane by the external shear stress. Because of the nature of electrochemical measurements, the relationship between size and sensitivity is reversed compared to MEMS sensing methods. As our sensor decreases in size, the current change induced in the system increases, resulting in a sensitivity limit imposed only by manufacturing limits. We believe that this sensor will have the ability to obtain real-time shear stress measurements across the range of external air flows. Due to the absence of moving parts within our proposed system, we believe that the sensor will be significantly more robust and durable for many different applications. At the conclusion of this project, we expect to move this technology from TRL-2 to TRL-4.

The principal application to this sensor is in a wind tunnel environment. To date, there has been no other shear stress sensor that has offered sensing at the micron scale, while achieving accuracy independent of air quality and environmental factors. Our proposed sensor will help experimentalists measure and minimize important design considerations such as skin drag. Additionally, the increased information at the surface of aerodynamic bodies will help the computational fluid dynamics community validate and refine their models. Another possible application could be real-time shear stress measurements for morphing wing control systems. Wing designs which change shape depending on conditions are a new branch of research in the aerospace community. Real time shear stress measurements could become an integral part of these wing's control systems. With the proposed designs and our proposed sensors, wings could change their aerodynamic characteristics based on real time information from our sensors. Skin drag accounts for over half of airplane efficiency losses and a 5% increase in efficiency could have billions of dollars in fuel savings. Historically, skin drag has been difficult to measure locally due to measurement interference with important variables. Our sensor has little to no interaction with the external air flow, therefore giving the most pure measurement of shear stress as the smallest scale.

Once our sensor concept has been proved, we expect to be able to extend the shear stress measurements to watercraft. This could have a profound effect on ship and submarine design and ultimately increase their efficiency. As with the aerospace community, a small increase in efficiency could save billions in fuel costs. Another possible application could be in the energy industry. Coal, gas and nuclear power plants could benefit from pipe flow optimization or real time shear stress measurements. The monitoring of shear stress at a wall of a pipe could be the first indicator of corrosion or other fouling within the cooling system.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.