By Adam Kahraman

When testing in a wind tunnel, you probably wish that the air was visible. Imagine being able to see laminar and turbulent flow as they happen, without the mess of smoke or running a massive CFD simulation. What if there was a tool that allowed you to “see” the wind in real time?

The WindProbe was designed to fulfill that wish. It captures wind profiles with high temporal resolution across multiple angles, while integrated motion tracking pinpoints exactly where the measurement was taken.

In this article, we demonstrate the tool’s use cases, how it works and the practical gains it offers in your wind tunnel testing workflow.

Table of Contents

1. Introduction
2. Common Wind Measurement Problems
3. How the WindProbe 3D Works
4. Practical Application: Simulating Shear Wind
5. Conclusion

Figure 1: Full length view of the WindProbe with motion tracking reflectors visible

Common Wind Measurement Problems

There are various ways to perform flow visualization such as using a smoke machine, lasers, or tufts. All of these have their advantages and disadvantages, but the most common limitation is that they primarily rely on visual observation as a means of measurement rather than producing quantitative data.

Measuring airflow around a specific object adds another layer of problems.

• The setup has to be built around the shape of that object.
• Tufts need to be attached to the surface.
• Smoke has to be aimed at specific points around the object.
• Probes need to be arranged around the object.

Another common use of wind tunnels is validating CFD simulation results, however that also has its set of problems.

• Small differences in the physical setup can cause the real airflow to behave differently than the simulation predicted.
• There is no straightforward way to check whether the two actually match.
• Without a way to measure the full wind profile, you are largely assuming the transfer was accurate.

How the WindProbe 3D Works

Despite the complex challenges it solves, the WindProbe itself has a simple design. It is a multi-hole pressure sensor with five holes at the tip with a 40-degree acceptance cone.

Figure 2: WindProbe with the 40° acceptance cone represented in scale

The acceptance cone allows the WindProbe to measure wind hitting the tip at various angles, capturing velocity vectors across the x, y, and z axes. Unlike a Pitot tube, which only measures wind flowing directly into it, this multi-hole design captures data across a wide range of directions. This feature is necessary when measuring wind in turbulent conditions.

The WindProbe has an acquisition frequency of 200 Hz. This temporal resolution captures fine details in wind velocity, ensuring you see rapid changes without missing data points between measurements.

Here's a video that shows the WindProbe in action:

The probe comes pre-calibrated and is easy to pair with a WindShaper through a single USB cable for communication and power. The probe can measure wind speeds as low as 1 m/s and up to 60 m/s depending on the model.

The WindProbe’s spatial tracking allows you to move the probe while recording data and plot the recorded values in 3D space. This makes it possible to map the wind profile across the entire test section, both along the downstream axis and across the vertical and horizontal axes of a given plane. Rather than measuring at a single point, the full wind image of the test section can be captured. Furthermore, wind measurements can be taken around any object in the test section, whether that is a propeller, an airfoil, or a drone.

Figure 3: WindProbe capturing wind data in real time while being tracked in 3D

What enables the WindProbe to be tracked in 3D is the motion capture markers placed along the arm of the probe. When paired with motion capture cameras, the system tracks the probe’s exact position in 3D space. 

Figure 4: OptiTrack motion capture markers on the WindProbe

The same markers are placed on the WindShaper, allowing the software to track the probe’s position relative to the wind source.

Figure 5: OptiTrack motion capture markers on the WindShaper

WindVision Software

All data from the WindProbe is handled with the WindVision software, which manages tracking, measurement, and data visualisation. To help you position the probe where it needs to be, the probe has a built-in LED strip that acts as a real-time guide. When you define a measurement plane in the software, the LEDs change colour based on your position: red when you are far away, yellow as you get closer, and green when you are exactly on the plane.

Figure 6: LED strip on the WindProbe lighting up red, yellow and green

WindVision can export data as .csv or .vtk files, which you can open and analyze in a software like ParaView. In WindVision, you define the dimensions of the test section and the measurement plane.

The software also allows you to adjust the spatial resolution of this measurement plane. The plane is divided into units called voxels. Similar to how a 2D image's size and resolution are defined by pixels, a voxel is a 3D representation of a value in space. Increasing the resolution, the number of voxels, provides a higher data granularity and greater insight. Lowering the resolution allows you to complete the measurement faster by filling fewer voxels, providing a broader overview of the flow.

The system can measure velocity vectors in volumes as small as 1 cm3. At this smallest setting, you can work with up to 27 million voxels in your measurement plane, providing high detail of the wind profile. 

Practical Application: Simulating Shear Wind

Let’s say you are designing a drone meant for cleaning windows on tall buildings. Wind speed often increases with altitude, so the upper floors of tall buildings are exposed to much stronger winds. When this wind strikes the building, it creates sharp speed gradients that can produce significant wind shear, which can be difficult for a drone to navigate.

Before taking on this flight over a high density area with expensive windows in the mix, the drone operator may want to get some practice in these conditions,  without risking the drone or the building.

Figure 7: Computer generated image of a wind hitting a building’s face (source)

Fortunately, this environment is easily simulated using a WindShaper. For a 2x2 module setup like the one in the figure below, you can run the left fan modules at 2 m/s and the right modules at 6 m/s. This creates a steep gradient between the two sides, simulating wind shear. The WindProbe then allows you to visualize the wind profile generated by the WindShaper.

Figure 8: WindVision software showing a clear windshear from the WindShaper

By placing the WindProbe in front of the fans, you can begin gathering data. As you move the probe across the plane, the software automatically generates a real-time visualization of the wind profile.

The next step is to fly your drone left to right in front of the machine to see how it responds in these conditions, and practice your recovery.

Conclusion

The WindProbe offers a unique approach to 3D wind measurement for engineers and researchers, turning invisible air into readable data. It provides a level of verification that was previously impossible without complex and expensive equipment. By combining multi-hole pressure sensing and motion tracking, it remains the only tool on the market capable of mapping a full 3D wind profile in real time.

Figure 9: WindProbe 3D scanning flow field behind a fixed wing UAV