We will quick off this series of technical articles and use-cases with a detailed explanation of our technology to help you better grasp the main features and advantages of WindShape’s flagship product.

Windshapers are the core of WindShape’s ecosystem as well as one of the most sought-after technologies in aerodynamic testing in recent years, but what are they exactly? The terms ‘mult-fan wind generator’, ‘fan-array wind tunnels’ and ‘3D wind flow creator’ are all accurate, but they don’t fully capture what windshapers can do.

In this article we will explain what a windshaper is, how it works, and how it’s an improvement for drone testing and other aerodynamics research. Here’s an overview:

Table of Contents

  1. What is a Windshaper (concept and structure)
  2. How to Control the Windshaper
  3. What Kinds of Wind Shapes Can I Produce?
  4. Advantages and Disadvantages
  5. The WindShape ecosystem (motion tracking, flow filters, etc.)

Figure 1: A fixed-wing drone flying in front of a 12 x 8 module Windshaper.

 

1. What is a Windshaper

A Windshaper is a new type of aerodynamic test facility based on a large number of small fans used jointly to generate complex air flows in a laboratory environment.

The key component of a Windshaper is its main wall of fans that produces wind profiles for testing drones and other objects in various meteorological conditions. The types of tests possible include free flight tests, aerodynamics measurements, and many more.

Windshapers are highly modular in shape, as they are composed of base units called ‘wind modules’ that can be stacked and combined to create walls of fans of any dimensions. The size of the windshaper is described by the number of modules it contains, i.e. a 6 x 3 windshaper would be 6 modules wide by 3 modules tall.

Each wind module measures about 25 x 25 cm and contains 9 individual wind pixels. Each wind pixel is composed of two counter rotating fans that can be controlled individually, meaning a 6 x 3 windshaper contains 324 individually controllable fans. Fans can produce a wind speed of up to 16 m/s (60 km/h), or up to more than 55 m/s (200 km/h) with a convergent (depending on the size of the Windshaper). Due to their small size, the wind pixels are highly reactive compared to traditional wind tunnel fans, meaning their instantaneous speed can vary very quickly. This enables users to generate highly dynamic 3D flows such as gusts that were previously hard to replicate in a laboratory setting.

Figure 2: A 2 x 2 Windshaper with a wind module and wind pixel highlighted.

In addition to the main wall of fans (1), users can add side walls (2) to generate crosswinds and diversify the testing possibilities. The other key components include the power distribution boxes (3), and onboard computer (4), all seen in figure 3 below.

Figure 3: The main components of a Windshaper.

What you’ve likely noticed is that these Windshapers come in all shapes and sizes – some can fit on your desk while others require their own lab space (see Figure 4).

Figure 4: A series of Windshapers ranging from a 2 x 2 modules (top left), a 6 x 3 (top right), a 8 x 8 (bottom left) and a 12 x 12 (bottom right).

2. How to Control the Windshaper

The Windshaper is controlled with the WindControl software, whose GUI is pictured below (figure 4). The PWM legend at the far right indicates the power supplied and each pale blue square represents a single wind pixel (fan unit). The fans used on the machine comprise two layers of counter rotating rotors, called fan layers. By default, both layers are set to the same speed or PWM value. This achieves the best performance and lowest swirl level, but if desired, fan layers can be controlled independently.

In this particular Windshaper, there is a main wall measuring 12 modules wide by 8 modules high, plus two side walls measuring 2 modules by 8 modules, giving you a total of 1152 wind pixels, or 2304 individually controllable fans. All three walls can be controlled simultaneously using either manual control or the advanced Python API.

Figure 5: The WindControl web interface

Manually controlling the wall is as simple as selecting the desired wind pixels with a mouse click and typing in speed values for these individual pixels (or groups of pixels). When the user is ready to change again the power to a group of pixels, they simply select those pixels and type in a new value, offering dynamic control of the Windshaper. You can also input a mathematical function to have the machine reproduce any steady or time-variable wind profile.

A Python API is also provided with the machine that allows the user to program automated tests. The wind flow can be designed ahead of time and run independently without intervention. This allows the user to focus on controlling the aircraft / airfoil or observing the test. The Python API also allows users to generate more complex flow, and to interface the Windshaper directly with other systems (drone, tracking cameras, connected probes, …) for real-time flow corrections.

Once tests are completed, data from each wind module can be output into a zip folder on the home computer containing time-stamped information about the Windshaper’s performance and status.

3. What Kinds of Wind Shapes Can I Produce?

With a Windshaper you can create a number of wind situations, both constant and time-variable. Here are a few of the basic categories of wind shapes that can be used alone or in combination.

Steady Flow

This setting mimics the constant flow you are mostly likely to see in a traditional wind tunnel, which is great for evaluating the aerodynamics of a drone. A steady condition is generated by setting the Windshaper’s flow speed to the speed the drone would be traveling in still air, while the drone maintains its position above the ground. In this scenario, the relative wind speed, as seen by the drone, is equivalent to the speed the drone would be flying. A flow straightener may be used to achieve a wind flow with a lower turbulence level.

Figure 6: A drone flying in steady flow.

Turbulent Flow

Turbulent flow is ideal for simulating the conditions a drone is likely to face in its work environment due to weather and topology. At the altitude drones typically fly, it is unlikely they will experience laminar flow. In this test setting, the level of turbulence can be controlled by modulating the power delivered to each wind pixel. The turbulence level can be equal across the Windshaper or different in each section of the test area.

Figure 7: A drone flying in turbulent wind conditions.

Shear Flow

The term ‘shear flow’ describes a wind profile where adjacent layers of fluids move parallel to each other at different speeds. This can lead to flow instabilities near walls, foliage or in regions with noticeable thermal effects. This can be simulated by setting wind pixels on one fan array to a slow wind speed and setting wind pixels on an adjacent fan array to a higher wind speed. This technology also enables users to easily generate a boundary layer without needing to use traditional boundary layer generators such as roughness blocks or spires that are found in traditional wind tunnels.

Figure 8: A group of drones flying in an environment with wind shear.

Time Variable Flow

With time variable flows you can create unique wind profiles by changing the wind speed of each wind pixel over time. A given wind pixel may begin at 2 m/s, increase to 10 m/s, then return to 2 m/s and so on. With this level of control you can create wind shapes that simulate real-life flying conditions, like a vehicle passing a drone (figure 9).

Wind Gust

Sudden changes in wind speed (gusts) can be challenging for a drone to navigate. Gusts can be simulated with rapid changes in wind speed coming from the wind pixels. This allows you to study drone displacement or resistance to gusts, and the responsivity of the flight controller. Adding additional side walls to the Windshaper is another way to simulate gusts and crosswinds.

Figure 10: A drone experiences a gust of wind as it flies around a building.

Vertical Wind / Landing Phase Optimization

While landing, drones experience a relative wind from below caused by their own wake (downwash), which leads to an unstable situation. To simulate this situation, the Windshaper is placed horizontally and generates a wind flow equivalent to the drone’s downwash.

As you can see, there is a great variety of wind shapes you can produce with these Windshapers, and this article doesn’t even cover them all. If you have a specific type of test in mind, contact our sales department to see what is possible.

Figure 11: A drone practicing landings.

4. Advantages and Disadvantages

There are several advantages and disadvantages to working with a Windshaper for drone testing and validation. Here are a few of the most important ones:

Advantages

  • Controllability and repeatability of tests: when performing a test flight outdoors, the weather and wind can be unpredictable, making it hard to get repeatable results. With a Windshaper you can program your wind conditions to perform the same test again and again.
  • Convenience: The Windshaper is on wheels, so it is easily moved and positioned where needed. It also takes very little storage space thanks to its compact shape, compared to traditional wind tunnel which can occupy a full building.
  • Large testing space: the modular design of the Windshaper means you can build a test area as big as you need. This allows you to test full size aircraft or even multiple aircraft to test formation flying.
  • Time variable flows: since each wind pixel is controlled individually, it is possible to create time variable flows across the testing space, something that is not possible when using a single fan in a traditional wind tunnel. This adds the possibility of replicating complex atmospheric flows that vary both in time and space.
  • Free flight testing: the design of the Windshaper provides enough space for the drone to fly in front of it while staying within the programmed wind flow. This contrasts with most traditional wind tunnels that require the drone to be stationary in the tunnel or bound in some way to avoid collisions with nearby walls.
  • Infinite testing possibilities: since each wind pixel is controlled individually, there is a nearly infinite number of testing possibilities, including variations on turbulence, gusts, thermal effects, and more
  • Atmospheric flow replication: traditional wind tunnels try to generate the most uniform and low-turbulence flow possible. However, real outdoor winds are highly turbulent, non-uniform in space, and also unsteady with respect to time. The high dynamic response and individual control of the wind pixels comprising a Windshaper mean that real-life wind conditions can be replicated in full-scale inside a laboratory setting.
  • Horizontal and vertical testing in one: with the added tilting capability of the Windshaper, it can be used as both a horizontal and vertical wind source. With a traditional wind tunnel, this would require building two separate facilities.
  • Uniformity on demand: flow uniformity can be tweaked with software to ensure a perfectly flat profile across the test section, unlike traditional wind tunnels.

Figure 12: A quadcopter being tested with a 12 x 12 Windshaper.

Disadvantages

  • Wind speed is limited: Windshapers allow for a maximum wind speed of 16 m/s (60 kph), or up to 55 m/s (200 kph) with a convergent. While this is suitable for testing most drones and many other aerodynamic applications, it does not reach transonic or supersonic speeds.
  • Turbulence level: compared to aeronautic grade wind tunnels, the turbulence intensity of a Windshaper is not as low (approximately 5%). But an optional flow filter (see section 5) can be used to lower the turbulence level below 1%.
  • Noise: due to their small fans, Windshapers will generate a higher frequency noise compared to traditional wind tunnels. But since this noise is high frequency, it will not propagate as far, and can be easily stopped by a concrete wall or a pair of earplugs (compared to other large wind tunnels that can shake a whole building and need dampers to operate properly).

5. Compatible Systems

The Windshaper has several complementary systems that can enhance your drone testing. Contact our sales team for more information about any of these add-ons

Convergent

A convergent device allows you to increase your maximum wind speed from 16 m/s (60 kph) up to 45 m/s (160 kph). The convergent attaches to the front of the Windshaper and accelerate the air flow. Note that this device will reduce your test area size, depending on the size of the Windshaper. Adding a divergent after the test section (as in figure 14) can further increase wind speed past 55 m/s (200 kph).

Figure 13: Picture of a convergent and divergent canal attached to a 6 x 3 module Windshaper. This configuration can generate winds up to more than 55 m/s (200 kph).

Flow Filter / Turbulence Reduction

A flow filter can be added to your Windshaper to reduce unwanted turbulence and ensure a low turbulence intensity. This feature ensures an even flow of air and is a great option for more traditional aerodynamics testing using force or pressure measurements, which can benefit from a lower signal to noise ratio.

Tilting mechanism

The tilting mechanism add-on allows you to rotate your Windshaper 90 degrees, so it can be standing vertically or laying horizontally. This is a great setup for simulating the effects of thermals, ground effect, and practicing landings in different conditions. It is not only a tool for measuring your drone’s performance, but also for allowing your pilots to refine their skills.

Connected probes

To really enter the aerodynamic testing of the 21st century, WindShape propose a series of probes that can be directly connected to the Windshaper, allowing real-time flow corrections to ensure test conditions. Such probes include Streamwise’s PROCAP system, an optically tracked multi-hole probe.

Conclusion

If you have any remaining questions, leave us a comment below and we will be sure to get back to you.

If you’re interested in purchasing a Windshaper, you can request a quote from our sales team.