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A new low-turbulence wind tunnel for animal and small vehicle flight experiments

View Article: PubMed Central - PubMed

ABSTRACT

Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s−1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s−1. To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.

No MeSH data available.


Related in: MedlinePlus

Temperature and humidity remain stable over the operating range; temperature is uniform in the test section. (a) Temperature in the stilling chamber is shown while a proportional-integral controller regulates a water-chilled heat exchanger to keep the tunnel at 20°C. Dashed lines show the upper and lower limits of the tunnel's operating range. The zoomed insert shows that temperature deviations from the mean temperature, , vary depending on average airspeed, . The standard deviation of T ranges from 0.007°C when  = 10 m s−1 to 0.073°C when  = 50 m s−1. (b) Relative humidity is recorded during tunnel operation. One trial ( = 20 m s−1) was conducted on a different day, resulting in a different average humidity (approx. 63%) than the other trials (approx. 32–34%). The zoomed insert shows that relative humidity changes only slightly with no clear dependence on airspeed; the average standard deviation across the seven airspeeds tested was 0.08%. (c) The deviation in temperature from the average tunnel temperature, ΔT, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are slightly lower when  = 10 m s−1 ((i) 1σ of ΔT = 0.015°C) compared with when  = 25 m s−1 ((ii) 1σ of ΔT = 0.074°C). Colour indicates the relative temperature deviation, that is, .
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RSOS160960F3: Temperature and humidity remain stable over the operating range; temperature is uniform in the test section. (a) Temperature in the stilling chamber is shown while a proportional-integral controller regulates a water-chilled heat exchanger to keep the tunnel at 20°C. Dashed lines show the upper and lower limits of the tunnel's operating range. The zoomed insert shows that temperature deviations from the mean temperature, , vary depending on average airspeed, . The standard deviation of T ranges from 0.007°C when  = 10 m s−1 to 0.073°C when  = 50 m s−1. (b) Relative humidity is recorded during tunnel operation. One trial ( = 20 m s−1) was conducted on a different day, resulting in a different average humidity (approx. 63%) than the other trials (approx. 32–34%). The zoomed insert shows that relative humidity changes only slightly with no clear dependence on airspeed; the average standard deviation across the seven airspeeds tested was 0.08%. (c) The deviation in temperature from the average tunnel temperature, ΔT, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are slightly lower when  = 10 m s−1 ((i) 1σ of ΔT = 0.015°C) compared with when  = 25 m s−1 ((ii) 1σ of ΔT = 0.074°C). Colour indicates the relative temperature deviation, that is, .

Mentions: The temperature and relative humidity remained stable over the full operating range (0–50 m s−1; figure 3a). To test stability, temperature and humidity were recorded by the facility probes in the stilling chamber (240 s at 1 Hz). Seven set point airspeeds were considered over the operating range: 5, 10, 20, 25, 30, 40 and 50 m s−1. Temperature was more steady at the lowest speed (1σ = 0.007°C) than the highest speed (1σ = 0.073°C), but all temperatures remained stable to within less than 0.4% of the mean. The stability of temperature demonstrates the effectiveness of the manually tuned proportional-integral controller and the constant flow heat exchanger. As relative humidity was not actively controlled, its value is primarily a function of the ambient laboratory conditions. For example, the 20 m s−1 condition was measured on a different day than the other airspeeds, resulting in the different humidity value recorded for that airspeed.Figure 3.


A new low-turbulence wind tunnel for animal and small vehicle flight experiments
Temperature and humidity remain stable over the operating range; temperature is uniform in the test section. (a) Temperature in the stilling chamber is shown while a proportional-integral controller regulates a water-chilled heat exchanger to keep the tunnel at 20°C. Dashed lines show the upper and lower limits of the tunnel's operating range. The zoomed insert shows that temperature deviations from the mean temperature, , vary depending on average airspeed, . The standard deviation of T ranges from 0.007°C when  = 10 m s−1 to 0.073°C when  = 50 m s−1. (b) Relative humidity is recorded during tunnel operation. One trial ( = 20 m s−1) was conducted on a different day, resulting in a different average humidity (approx. 63%) than the other trials (approx. 32–34%). The zoomed insert shows that relative humidity changes only slightly with no clear dependence on airspeed; the average standard deviation across the seven airspeeds tested was 0.08%. (c) The deviation in temperature from the average tunnel temperature, ΔT, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are slightly lower when  = 10 m s−1 ((i) 1σ of ΔT = 0.015°C) compared with when  = 25 m s−1 ((ii) 1σ of ΔT = 0.074°C). Colour indicates the relative temperature deviation, that is, .
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Related In: Results  -  Collection

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RSOS160960F3: Temperature and humidity remain stable over the operating range; temperature is uniform in the test section. (a) Temperature in the stilling chamber is shown while a proportional-integral controller regulates a water-chilled heat exchanger to keep the tunnel at 20°C. Dashed lines show the upper and lower limits of the tunnel's operating range. The zoomed insert shows that temperature deviations from the mean temperature, , vary depending on average airspeed, . The standard deviation of T ranges from 0.007°C when  = 10 m s−1 to 0.073°C when  = 50 m s−1. (b) Relative humidity is recorded during tunnel operation. One trial ( = 20 m s−1) was conducted on a different day, resulting in a different average humidity (approx. 63%) than the other trials (approx. 32–34%). The zoomed insert shows that relative humidity changes only slightly with no clear dependence on airspeed; the average standard deviation across the seven airspeeds tested was 0.08%. (c) The deviation in temperature from the average tunnel temperature, ΔT, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are slightly lower when  = 10 m s−1 ((i) 1σ of ΔT = 0.015°C) compared with when  = 25 m s−1 ((ii) 1σ of ΔT = 0.074°C). Colour indicates the relative temperature deviation, that is, .
Mentions: The temperature and relative humidity remained stable over the full operating range (0–50 m s−1; figure 3a). To test stability, temperature and humidity were recorded by the facility probes in the stilling chamber (240 s at 1 Hz). Seven set point airspeeds were considered over the operating range: 5, 10, 20, 25, 30, 40 and 50 m s−1. Temperature was more steady at the lowest speed (1σ = 0.007°C) than the highest speed (1σ = 0.073°C), but all temperatures remained stable to within less than 0.4% of the mean. The stability of temperature demonstrates the effectiveness of the manually tuned proportional-integral controller and the constant flow heat exchanger. As relative humidity was not actively controlled, its value is primarily a function of the ambient laboratory conditions. For example, the 20 m s−1 condition was measured on a different day than the other airspeeds, resulting in the different humidity value recorded for that airspeed.Figure 3.

View Article: PubMed Central - PubMed

ABSTRACT

Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s−1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s−1. To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.

No MeSH data available.


Related in: MedlinePlus