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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

Flow in the test section remains stable over the operating range and uniform in both magnitude and direction. (a) A range of airspeeds, U, measured by pressure ports in the stilling chamber and contraction are shown while the fan operates at fixed speeds (r.p.m.). The zoomed inserts show how instantaneous airspeed differs slightly from the mean airspeed, . The standard deviation of U ranges from 0.017 m s−1 when  = 10 to 0.060 m s−1 when  = 50 m s−1. The maximum speed (50 m s−1) was checked with additional airspeed data from a Pitot-static probe at the test section centreline. (b) The deviation in airspeed from the average airspeed, ΔU, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are comparable between the 10 m s−1 airspeed case ((i) 1σ of ΔU = 0.020 m s−1) and the 25 m s−1 airspeed case ((ii) 1σ of ΔU = 0.023 m s−1). Colour indicates the relative airspeed deviation, that is, . (c) The angle between the flow vector and a streamwise unit vector, Δθ, is measured on a 4 × 4 grid in the test section (black arrows indicate grid points). The arrows show the direction of the flow velocity projected into the plane of the grid (z–y-plane). The flow shows a slight tendency to diverge at the plane of the grid but is primarily straight for both the 10 m s−1 airspeed case ((i) 1σ of Δθ = 0.13°) and the 25 m s−1 airspeed case ((ii) 1σ of Δθ = 0.14°).
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RSOS160960F2: Flow in the test section remains stable over the operating range and uniform in both magnitude and direction. (a) A range of airspeeds, U, measured by pressure ports in the stilling chamber and contraction are shown while the fan operates at fixed speeds (r.p.m.). The zoomed inserts show how instantaneous airspeed differs slightly from the mean airspeed, . The standard deviation of U ranges from 0.017 m s−1 when  = 10 to 0.060 m s−1 when  = 50 m s−1. The maximum speed (50 m s−1) was checked with additional airspeed data from a Pitot-static probe at the test section centreline. (b) The deviation in airspeed from the average airspeed, ΔU, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are comparable between the 10 m s−1 airspeed case ((i) 1σ of ΔU = 0.020 m s−1) and the 25 m s−1 airspeed case ((ii) 1σ of ΔU = 0.023 m s−1). Colour indicates the relative airspeed deviation, that is, . (c) The angle between the flow vector and a streamwise unit vector, Δθ, is measured on a 4 × 4 grid in the test section (black arrows indicate grid points). The arrows show the direction of the flow velocity projected into the plane of the grid (z–y-plane). The flow shows a slight tendency to diverge at the plane of the grid but is primarily straight for both the 10 m s−1 airspeed case ((i) 1σ of Δθ = 0.13°) and the 25 m s−1 airspeed case ((ii) 1σ of Δθ = 0.14°).

Mentions: The airspeed in the test section remained stable over the full operating range (0–50 m s−1; figure 2a). To test stability, airspeed was recorded for 240 s at 1 Hz from the calibrated pressure ports. Seven set point airspeeds were considered over the operating range: 5, 10, 20, 25, 30, 40 and 50 m s−1. Airspeed was more steady at the lowest speed (1σ = 0.017 m s−1) than the highest speed (1σ = 0.060 m s−1), but all airspeeds remained stable to within less than 0.2% of the mean. The highest airspeed value (50 m s−1) was confirmed using measurements from the Pitot-static probe at the centreline.Figure 2.


A new low-turbulence wind tunnel for animal and small vehicle flight experiments
Flow in the test section remains stable over the operating range and uniform in both magnitude and direction. (a) A range of airspeeds, U, measured by pressure ports in the stilling chamber and contraction are shown while the fan operates at fixed speeds (r.p.m.). The zoomed inserts show how instantaneous airspeed differs slightly from the mean airspeed, . The standard deviation of U ranges from 0.017 m s−1 when  = 10 to 0.060 m s−1 when  = 50 m s−1. The maximum speed (50 m s−1) was checked with additional airspeed data from a Pitot-static probe at the test section centreline. (b) The deviation in airspeed from the average airspeed, ΔU, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are comparable between the 10 m s−1 airspeed case ((i) 1σ of ΔU = 0.020 m s−1) and the 25 m s−1 airspeed case ((ii) 1σ of ΔU = 0.023 m s−1). Colour indicates the relative airspeed deviation, that is, . (c) The angle between the flow vector and a streamwise unit vector, Δθ, is measured on a 4 × 4 grid in the test section (black arrows indicate grid points). The arrows show the direction of the flow velocity projected into the plane of the grid (z–y-plane). The flow shows a slight tendency to diverge at the plane of the grid but is primarily straight for both the 10 m s−1 airspeed case ((i) 1σ of Δθ = 0.13°) and the 25 m s−1 airspeed case ((ii) 1σ of Δθ = 0.14°).
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Related In: Results  -  Collection

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Show All Figures
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RSOS160960F2: Flow in the test section remains stable over the operating range and uniform in both magnitude and direction. (a) A range of airspeeds, U, measured by pressure ports in the stilling chamber and contraction are shown while the fan operates at fixed speeds (r.p.m.). The zoomed inserts show how instantaneous airspeed differs slightly from the mean airspeed, . The standard deviation of U ranges from 0.017 m s−1 when  = 10 to 0.060 m s−1 when  = 50 m s−1. The maximum speed (50 m s−1) was checked with additional airspeed data from a Pitot-static probe at the test section centreline. (b) The deviation in airspeed from the average airspeed, ΔU, is measured on a 4 × 4 grid in the test section (black dots indicate grid points). Deviations are comparable between the 10 m s−1 airspeed case ((i) 1σ of ΔU = 0.020 m s−1) and the 25 m s−1 airspeed case ((ii) 1σ of ΔU = 0.023 m s−1). Colour indicates the relative airspeed deviation, that is, . (c) The angle between the flow vector and a streamwise unit vector, Δθ, is measured on a 4 × 4 grid in the test section (black arrows indicate grid points). The arrows show the direction of the flow velocity projected into the plane of the grid (z–y-plane). The flow shows a slight tendency to diverge at the plane of the grid but is primarily straight for both the 10 m s−1 airspeed case ((i) 1σ of Δθ = 0.13°) and the 25 m s−1 airspeed case ((ii) 1σ of Δθ = 0.14°).
Mentions: The airspeed in the test section remained stable over the full operating range (0–50 m s−1; figure 2a). To test stability, airspeed was recorded for 240 s at 1 Hz from the calibrated pressure ports. Seven set point airspeeds were considered over the operating range: 5, 10, 20, 25, 30, 40 and 50 m s−1. Airspeed was more steady at the lowest speed (1σ = 0.017 m s−1) than the highest speed (1σ = 0.060 m s−1), but all airspeeds remained stable to within less than 0.2% of the mean. The highest airspeed value (50 m s−1) was confirmed using measurements from the Pitot-static probe at the centreline.Figure 2.

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