Design and qualification of an unsteady low-speed wind tunnel with an upstream louver system

Farnsworth, John; Sinner, Daniel; Gloutak, Dasha; Droste, Lucas; Bateman, Daniel

doi:10.1007/s00348-020-03018-1

Cited by 24 publications

(6 citation statements)

References 27 publications

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“…Experiments were conducted in the closed test section configuration of the unsteady, low-speed wind tunnel facility at the University of Colorado Boulder (Farnsworth et al 2020). A set of upstream louvers generated time-varying, sinusoidal streamwise velocities, u(t) = u (1 + σ sin(ωt)), where u is the time-averaged velocity, σ is the normalized amplitude, ω = 2π f is the radial frequency, and f is the temporal frequency.…”

Section: Methodsmentioning

confidence: 99%

Vortex Dynamics of a Separated Wing in a Time-Varying Freestream

Gloutak

Jansen

Farnsworth

2023

Preprint

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Unsteady flows threaten the performance and efficiency of systems operating in gusty environments. The impact of an unsteady freestream, generated in a closed test-section unsteady wind tunnel, on the flow separation and aerodynamic performance of a wing at a post-stall angle of attack is examined within the current study. Synchronized two-dimensional, high-speed particle image velocimetry and integrated surface pressure measurements were collected for a finite-span wing in a time-varying, spatially uniform freestream. Freestream accelerations impose additional unsteady pressure gradients within the wind tunnel that alter the behavior of shed vortical structures within the separated flow above the wing. Freestream acceleration and conservation of circulation determine the orientation and interaction of shed vortical structures, which alter the magnitude of the fluctuations in the lift force and pitching moment experienced by the wing. Specifically, fluctuations in the sectional lift and pitching moment coefficients are amplified during deceleration and attenuated during acceleration.

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Section: Methodsmentioning

confidence: 99%

Vortex Dynamics of a Separated Wing in a Time-Varying Freestream

Gloutak

Jansen

Farnsworth

2023

Preprint

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“…The streamwise gusts in wind tunnels are usually created by actuating a series of louvers to increase the overall pressure loss in the wind tunnel circuit leading to a time-varying freestream velocity [5,6]. For a blow-down wind tunnel configuration, the louvers can be installed either upstream [7,8] or downstream of the test section [5]. For an Eiffel-type wind tunnel configuration and a closed-return wind tunnel configuration, the louvers are usually located downstream of the test section [4,6].…”

Section: Gust Types and Unsteady Wind Tunnelsmentioning

confidence: 99%

“…For an Eiffel-type wind tunnel configuration and a closed-return wind tunnel configuration, the louvers are usually located downstream of the test section [4,6]. Due to the non-linear dependency between pressure and velocity, achieving a sinusoidally varying freestream in the test section depends on several factors such as louver location in the tunnel circuit, louver distance from the test section, and acceleration limits of the louver system [5,6,8]. Hence, as a part of this study, the shuttering system in the UD-LSWT is characterized to ensure sinusoidal variation in a streamwise gust in the open-jet test section.…”

Section: Gust Types and Unsteady Wind Tunnelsmentioning

confidence: 99%

“…Most of the aforementioned unsteady wind tunnels have a closed jet test section, except for the facility at the University of Colorado Boulder [7,8] where the testing section can be swapped between an open jet and closed jet configuration, very similar to the UD-LSWT. The characterization results indicated that the temporal variability in freestream velocity between closed-jet and open-jet configurations was significantly different.…”

Section: Gust Types and Unsteady Wind Tunnelsmentioning

confidence: 99%

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Frequency Response of RC Propellers to Streamwise Gusts in Forward Flight

Cai

Gunasekaran

2023

Wind

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The RC propeller performance under steady and sinusoidally time-varying freestream (stream-wise or longitudinal gust) was investigated in the University of Dayton Low-Speed Wind Tunnel (UD-LSWT) in the open-jet configuration. The propellers were tested at varying incidence angles and reduced frequencies. The streamwise gust was created by actuating the shuttering system located at the test section exit and was characterized using hot-wire anemometry. A system identification model was developed for the shuttering system to determine the shutter actuation profile that would result in a sinusoidal gust in the test section. Changes in propeller thrust, power, and pitching moment were observed with an increase in propeller incidence angle under the steady freestream. The propeller’s steady freestream performance was then used to predict response under periodic streamwise gusts in edgewise flight. Below a reduced frequency of 0.2, the propeller response agrees with the prediction model, suggesting that the propeller response is quasi-steady. At reduced frequencies higher than 0.2, a reduction in mean thrust and pitching moment and significant phase lag was observed.

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“…Literature regarding dynamic stall was initially motivated by helicopter rotor aerodynamics and flutter [5,6,7], and received renewed interest due to problems related to gust interactions [8,9]. The main parameter governing flow unsteadiness related to the kinematics of a pitching airfoil is the reduced pitch rate k defined as:…”

Section: Introductionmentioning

confidence: 99%

The dynamics and timescales of static stall

Fouest,

Deparday,

Mulleners

2021

Preprint

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Airfoil stall plays a central role in the design of safe and efficient lifting surfaces. We typically distinguish between static and dynamic stall based on the unsteady rate of change of an airfoil's angle of attack. Despite the somewhat misleading denotation, the force and flow development of an airfoil undergoing static stall are highly unsteady and the boundary with dynamic stall is not clearly defined. We experimentally investigate the forces acting on a two-dimensional airfoil that is subjected to two manoeuvres leading to static stall: a slow continuous increase in angle of attack with a reduced pitch rate of 1.3 × 10 −4 and a step-wise increase in angle of attack from 14.2°to 14.8°within 0.04 convective times. We systematically quantify the stall reaction delay, or the timespan between the moment the blade exceeds its critical static stall angle and the onset of stall, for many repetitions of these two manoeuvres. The onset of flow stall is marked by the distinct drop in the lift coefficient. The reaction delay for the slow continuous ramp-up manoeuvre is not influenced by the blade kinematics and its occurrence histogram is normally distributed around 32 convective times.The static reaction delay is compared with dynamic stall delays for dynamic ramp-up motions with reduced pitch rates ranging from 9 × 10 −4 to 0.14 and for dynamic sinusoidal pitching motions of different airfoils at higher Reynolds numbers up to 1 × 10 6 . The stall delays for all conditions follows the same power law decrease from 32 convective times for the most steady case down to an asymptotic value of 3 convective times for reduced pitch rates above 0.04. Static stall is not phenomenologically different than dynamic stall and is merely a typical case of stall for low pitch rates where the onset of flow separation is not promoted by the blade kinematics. Based on our results, we suggest that conventional measurements of the static stall angle and the static load curves should be conducted using a continuous and uniform ramp-up motion at a reduced frequency around 1 × 10 −4 .

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Design and qualification of an unsteady low-speed wind tunnel with an upstream louver system

Cited by 24 publications

References 27 publications

Vortex Dynamics of a Separated Wing in a Time-Varying Freestream

Vortex Dynamics of a Separated Wing in a Time-Varying Freestream

Frequency Response of RC Propellers to Streamwise Gusts in Forward Flight

The dynamics and timescales of static stall

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