Buffeting of large telescopes: Wind-tunnel measurements of the flow inside a generic enclosure

Pottebaum, Tait; MacMynowski, Douglas G.

doi:10.1016/j.jfluidstructs.2005.08.005

Cited by 8 publications

(15 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The M2 flow-field wind-tunnel test 6 collected data within a scaled telescope enclosure to understand the flow field around the region near the dome opening where M2 and its supporting structure would be subjected to wind loads. The model was representative of a generic empty telescope dome at approximately 1% of the expected full-scale enclosure size for a 30 m diameter telescope.…”

Section: B Wind Tunnel Testsmentioning

confidence: 99%

“…The most significant error source in the DPIV data is the difference between the measured particle velocities and the actual flow velocities in regions of high flow acceleration where the particles may not accurately follow the flow. 6 Significant errors are possible near the dome opening, and thus the predicted loads on M2 are computed from the error bound rather than the measured velocity.…”

Section: B Wind Tunnel Testsmentioning

confidence: 99%

“…[3][4][5] More extensive data under more controlled conditions have been collected in an ϳ1% scale wind-tunnel experiment. 6 Finally, computational fluid dynamic (CFD) analyses 7 have been validated against these data sources and used primarily to understand differences between different sources of data.…”

Section: Introductionmentioning

confidence: 99%

“…12 Significantly more data have been collected in recent tests, leading to both better understanding of the flow field and quantitative information that can be used in modeling and design. Digital particle image velocimetry (DPIV) can provide a quantitative spatial map of the flow field in the region around the secondary mirror, 6 while arrays of pressure measurements across the primary mirror can be used to understand the spatial variation. 13 In addition to the wind-tunnel tests on hemispherical domes that are used to develop the understanding herein, others have recently been conducted for a different dome geometry.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Wind loads on ground-based telescopes

et al. 2006

View full text Add to dashboard Cite

One of the factors that can influence the performance of large optical telescopes is the vibration of the telescope structure due to unsteady wind inside the telescope enclosure. Estimating the resulting degradation in image quality has been difficult because of the relatively poor understanding of the flow characteristics. Significant progress has recently been made, informed by measurements in existing observatories, wind-tunnel tests, and computational fluid dynamic analyses. We combine the information from these sources to summarize the relevant wind characteristics and enable a model of the dynamic wind loads on a telescope structure within an enclosure. The amplitude, temporal spectrum, and spatial distribution of wind disturbances are defined as a function of relevant design parameters, providing a significant improvement in our understanding of an important design issue.

show abstract

Section: B Wind Tunnel Testsmentioning

confidence: 99%

Section: B Wind Tunnel Testsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Wind loads on ground-based telescopes

et al. 2006

View full text Add to dashboard Cite

show abstract

“…3,4 Previous models of wind loading on the telescope structure for TMT have been based on a parametric model [4][5][6] informed by a combination of Gemini data, 7,8 wind tunnel testing 9 and CFD. Advances in CFD now allow the unsteady forces on the structure and optics to be computed directly, as a function of external wind speed, orientation of the telescope with respect to the wind, and with enclosure vents either open or closed.…”

Section: Introductionmentioning

confidence: 99%

Unsteady wind loads for TMT: replacing parametric models with CFD

MacMartin

Vogiatzis

2014

SPIE Proceedings

View full text Add to dashboard Cite

Unsteady wind loads due to turbulence inside the telescope enclosure result in image jitter and higher-order image degradation due to M1 segment motion. Advances in computational fluid dynamics (CFD) allow unsteady simulations of the flow around realistic telescope geometry, in order to compute the unsteady forces due to wind turbulence. These simulations can then be used to understand the characteristics of the wind loads. Previous estimates used a parametric model based on a number of assumptions about the wind characteristics, such as a von Karman spectrum and frozen-flow turbulence across M1, and relied on CFD only to estimate parameters such as mean wind speed and turbulent kinetic energy. Using the CFD-computed forces avoids the need for assumptions regarding the flow.We discuss here both the loads on the telescope that lead to image jitter, and the spatially-varying force distribution across the primary mirror, using simulations with the Thirty Meter Telescope (TMT) geometry. The amplitude, temporal spectrum, and spatial distribution of wind disturbances are all estimated; these are then used to compute the resulting image motion and degradation. There are several key differences relative to our earlier parametric model. First, the TMT enclosure provides sufficient wind reduction at the top end (near M2) to render the larger cross-sectional structural areas further inside the enclosure (including M1) significant in determining the overall image jitter. Second, the temporal spectrum is not von Karman as the turbulence is not fully developed; this applies both in predicting image jitter and M1 segment motion. And third, for loads on M1, the spatial characteristics are not consistent with propagating a frozen-flow turbulence screen across the mirror: Frozen flow would result in a relationship between temporal frequency content and spatial frequency content that does not hold in the CFD predictions.Incorporating the new estimates of wind load characteristics into TMT response predictions leads to revised estimates of the response of TMT to wind turbulence, and validates the aerodynamic design of the enclosure.

show abstract

Servo-fluid-elastic modeling of contactless levitated adaptive secondary mirrors

2011

View full text Add to dashboard Cite

The paper develops a comprehensive approach for the servo-fluid-elastic modeling of electromagnetically levitated secondary adaptive mirrors. The system modeling includes the mirror structural dynamics model, its interaction with the fluid film interposed between the mirror and its reference backplate and disturbances due to local air turbulence. The accuracy of the proposed fluid dynamic model is assessed by comparing it with a significant sample of high fidelity 3D Navier-Stokes analyses. The simulation tool is then used to demonstrate the effectiveness and robustness of a recently proposed control, based on a system dynamics cancellation and an iterated steady state feedforward contribution. The simulations clearly highlights the improvements achievable implementing the new control scheme.

show abstract

Buffeting of large telescopes: Wind-tunnel measurements of the flow inside a generic enclosure

Cited by 8 publications

References 19 publications

Wind loads on ground-based telescopes

Wind loads on ground-based telescopes

Unsteady wind loads for TMT: replacing parametric models with CFD

Servo-fluid-elastic modeling of contactless levitated adaptive secondary mirrors

Contact Info

Product

Resources

About