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Wind Tunnel Modelling in Conservation

Stanislav Pospíšil, Miloš Drdácký, Zuzana Slížková, Jaroslav Lesák, Dagmar Knotková

Institute of Theoretical and Applied Mechanics, AS CR

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1 Introduction and motivation

1

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• Several wind tunnels available but only few combine more effects -> CWT

• Mostly designated to automotive industry

• For buildings and urban zones -> athmospheric WT

• CWT Nantes (CSTB) - 1990, aerod. characteristics of full scale supercritical Reynolds numbers – real, large scale physical simulation

2 Current status

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CLIMATIC WIND TUNNEL

2 Current status – CWT, BLWT

• rain-250 mm/h•sand conc. - 10 g/m3 in a 10 m2 section• -25 °C to +50 °C and relative humidity from 30% to 100%•flow speed can be set from 90 km/h to 140 km/h. • snow mantle (15 cm/h) on the 200 m2 floor of the test chamber.

BL WIND TUNNEL

• flow speed from 0 km/h to 140 km/h. • visualization

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3 Gothic sandstone pinnacles subjected to a combined climatic load

• Gothic pinnacles from one of the most important late medieval Gothic churches, St. Barbara’s in Kutná Hora (Bohemia), were exposed to accelerated clima for a period of four days in order to test the efficiency of hydrophobic surface coating

• Usually individual effects are analysed

• CWT based research - unique opportunity for the analyse the behaviour of historic materials subjected to combined climatic loads

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Influence of the wind direction on the deterioration of valuable architectural detail

Real structure

Complex shape

3 Gothic sandstone pinnacles subjected to a combined climatic load

St. Barbara catedral

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3 Gothic sandstone pinnacles subjected to a combined climatic load

Loading of the specimen by low and high temperature cycles

Weighting of the specimens

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3 Gothic sandstone pinnacles subjected to a combined climatic load

Thermocamera analysis

higher temperature scan

lower temperature scan

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3 Gothic sandstone pinnacles subjected to a combined climatic load

• Temperature changes are very sensitive to the shape of details of complex architectural forms. • Cooling and evaporation are highly influenced by the wind flow, especially cold wind flow.• Driven rain increases the water penetration into the stone only at the beginning •A hydrophobic surface coating protects the stone very well, if applied compactly on a sufficiently large area of interest. product. •Our technique can be advantageously applied for studying the air flow and eddies around complex shapes and forms.

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Corrosion due to particles deposition- wind analysis is important Plan view of the building

and soiling sensors placement

3 Corrosion due to weather and air pollution

CZ National MUSEUM

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Wind tunnel analysis

Dust deposition –1. optical

determination-big costly effort

2. fine weighting procedure

New adhesive samplers has been used with success.

3 Corrosion due to weather and air pollution

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3 Corrosion due to weather and air pollution

•There has been no unambiguous relation between the deposition degree on the samplers at the models with differrent scales

•More experiments are needed in order to understand scale factors and similitude between the prototype and models.

•The spectrofotometric method has been used with good results

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• use of numerical calculation need to be confronted with experiments• laser sheet fluid visualization

Pressure taps on several levels

3 Wind and wind driven rain damage to historical objects

Benchmark objects

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3 Wind and wind driven rain damage to historical objects

• virtual wind tunnel with appropriate numerical model can give qualitatively reliable results

RMS pressures patternsnum

exp

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4 Conclusions

• Three examples demonstrating the exposure of HO to wind and combined load were presented

• There is evident need of experimental facility for the multidimensional science like heritage conservation

• The use of CWT can create the link between individual researches and therefore focus on synergetic effects