DAPPLE - Wind Tunnel ModellingH. Cheng and A. Robins

University of Surrey

Low resolution model (1:200)Experimental set-upQuality assurance for experimentsMean concentration measurementsPuff releasesConclusions and future work

Low resolution model

• Model scale: 1:200• Flat roof• Height refers to the building eaves• Street block is modelled as rectangular block• Model mean height: 22m (110mm)• Model co-ordinates

Experimental set-up

• Tunnel test section: 4000x700x300m (20x3.5x1.5 m)• Neutral BL without considering traffic simulation• Model mounted on turntable• Uref=2.5 m/s, south-westerly wind (45˚)• Instrumentation: FID and FFID• Source located in York St. • ID=1.2m(6mm) for mean concentration• ID=2.3m (11.5mm) for instantaneous concentration• Ground level concentration

Quality assurance

• Repeatability• Source flow-rate effects (3-10 l/min)• Reference wind speed effects• Frequency response for FFID• Behaviour of solenoid valve (for short duration emissions)

Mean concentration measurements

• Source locations (road side and road centre)• Receptors: down wind region• Detailed intersection measurements• Non-dimensional concentration, C* = CUrefH2/Q

• Upper bound to whole data set:

CUref/Q = 50R-2

not dependent on building height, H

Data from one experiment

Data from two experiments

Data from all experiments

Range from about 50 to 500m

Short-duration releases

• 10s duration pulses (travel, rise and decay time scales)

• Variable puff duration (0.5 to 4s)

Characteristic time scales

Measured time scales

Puff - single realisation and ensemble average

Conclusions

Plumes: C*max 1/R2

Significant variations across streetsPuffs: Uadvection ≈ 0.13 Uref ≈ UH/4

Peak/Mean ≈ 3.5 - 4

Future work: • detailed mapping of flow and concentration fields• flux exchange at intersection• exchanges with flow above roof level• effects of modelling detail

Detail near intersection