wind tunnel investigation of the wind environment of the

UniServices Reference: 36727.001

Wind Tunnel Investigation of the Wind Environment of the Proposed Auckland Waterfront Apartments in Auckland

23 February 2018

Prepared for: Auckland Waterfront Apartments Ltd. c/- Chris Minty Pacific Advisory and Management Limited PO Box 106596 Auckland Auckland, 1143

Prepared by: Dr Yin Fai Li The Wind Engineering Group 70 Symonds St c/- The University of Auckland, Private Bag 92019, Victoria St West, Auckland 1142, New Zealand

Wind Engineering Group The University of Auckland

II

Executive Summary

Background UniServices was approached for evaluating the wind effects of the proposed Auckland Waterfront Apartments at W3 and W4 Wynyard Quarter in Auckland. The focus of this study is to investigate its effect on the wind environment of the surrounding public pedestrian areas.

Procedure Wind tunnel tests were performed on a 1:200 scale model of the proposed Auckland Waterfront Apartment in Auckland. The tests measured the pedestrian wind environment around the proposed development with the surroundings modelled in detail for a radius of about 350 m centred at the target development.

The wind tunnel tests consisted of investigations of pedestrian level wind speeds using the so-called “Irwin probe” surface wind sensor. The results of the wind tunnel tests were combined with long term Auckland Meteorological data to predict the percentage of time that various wind speeds are likely to be exceeded in the vicinity of the proposed development. The resulting data were used to put the areas into Auckland Unitary Plan wind categories.

Conclusions The wind environment in the vicinity of Proposed Auckland Waterfront Apartment has been studied in the wind tunnel.

The wind tunnel tests and subsequent analysis showed that:

1. All tested locations are rated safe. 2. Most of the tested locations have a wind comfort category of B, which is

suitable for short term recreation and relaxation. 3. The wind condition within the central courtyard (location 5, 6 and 15) is

category A, which is suitable for longer term recreation and relaxation. 4. The windiest location of the site is Location 21 with a category C, which is

at the intersection of Daldy Street and Gaunt Street. It is affected significantly by both north-easterly and south-westerly winds.


III

Table of Contents

Executive Summary .................................................................................. II

Table of Contents ..................................................................................... III

Introduction ......................................................................................... 1

Test Procedure ..................................................................................... 2

Results and Discussion .......................................................................... 3

Conclusions and Recommendations ......................................................... 4

References .......................................................................................... 5

Tables ...................................................................................................... 6

Figures ..................................................................................................... 8

Appendix A Wind Field Modelling ............................................................. 11

Appendix B Wind Tunnel and Models ........................................................ 13

Appendix C Instrumentation and Measurements ........................................ 18

Appendix D Data Analysis ....................................................................... 19

Appendix E Wind Environment of the Existing Site ..................................... 20


1

Introduction

BECA, on behalf of Auckland Waterfront Apartments Ltd, approached Dr Yin Fai Li of the Mechanical Engineering Department, the University of Auckland (“University”) to request a fee proposal for a wind engineering study on the proposed Auckland Waterfront Apartments development at W3 & W4 Wynyard Quarter, Auckland. After an initial wind opinion assessment was conducted a wind tunnel test was requested.

The Auckland Waterfront Apartments development is located at W3 and W4 of Wynyard Quarter, Auckland. The development consists of five buildings that vary in height between 7 to 12 storeys, a central podium courtyard, and terrace housing. There is a central east-west laneway which runs between the apartment buildings, and also entrances to the courtyard from the north and south directions.

Figure 1 shows the 3D view of the proposal development


2

Test Procedure

2.1 Wind Field Modelling Details of the wind field modelling can be found in Appendix A.

2.2 Wind tunnel and models Details of wind tunnel and the wind tunnel models can be found in Appendix B.

2.3 Instrumentation and Measurements Technical details of the instrumentations and sampling parameters used in the test are described in Appendix C.

2.4 Data Analysis Technical details of the data analysis methodologies are described in Appendix D.


3

Results and Discussion

The region studied in the present investigation is the roadways and footpaths on Beaumont Street, Pakenham Street, Daldy Street and Gaunt Street, and the public area within the development. Table 1 shows the wind performance categories from the Auckland City Council[1] which is widely used to assess the pedestrian wind comfort for developments around Auckland.

3.1 Clause H.8.6.28(1)(a) Figure 2 shows the wind performance category for the proposed site as defined in clause H.8.6.28(1)(a) of AUP-OIP.

Table 2 shows the expected number of hours in a year that a mean wind speed of 6m/s is exceeded for each location.

The result shows that most of the tested locations scored a comfort category B, which is suitable for short term recreation or relaxation. The generally benign wind conditions around the site can be attributed to sheltering by neighbouring buildings as well as extensive coverage of canopies on footpaths.

Within the central courtyard (location 5, 6 and 15) are some of the calmest area within the site with a comfort category A, which is suitable for longer term recreation and relaxation.

The test data shows that Location 21 is the windiest location within the site, which is rated at the top end of comfort category C similar to a previous study [2]. This location is significantly affected by both the north-easterly winds from 60° and 90° and the south-westerly winds from 210° and 240°. This is unique in a sense that all other tested locations are only affected by winds from one of these prevailing wind sectors.

It is unlikely that further canopy protection will mitigate the current windy conditions at location 21. It is believed that localised porous screens, dense soft landscape such as shrubs and hedges may be able to provide the necessary relief. Chamfering, rounding, or recessing of the building corner at the intersection of Daldy Street and Gaunt Street may reduce the wind acceleration by providing a “softer” path for the wind to flow around the building

3.2 Clause H.8.6.28(1)(b) Figure 3 shows the wind safety performance assessed against clause H.8.6.28(1)(b) of AUP-OIP. All tested locations are rated safe.


4

Conclusions and Recommendations

The wind environment in the vicinity of proposed Auckland Waterfront Apartment has been studied in the wind tunnel.

The wind tunnel tests and subsequent analysis showed that:

1. All tested locations are rated safe. 2. Most of the tested locations have a wind comfort category of B, which is

suitable for short term recreation and relaxation. 3. The wind condition within the central courtyard (location 5, 6 and 15) is

category A, which is suitable for longer term recreation and relaxation. 4. The windiest location of the site is at Location 21 with a Category C,

which is at the intersection of Daldy Street and Gaunt Street. It is affected significantly by both north-easterly and south-westerly winds.


5

References

1. Auckland unitary plan Operative In Part, in Auckland unitary plan. 2016, Auckland Council: Auckland, N.Z.

2. Le Pelley, D.J., Wind Tunnel Investigation Of The Pedestrian Level Wind Environment In The Vicinity Of The W3 And W4 Developments In Wynyard Quarter, Auckland, Auckland UniServices Ltd report no. 34622.001, 2015

3. Structural design actions : AS/NZS 1170 (SET) : (Parts 0, 1, 2, 3 & 5), AS/NZS 1170.2-2011

4. Irwin, H.P.A.H., A simple omnidirectional sensor for wind-tunnel studies of pedestrian-level winds. Journal of Wind Engineering & Industrial Aerodynamics, 1981. 7(3): p. 219-239.

5. Halkyard, R., et al., Digital filter adaptation for tubing response correction at reduced sampling frequencies. Journal of Wind Engineering & Industrial Aerodynamics, 2010. 98(12): p. 833-842.


6

Tables

Table 1 Performance Category, from Table H8.6.28.1 of the AUP-OIP

Performance Category

Description

A Areas of pedestrian use containing significant formal elements and features intended to encourage longer term recreational or relaxation use, such as major and minor public squares, parks and other open spaces, including. Aotea Square, Queen Elizabeth Square, Albert Park, Myers Park, St Patrick’s Square, and Freyberg Place

B Areas of pedestrian use containing minor elements and features intended to encourage short-term recreation or relaxation, such as minor pedestrian open spaces, pleasance areas in road reserves, streets with significant groupings of landscaped seating features, including Khartoum Place, Mayoral Drive pleasance areas, and Queen Street

C Areas of formed footpath or open space pedestrian linkages, used primarily for pedestrian transit and devoid of significant or repeated recreational or relaxational features, such as footpaths where not covered in categories A or B above

D Areas of road, carriage way, or vehicular routes, used primarily for vehicular transit and open storage, such as roads generally where devoid of any features or form which would include the spaces in categories A - C above

E Represents conditions which are dangerous to the elderly and infants and of considerable cumulative discomfort to others. Category E conditions are unacceptable and are not allocated to any physically defined areas of the city


7

Table 2 Hours per year for which a wind speed of 6m/s is exceeded

Location Hours per year 1 406 2 16 3 0 4 96 5 2 6 0 7 87 8 19 9 9

10 46 11 2 12 23 13 24 14 18 15 1 16 64 17 42 18 57 19 54 20 36 21 596 22 89 23 80 24 5 25 27 26 185 27 49


8

Figures

Figure 1 3D view of the proposed development


9

Figure 2 Wind performance category of the proposed site assessed against H8.6.28(1)(a) of AUP-OIP


10

Figure 3 Safety rating of the proposed site assessed against H8.6.28(1)(b) of AUP-OIP


11

Appendix A Wind Field Modelling

A.1 Terrain and Wind Tunnel Setup Based on the current Australasian Wind Loading Standard ASNZS 1170-2011.2[3], the upwind terrains for the target site is terrain category 3 for all wind directions.

In order to correctly model the characteristics of the approaching winds, such as turbulence intensity and velocity profiles, in the wind tunnel, a combination of roughness blocks, square posts, stripping fence and spires were placed in the upwind section of the wind tunnel. Figure A.1 shows the comparison between the measured wind profiles and the full scale target profiles.

Figure A.1 Mean velocity and turbulence intensity profile for the wind tunnel test


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A.2 Wind Frequency The wind frequency data for the Auckland region used in the current study are shown in Figure A.2.

Wind Rose for Auckland, at a height of 200 m

Percent time wind speed exceeds that stated, per 10 degree interval

0 1 2 3 4 5 6

0 10 20

30 40

50 60

70 80

90 100

110 120

130 140

150 160 170

180 190 200

210 220

230 240

250 260 270

280 290

300 310

320 330

340 350

P(>0, m/s), % P(>5, m/s), % P(>10, m/s), %

Figure A.2 Wind Frequency for Auckland, reference to 200m height


13

Appendix B Wind Tunnel and Models

B.1 Wind Tunnel The wind tunnel test for the current study was conducted in the closed circuit wind tunnel of the Mechanical Engineering Department of the University of Auckland in the Ray Meyer Building at the Newmarket Campus. With a test section of 3.6m wide by 2.5m high and a top speed in excess of 20m/s, this new wind tunnel facility is the largest wind tunnel in New Zealand and has special instrumentation for undertaking investigations of pedestrian flows around buildings, pressures on and vibrations of buildings, aerodynamic drag and power of elite cyclists, aerodynamic forces and pressures on model race cars like the FSAE cars built by Mechanical students, as well as many other aerodynamic studies.

Figure B.1 and B.2 shows the outside and the test section of the closed-circuit wind tunnel.

Figure B.1: The boundary layer wind tunnel


14

Figure B.2: The test section of the boundary layer wind tunnel, with the model of Auckland city on the turntable.

B.2 Wind tunnel Models The surround model of ~3.4m diameter in model scale, or ~350m radius in full scale was included in this wind tunnel study. The surround model was constructed using high quality foam and MDF according to information obtained from public domain and purposely conducted site visits.

The target model was built with details according to the drawing supplied by RTA Studio and Barker & Associates as follows:

Drawing items Date received 170817 AWA RTA and JX Combined Model_v2016_updated B3.3ds 16th November 2017

A16314_200_revC.PDF 27th November 2017 A16314_201_revC.PDF 27th November 2017

Photographs of the target and surrounds model were sent to the design team for review on 15th February 2018 ahead of the wind tunnel test.

Trees and soft landscaping details are incorporated into the test model in accordance with the supplied drawings.

Figure B.3 shows the close up view of the surrounds and the target model. Figures B.4 and B.5 show the wind tunnel model. Figures B.6 shows close up view of trees.


15

Figure B.3 Close up view of the wind tunnel model viewed from southwest, showing trees on Beaumont Street and Gaunt Street.


16

Figure B.4 Wind tunnel model from northwest, showing trees on Pakenham Street and neighbouring buildings.

Figure B.5 Wind tunnel model, viewed from downwind.


17

Figure B.6 Close up view of the trees in the wind tunnel model


18

Appendix C Instrumentation and Measurements

C.1 Electronically Scanned Pressure System Pressure measurement was done using an electronically scanned pressure system developed in house in the Department of Mechanical Engineering, the University of Auckland. The system allows up to 512 channels of pressures to be sampled simultaneously at high speeds in order to capture rapid fluctuation of the signals. The pressure transducers within the system (Honeywell differential pressure transducer XSCL04DC) has a time response of 1ms.

C.2 Wind Speed Sensor A set of 27 so-called “Irwin probe” pressure based omnidirectional wind speed sensors similar to that described in [4] are used to simultaneously measure local wind speed at different locations on the model.

C.3 Sampling Considerations The frequency response of the instrumentation was determined on the basis of equivalence of reduced velocity in prototype as in model. In addition the Australasian Wind Engineering Society recommends that the sampling period is between 10 minutes to several hours in full scale. The reduced velocity is given by:

m fs

fs fsm

m fs m

UT UTL L

or

T LUT U L

=

=

.

In the present instance the model scale Lfs/Lm is 200, if the wind tunnel speed is set at ~50% of the full scale wind speed for the 1 year return period, a 60 second data acquisition time at 400 Hz in the wind tunnel will be equivalent to a 100 minutes data acquisition at 4 Hz. The wind tunnel test was therefore performed at ~50% of the full scale wind speeds


19

Appendix D Data Analysis

D.1 Tubing Response Corrections Fluctuating pressures measured through long tubes are subjected to distortion by what commonly known as “organ pipe” effect, which certain frequency get amplified and attenuated depend on the geometry of the long tube such as its length and bore.

The measured data of this study were digitally corrected by applying a recursive filter as described in reference [5], with the characteristic of this filter purposely trained to correct for the distortion caused by this specific tube length.

D.2 Wind Speed Ratios Pressure measurements from the Irwin probes, after correcting for tubing response, are combined to form the differential pressure time histories. These time histories are then converted to omnidirectional mean and gust wind speed based on [4], expressed as a ratio to a reference mean wind speed, for each probe location for each wind direction.

D.3 Local Wind Statistics The wind speed ratios are then combined with the wind frequency statistics for the region as shown in appendix A.2, transposed to the reference height at site location taking account of the effect of terrain roughness in a direction-by-direction base, in order to derive a non-directional wind probability distribution to each probe location, suitable for direct comparison with wind comfort and safety criteria applicable to the region to determine the comfort and safety performance for each investigated location.


20

Appendix E Wind Environment of the Existing Site

Wind tunnel test has been performed in order to ascertain the wind environment for the current site condition.

E.1 Clause H.8.6.28(1)(a) Figure E.1 shows the wind comfort rating of the existing site assessed against H8.6.28(1)(a) of AUP-OIP.

Figure E.1 Wind performance category of the existing site assessed against H8.6.28(1)(a) of AUP-OIP


21

E.2 Clause H.8.6.28(1)(b) Figure E.2 shows the safety rating of the existing site assessed against H8.6.28(1)(b) of AUP-OIP.

Figure E.2 Safety rating of the existing site assessed against H8.6.28(1)(b) of AUP-OIP

The Wind Engineering Group 70 Symonds St

c/- The University of Auckland, Private Bag 92019, Victoria St West,

Auckland 1142, New Zealand

18 June 2018

Auckland Waterfront Apartment Ltd 124 Halsey Street Attn: Tony McKee

Hi Tony,

Re: Change of building geometry

With reference to the new elevation drawings and the presentation slides issued to us from BECA on 14th June 2018, it appears that the external envelope has not changed significantly from the geometry tested on February 2018 in our wind tunnel. The extra floor on B1 may change the wind flow but since the wind environment for that part of the site is mainly calm, I do not think the conclusion of the report will change although it may cause small changes in the level of wind comfort in the vicinity, i.e., some locations on the northwest side of the site will move closer to the upper end of its current wind category while some move towards the lower end. The critical location in the previous test was location 21, at the corner of Gaunt Street and Daldy Street, and it current at the upper end of category C. The wind tunnel results have shown that it is mainly impacted by the southwesterly and northeasterly winds, blowing over B6 and Wynyard Common respectively. Since B6 has not changed significantly it is my opinion that it will remain at the upper end of Category C. Other minor changes in details, such as the shape of balconies, are not likely to affect the ground level wind environment to any significant extent. Regards, Dr Yin Fai Li Mechanical Engineering Department

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