Project of an “Aeroterrace”

Pedro Miguel Leal Lacãopedro.lacao@tecnico.ulisboa.pt

Instituto Superior Técnico, Lisboa, Portugal

June 2015

Abstract

The catering industry is a very unstable activity sector. Besides food, the restaurant’s areaconditions are particularly valued. This project aims to develop simple applications to increasethe comfort levels in the terrace of one particular seafront restaurant. The discomfort factors wereidentified. Two propeller wind-vane anemometers were built to measure the local meteorologicalconditions. A four hole pressure probe was also developed to allow experimental measurements on ascale model. A triangular vertical awning was projected to put at the terrace’s entrance that alloweda wind speed reduction in the meal areas up to 67%. The terrace’s windows’ configurations werechanged in three different ways to reduce both the visual obstructions and the wind velocity coming tothe inside. One of the proposed solutions allows a 85% difference between the speed of the incomingflow and the wind speed inside the terrace. Also, a program was developed to calculate the shadowprojection area at the terrace for different configurations of the shadow devices.Keywords: Wind Speed, Visual Obstructions, Shadow, Anemometers, Pressure Probe

1. Problem Definition and ContextIn general, companies of all sectors try to apply dif-ferentiation strategies in their products or servicesto gain market share. In the restoration businessthis also applies. The strategy is then to offer theclients the best levels of satisfaction in service andcomfort. Some restaurants, bars or cafés are builtin some specially pleasant locations due to the locallandscape like gardens, seafront sites, well planedurban areas and so on. This is a big differentiatingfactor relative to other businesses and tends to beharnessed by building outdoor spaces, like terracesand seating areas. However, local weather condi-tions, namely strong winds, may lead to a poor de-sign of said outdoor spaces. The most common ex-

Figure 1: Example of a poor design of an outdoorspace of a restaurant with the meal area “caged” ina glass structure.

ample of such bad designs are the outdoor spaces“caged” in glass structures like the one presentedon figure 1. The aim of these structures is to avoidincoming wind but the spaces tend to loose the out-door feel. Also, other negative factors arise in theoverall experience of the costumers in such balconiesor terraces. The visual experience is compromised,the temperatures generated inside can become un-comfortable and the costumers may feel a sensationof confinement.

The proposed problem is to develop a set of sim-ple solutions to the structure of a restaurant’s ter-race to improve costumers’ experience. The restau-rant is called Pesca no Prato and is a seafront placelocated at the São Martinho do Porto’s bay, fig-

Figure 2: Geographic location of the restaurantPesca no Prato in São Martinho do Porto’s bay.

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ure 2. The terrace configuration, figure 3, was pro-jected to allow the costumers to enjoy the sea view,protecting them from the wind as much as possi-ble. Unfortunately, the space fails to do both ina complete way. The open entrance in the mid-dle of the terrace turns out to be a means of windflow from outside to the meal areas and the glassstructures alongside the facades act as visual ob-structions to the exterior landscape. The glassesin the windows also contribute to a sense of enclo-sure in an already small space. This terrace, asit is, can present the disadvantages referred abovefor the badly designed outdoor spaces and improve-ments are possible. However, the purpose is not tocompletely redesign the terrace but to make smalladjustments or to add simple aerodynamic appen-dices that fulfill the objectives.

Figure 3: Terrace of the restaurant Pesca no Prato.

The main sources of discomfort identified arethe wind circulating inside the terrace that flowsthrough the open door, the visual obstructions tothe outside and the incident sunshine. The windspeed, beside other factors, is known to have animportant role on human comfort in outside urbanareas, [6] and [5]. The wind can also be unpleasantdue to its effect on the table accessories like nap-kins, cloths, beverages’ cans, etc. The visual ob-structions, window’s glasses at eye level, partiallyblock the view, compromising the visual experienceand contribute to a sense of confinement. Finally,the sunshine levels and contrasts can be, at times,a great source of discomfort, [1]. The terrace isequipped with shadow devices throughout its sur-roundings (figure 3) but, because these devices canonly be extended in the vertical direction, their usecan seriously block the view to the exterior land-scape and increase the confinement sensation. Theaim of the project is to increase the global sensa-tion of comfort inside the terrace, acting on theseidentified parameters.

To approach the identified problems in therestaurant’s terrace three types of solutions are pro-

posed. One is the introduction of a vertical awningat the doorway of the terrace to reduce the winddirected to the meal areas. Other solution is thechanging of the window’s glasses configurations, re-ducing their height and hence reducing the visualobstructions (without compromising the other as-pects of comfort). The last solution is to considerthe effects of other types of shadow devices, notby studying them extensively but to provide therestaurant’s owner tools to do so.

To evaluate the local atmospheric conditionsand their effects inside the terrace two propellerwind-vane anemometers were built and taken tothe restaurant to make measurements. Theseanemometers, as the name suggests, are constitutedby one propeller system with its axis of rotation inthe horizontal position and aligned parallel to thewind by means of a wind-vane. The World Meteoro-logical Organization (WMO) defines the wind as aflow with three dimensional behavior with randomfluctuations of small scale superimposed on a big-ger scale organized flow, [8]. The WMO also refersthat in weather evaluations is common to considerthe wind as a two dimensional vector with hori-zontal speed and direction. The propeller wind-vane anemometers are thus adequate to this pur-pose. Cup anemometers coupled with a vane couldalso have been used but the uncertainty in the windspeed assessment in these instruments is larger com-pared with the propeller systems, [8]. These twoanemometer types also have a linear relation be-tween the rotor angular speed and the horizontalwind speed.

The development of solutions and their assess-ment were made in laboratory on a 1 : 30 scalemodel of the restaurant’s terrace. The atmosphericwind conditions were simulated in wind tunnel test-ings.

On a first approach the flow evaluation was madeusing visualization techniques with wool yarn. Anintroduction of smoke to enable a better judgmentof the flow patterns was tried without success. Al-though the wool yarn had made possible the formu-lation of some conclusions, a quantitative assess-ment was needed. Considering that the objectiveis to make changes to model’s terrace’s configu-ration and evaluate their impact, only a point bypoint, probe intrusive, flow measurement techniquecould allow such evaluation. Both hot-wire andpressure probe techniques fit the desired require-ments. However, hot-wire multidimensional probetips are expensive, very delicate and may be toolarge for the measurements to be taken. Due tothe robust construction, versatility and experimen-tal operation simplicity, multi-hole pressure probesare the instruments to use.

Multi-hole pressure probes are instruments that

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extend the principles of operation of the conven-tional pitot tubes by introducing more pressure in-takes on the probe tip. There are several types ofmulti-hole pressure probes distinguished by differ-ent tip geometries, number of pressure intakes, cali-bration and data reduction methods but they are al-most all considerably limited in angular acceptance.An overview on multi-hole pressure probes is pre-sented in [7]. The flow inside the terrace is verycomplex and is difficult, or even impossible, to esti-mate the local flow direction. The direction of theflow in one specific point in space inside the terracecan vary significantly when changes are made toits structure. Is then critical to use one instrumentwith a broad angular range. There are probes calledomnidirectional probes that have 12 or 18 pressureintakes that can measure three dimensional flowswith an angular acceptance cone up to ±160o. Intheory, these instruments would be the best suitedfor the required application but they’re very expen-sive and, once again, the probe tips could be largerthan ideal. With these considerations and takinginto account the directional limitations of the ma-jority of the pressure probes available,it was chosento develop from scratch a four hole pressure probethat could overcome said limitations, thus allowingthe needed experimental measurements.

2. InstrumentationFor the analysis on this work were built two types ofinstruments, the propeller wind-vane anemometersto assess the meteorological conditions surroundingthe restaurant’s terrace and the four hole pressureprobe to perform the experimental analysis of theproposed solutions on a scale model. This chap-ter refers to the development and characteristics ofthese instruments.

2.1. Propeller Wind-Vane AnemometersThe instruments developed were projected to ac-quire the wind speed and the wind directions sep-arately with the data recorded raw. This indepen-dence of systems allows that one of them can stillrun even when the other, for some reason, can’t.This characteristic is extremely useful because, infield work, the anemometers can be subject to roughconditions and become damaged. There were builttwo anemometers, each one with one speed acqui-sition system, one direction acquisition system andone data recording system. The anemometers de-veloped are similar in every aspect and one of themis presented in figure 4.

The speed acquisition sensor is a propeller at-tached to a dc motor. The dc motor runs as a gen-erator and gives the signal output information. Thechoice of a dc motor was due to the linear relationbetween the motor rotational speed and the voltageat its terminals. The direction acquisition system

Figure 4: One of the propeller wind-vane anemome-ters developed and built for the project.

is a wind-vane connected to a potentiometer thatis the signal generator of the system. The poten-tiometer is useful because of its linear relations andthe type used on the instruments has an angularregulation limit of 270o, which is a restriction ofthe system. The speed and the directional systemsare connected to an Arduino Uno board that, inconjunction with an ITead SD Card Shield boardand a SD card, records the voltages read by thesensors. The system is powered by 9V batteries.Alternatively, the Arduino Uno can be connectedto a personal computer and the data can be storedthere directly.

The anemometers were calibrated at a wind tun-nel. The calibration process consist in discrete vari-ations of speed or angle according to the systembeing considered with the respective record of theoutput signal. After, the recorded data is processedand a relation between the instruments’ signals andthe flow parameters is stipulated. As expected, theresponse of the sensors was linear. Naturally, theanemometers have operational limits. Some lim-its are inherent to the instruments’ characteristics

Speed Sensor Wind SpeedLower reading limit 2.3 m/sUpper reading limit 10.0 m/s

Wind-Vane Response Wind SpeedBeginning of a response 2.7 m/sVisible vibrations 3.0 m/sPositioning with low accuracy(±20o to ±30o)

3.0 m/s

Positioning with medium ac-curacy (±10o)

3.5 m/s

Accurate positioning 3.8 m/s

Table 1: Summary of some basic dynamic responsecharacteristics of the developed anemometers.

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and others are due to calibration definitions. Forinstance, the upper speed reading limit in bothanemometers is 10 m/s. This value was set bychoice, since it represents a threshold to near galeconditions. On the other hand, the lower speedreading limit is an intrinsic limitation of the instru-ments. Table 1 presents some important values ofthe dynamic response of the instruments.

2.2. Four Hole Pressure ProbeThe difficulties in predicting the flow direction in-side the scale model of the restaurant’s terrace andthe angular limitations of the majority of the multi-hole pressure probes available led do the design anddevelopment of a pressure probe that made the nec-essary measurements possible.

The typical cylindrical three hole pressure probeconfiguration, figure 5, allows flow measurementswithin a planar angular range of ±70o, [2].

Figure 5: Configuration of a three hole pressureprobe. Pressure intakes represented by the num-bers 1,2 and 3. Source: reference [7].

The proposed design consist in the introductionof an extra pressure intake to the three hole config-uration. All the pressure intakes are on the sameplane and are spaced 90o from each others, figures6 and 7. The probe is designed to measure two di-mensional flows with 360o angular acceptance andis meant to be inserted perpendicularly to the flow.

Figure 6: Four hole pressure probe body and tip.

Figure 7: Four hole pressure probe intakes arrange-ment. Illustration of a transversal cut at the probetip.

The pressure is read in differential form betweenpressure intakes on opposite sides by means of twodifferential pressure transducers, one for each pres-sure difference. V1,2 is the voltage reading from thequantity p1 − p2 and V3,4 the reading from p3 − p4(see figure 7). The pressure transducers used are theHoneywell DC002NDC4 pressure sensors and thedata acquisition is done by a NI USB-6008 modulethrough a connection to a computer.

The probe was calibrated at the wind tunnel ona system developed for that purpose. The calibra-tion consists on the immersion of the probe in aflow to relate the measured pressures with the ve-locity vector. Several exposures with different flowspeeds and probe positions are needed. The probesensors’ outputs (V1,2 and V3,4) depend strongly onflow speed (U) and incidence angle (α). Figure 8presents the output voltages’ behavior for one fixedflow speed and variable incidence angle. α is con-sidered zero when the flow falls along the pressuretaps 1-2 and varies according to the direction shownin figure 7.

0 45 90 135 180 225 270 315 3600.0

1.0

2.0

3.0

4.0

α

Voltagem

(V)

V1,2V3,4

Figure 8: Voltage readings as a function of the flowincidence angle α for a fixed flow speed (16.6m/s).

The values of V1,2 e V3,4 are out of phase by90o, as expected from the pressure taps’ arrange-

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ments. The maximum and minimum values corre-spond to the situation where the stagnation pointson the probe coincide with the pressure taps. Tounderstand this pressure variation is fundamentalto know the pressure distribution around a cylin-der, figure 9. In the figure θ represents the anglebetween each point in the cylinder surface and thefree stream direction.

Figure 9: Pressure coefficient Cp distributionaround a cylinder for laminar, turbulent and invis-cid flow. Source: reference [2].

For fluid flows around a cylinder, the pressureis maximum for θ = 0, the stagnation point, anddecreases to a minimum (numerical values are de-pendent on Reynolds number). For further θ an-gles there is an adverse pressure gradient and theboundary layer separates at some point, dependingon flow regime. This point is about θ = 82o forlaminar flow and θ = 120o for turbulent flow.

It can be noticed that the flow around the de-signed probe tip has a similar behavior. However,because the probe readings are pressure differencesbetween intakes at opposite sides, there are someconsiderations to make. In each reading there’s onepressure that dominates the measured quantity atfirst and the pressure variation resembles the oneson figure 9. From a certain angle the pressure fromthe opposite tap assumes importance. For exam-ple, in V1,2, for the flow velocity shown in figure8, the pressure in tap 1 dominates until the inci-dence angle (α) is somewhere around 90o. Then,the pressure in tap 2 starts to overpass the one intap 1 and the pressure variation develops converselybut somewhat in the same way. The pressure dis-tribution around the probe tip is symmetrical, factthat is reflected in the shown plot.

The calibration files give the probe outputs asfunctions of the flow velocity and angle. To com-pute the desired velocity and angle from voltagemeasurements is necessary to invert that relations.In the literature are presented several methods todo this for a wide range of pressure probe typesand number of pressure intakes. References [2] and[7] are two examples. However, most of the meth-ods are limited in angle range (as the ones cited).Due to the pressure distribution in the 360o accep-

Figure 10: Calibration map on the (V1,2, V3,4) plane(calibration points connected merely in a represen-tative way).

tance angle, the variables relations are not bijectiveand inverting the system is no easy task. The plotfrom figure 8 illustrates this statement relatively tothe incidence angle. To overcome this problem wasdeveloped a linear interpolation method and a cali-bration map on the (V1,2, V3,4) plane was set, figure10. The voltage calibration points correspondent toconsecutive velocities and angles are properly con-nected into triangular elements. The data process-ing methodology consists in locating the measuredvoltage pair in the elements of the calibration mapand interpolate for speed and direction.

The division of the calibration map into triangu-lar elements is preferable compared with the divi-sion into quadrilaterals (bilinear interpolation) forthe sake of consistency and robustness. Triangularelements are always possible to form. Quadrilat-erals suitable for interpolation, on the other hand,aren’t. When connecting the calibrations points ofconsecutive velocities and angles into quadrilateralssome odd shapes can be formed, precluding inter-polation. The method used is also universal in theway that the triangular elements can be applica-ble for every calibration map introduced for thisprobe, with more or less points considered in thecalibration process. With bilinear interpolation, thegreater the number of points in the calibration map,the greater the oddly shaped elements formed.

The triangular elements formed in the proposedmethod have irregular shapes and a coordinatetransformation to a fixed geometry is necessary.The fixed geometry element is called master ele-ment and is represented on the transformed planewith coordinates (ξ,η). Figure 11 portrays an ar-bitrary triangular element and the master elementcorrespondent to the coordinate transformation ofthe first. Equations 1 and 2 represent this coor-dinate transformation, where V3,4,a, V3,4,b, V3,4,c,V1,2,a, V1,2,b and V1,2,c are the calibration coordi-nates of the points of the element in consideration.

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ab

c

Ωe

V3,4

V1,2

(a)

η = 1

ξ = 1

a b

c

∧Ω

ξ

η

(b)

Figure 11: (a): Arbitrary triangular element on the(V3,4, V1,2) plane. (b): Master triangular elementcorrespondent to the coordinate transformation ofthe element in (a).

From these equations is possible to identify in whichelement of the calibration map do the measured V1,2and V3,4 voltages fit. For that, equations 1 and 2need to be solved simultaneously for ξ and η fromthe voltages read by the probe and the requirementsin 3 need to be satisfied.

V3,4 = V3,4,a + (V3,4,b − V3,4,a)ξ +

+ (V3,4,c − V3,4,a)η(1)

V1,2 = V1,2,a + (V1,2,b − V1,2,a)ξ +

+ (V1,2,c − V1,2,a)η(2)

η ≤ −ξ + 1 ξ ≥ 0 η ≥ 0 (3)

If the conditions in 3 are true, the measured volt-ages correspond to the element being tested and theresultant ξ,η values are used to compute the flow ve-locity and angle by the relations 4 e 5, respectively.

U = Ua + (Ub − Ua)ξ + (Uc − Ua)η (4)

α = αa + (αb − αa)ξ + (αc − αa)η (5)

To evaluate the overall data acquisition and pro-cessing uncertainty of the developed method adataset was collected. The absolute error (for speedand direction) was defined as the largest difference

Absolute ErrorVelocity ±0.4 (m/s) Angle ±17.4o

Table 2: Overall absolute error in the assessment ofthe velocity U and angle α by the pressure probe.

between the measured values and the real ones. Theerror values are presented on table 2.

Some voltage pairs (V1,2, V3,4) find correspon-dence with more than one triangular element onthe calibration map, although only one relates totrue conditions. Sometimes it’s possible to distin-guish the real solution by knowing some informationabout the flow beforehand (for example: having anestimate on flow direction). Other times it’s not.Despite this fact does not prevent the use of theprobe, it’s a considerable limitation of the instru-ment.

3. Proposed Solutions, Results and Discus-sion

As introduced on chapter 1, are proposed threetypes of solutions that address the identified dis-comfort factors. The development of an awning toreduce the wind that comes into the terrace, chang-ing the configuration of the windows’ glasses to re-duce the visual obstructions and the development ofa computational tool to evaluate the shadow effectsof the shadow devices.

First, an assessment of the atmospheric flow en-vironment is made using the propeller wind-vaneanemometers.

The evaluation of the proposed solutions wasdone in wind tunnel experiments with a scale model.The four hole pressure probe developed was used inthe measurements. For this, it is assumed that theflow in the terrace develops in horizontal planes andcan be defined by a speed modulus and a direction.

3.1. Atmospheric Flow EnvironmentThe restaurant’s frontal facade is directed to south-east as it can be seen in figure 12.

Figure 12: Pesca no Prato’s terrace orientation.

The anemometers were taken to the restaurantand several measurements were made at some cho-

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0 2 4 6 80

1

2

3

4

5

6

7

Time (min)

Uv

(m/s)

Uv P3θv P3Uv P2θv P2Uv P4-h1Uv P4-h2

Figure 13: Wind speed (Uv) and direction (θv) at the acquisition points P2 and P3 and mean wind speedat P4-h1 and P4-h2. ↓ – wind from north; ↑ – wind from south; ← – wind from east; → – wind fromwest. Measurements taken at 21/06/2014.

sen locations. Figure 14 shows some of the acquisi-tion locations at the terrace surroundings.

Figure 14: Top view of the terrace with dimensionsin cm. Acquisition data points at the terrace sur-roundings.

The most important results found with this anal-ysis are presented on figure 13. The measurementsshown refer to the acquisition points P2, P3 eP4. In point P4, data is recorded for two differ-ent heights, h1=2.24m and h2=2.55m, both abovelateral glasses’ height. Because the wind speed inP4 measurements was too low, only a mean value ispresented. The wind in the measurements shown inthe plot has a direction tangent to the terrace. Inthat situation, the wind hardly enters the terrace,surrounding it instead. The wind speed measuredinside the terrace (P4) is much lower than outside(P2 and P3), even at the considered heights (mea-surements above window’s glasses).

These results are very important because they al-low us to conclude that lateral winds do not affectthe activity inside the terrace very much. Conse-quently, the problematic wind directions must be

those from south to southeast. The data presentedalso confirms, indirectly, that the terrace’s opendoorway is the critical site to the inlet of wind. Indesigning an awning to reduce the wind that comesinto the terrace, the doorway must be the locationto put it.

3.2. Wind ProblemThe solution proposed to improve the comfort con-ditions related to the wind inside the terrace is theintroduction of a vertical awning at its entrance.The awning is the triangular sail-like device shownin figure 15. The shape was chosen to fit the nau-tical theme of both restaurant and region, becauseit’s a simple form for a real prototype developmentand because it doesn’t obstruct the view so much ateye level. The awning can be mounted at the twosides of the entrance and can be fixed at any pointin the ground so that its effect can be availed ac-cording to wind direction. The awning’s dimensionsare restricted by urban planning policies.

Figure 15: Vertical awning’s prototype mounted atthe terrace’s entrance.

The studies with wool yarn on the scale modelshow good indications of the effect produced by theawning. In the situation without the awning, figure

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(a)

(b)

Figure 16: Wool yarn visualization technique. Topview of the scale model. Experiments with U∞ =10 m/s and incidence angle of 30o relative to thefrontal facade. (a): Without awning. (b): Awningat the left side of the entrance with inclination of30o to the right side.

16(a), the wind comes through the doorway directlyto the meal areas (yellow delimited region). Withthe awning, figure 16(b), the direction of the windat the entrance is changed completely. The entranceis now a wind exit location, allowing foresee that themeal areas are not so prominently whipped by it.

0 2 4 6 8 10 12 14 16 180.0

0.5

1.0

1.5

2.0

2.5

3.0

U (m/s)

h(m

)

U∞Without Awning

Awning at 30o

Figure 17: Wind speed (U) along terrace’s height(h) at meal location. The awning position is thesame as in the situation of figure 16.

To quantify the effects produced by the awning, astudy at a point inside the yellow delimited region(figure 16) was made using the four hole pressureprobe in a vertical scan. The conditions are exactlythe same as for the wool yarn visualization exper-iments (details in figure’s caption), except for thefree stream flow speed U∞. The results for windspeed are presented on figure 17 (direction is omit-ted). Analyzing the figure is possible to concludethat the awning is able to reduce the wind speedinside the terrace up to 67% at the levels of torsoand head of an adult in a seated position. The re-sults suggest that the comfort levels at the mealareas are improved with the implemented solutiondue to the considerably high wind speed reductionat the heights representative of the restaurant’s ac-tivity. This conclusions hold for the meal area atthe other side of the terrace since this is a symmet-ric problem.

3.3. Visual ObstructionsTo reduce the visual obstructions three new configu-rations for the glasses in the windows are proposed.Figures 3 and 15 help visualizing the solutions whendescribed. The lateral windows don’t give visual ac-cess to any special environment, making the frontwindows the main focus for an intervention. One so-lution is to place the front glasses at an angle of 45o

to the outside, reducing the effective glass height in10 cm (test 1). This is a very simple configurationand only involves changing the fitting of the glassesat the windows. Other solution to be considered isexactly the same as the first one but with an actualreduction in the glass height, resulting in an effec-tive height reduction of about 25 cm (test 2). Inthis solution, beside the fitting in the windows, theglasses also need to be changed. The last configura-tion proposed is to explore a cavity effect, removingthe front glasses completely but closing the lateralsides in glass up to the top. This solution is alsoof very simple implementation, only requiring theacquisition of properly sized glasses for the lateralwindows.

The experimental tests for the solutions proposedhere were carried out considering the most unfa-vorable conditions to the problem, which are thefrontal wind conditions. The measurements weremade with the pressure probe in vertical scans at apoint immediately behind one of the front windows.

Figure 18 compares the results for the configura-tions of test 1, test 2 and present situation. Thedata shows that is possible to reduce the front glassheight without compromising the comfort levels dueto wind effects. Further, is possible to ascertainsome level of improvements in wind speed condi-tions inside the terrace with values that can be aslow as half of the ones for present conditions at

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0 2 4 6 8 10 12 14 16 180.0

0.5

1.0

1.5

2.0

2.5

3.0

U (m/s)

h(m

)U∞

PresentTest 1Test 2

Figure 18: Wind speed (U) along terrace’s height(h) at a location immediately behind one of the win-dows. Free stream flow U∞ = 16.6 m/s with 0o

incidence angle (frontal incidence).

head and torso levels. Test 1 measurements indi-cate bigger wind speed values for the lower heightswhich can be bad for human comfort. However, thisevaluation can only be made with user experience.Overall, the results are encouraging and in favor ofthe proposed solutions.

The results for the cavity effect configuration arepresented on figure 19 in a comparison with thepresent situation. The conditions for this experi-ment are the same as for the other tests with visualobstructions. It is immediately recognizable thatthe closure of the side windows has a very positiveimpact on wind reduction inside the terrace. Thewind speed inside is much smaller (can be up to fourtimes smaller) than in the present configuration ofthe windows throughout the vertical dimension of

0 2 4 6 8 10 12 14 16 180.0

0.5

1.0

1.5

2.0

2.5

3.0

U |x,y (m/s)

h(m

)

U∞Present

Cavity Effect

Figure 19: Wind speed (U) along terrace’s height(h) at a location immediately behind one of the win-dows. Free stream flow U∞ = 16.6 m/s with 0o

incidence angle (frontal incidence).

the terrace. From the presented solutions this isthe only one that can induce an uniform reductionin the wind entering the terrace along its verticaldimension. Also, the wind velocity inside the ter-race can be 85% smaller than the free stream atmo-spheric flow, which is a very large reduction. Thissolution is a very promising one because it allowsto remove entirely the visual obstructions in thefrontal facade of the terrace, which was the mainobjective of the study in this section, accomplish-ing at the same time a large reduction of the windentering the space. In this way the levels of comfortare improved in two different areas, the comfort re-lated with wind levels and the comfort related withthe visual experience.

3.4. Sunshine ProblemThe shadow devices installed at the terrace sur-roundings are not optimal because, as they can onlymove in the vertical direction, they can become vi-sual obstructions and can contribute to a sense ofconfinement. The same shadow effects could be ac-complished if the shadow devices could be openedat an angle to the exterior in a properly designedsystem. The systems to be considered depend onthe amount that the restaurant’s owner is willingto invest. In this way, it was chosen to develop asimple program that allows the restaurant’s ownerto assess the effects of determined configurations ofthe shadow devices at any given day of the year andtime of the day. If the shadow devices are not tobe changed, the program serves as a complemen-tary tool in evaluating the best configuration of thepresent devices.

As an example of the program capabilities a casestudy is presented where two situation are com-pared. In one situation is considered the installedshadow devices lowered 0.5m (C1) and in the otheris considered that the devices can be extended atan angle of 40o to the exterior and lowered 0.65m(C2). In both situations the vertical projections ofthe extended shadow devices are the same. In otherwords, the visual obstructions are similar. The cal-culations were made to show a shadow projectionon a horizontal plane at 1m height (height that cov-ers at least the heads and shoulders of adults in aseated position) and are illustrated in figure 20. Itis possible to conclude that configuration C2 is bet-ter than the present one, not only allowing a biggershadow projection but also contributing to a lessenclosed space. The program allows drawing con-clusions of the type shown in this case study, givingthe owner and the other restaurant’s staff the hintsfor informed decisions.

4. ConclusionsThe project developed in this work is an engineeringproblem. From a starting point broadly defined, the

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(a) (b)

Figure 20: Shadow projection on a horizontal plane at 1m height at the restaurant’s terrace for two hoursof the first of July. Top view of the terrace. C1 - Shadow devices installed at present and lowered 0.5m.C2 - Consideration of shadow devices open at a 40o angle to the exterior and lowered 0.65m.

main problematic aspects were identified. Thesewere the wind entering the restaurant’s terrace, thevisual obstructions to the outside landscape and thesunshine intensity. A set of solutions was proposedthat addressed specifically these problems.

To evaluate the proposed solutions there werebuilt two different instruments, the propeller wind-vane anemometers and the four hole pressure probe.The anemometers provided good information aboutthe local atmospheric conditions, contributing tothe definition of the main source of wind in therestaurant’s terrace. The four hole pressure probeallowed experimental assessments that no other in-strument could do. Despite some limitations in itsuse, the probe was essential in quantifying the ef-fects of the proposed solutions.

An awning was developed to be fixed verticallyat the terrace’s door to deflect the incident wind.The experimental results revealed the benefits ofthe sail placed at the defined position with a windspeed reduction up to 67% at human torso and headlevels.

In order to reduce the visual obstructions weresuggested three options. The first two (glasses inthe windows with an angle of 45o and differentheights) don’t imply major changes to the presentconfiguration of the terrace. Besides the reductionof visual obstructions, a reduction in wind enter-ing through the windows was also achieved. The fi-nal configuration explores a called cavity effect thatshows excellent results by allowing the removal ofthe front windows’ glasses and greatly reducing thewind entering through that same windows (up tofour times in a comparison with the terrace in itspresent state).

Finally, a computational tool was developed tohelp the restaurant’s owner and staff in their evalua-tion of the sunshine conditions inside the terrace ac-cording to the shadow devices’ configurations con-sidered by them.

The ideas presented here are also applicable to

other exterior structures.

References[1] R. Compagnon and J. Goyette-Pernot. Visual

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