Estimation of Wind Energy Over Roof of C Buildings Faculty of Engineering University of Riau

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1 November 23, 215 Estimation of Wind Energy Over Roof of C Bildings Faclty of Engineering University of Ria Iwan Krniawan, a,* a) Departement of Mechanical Engineering, Universitas Ria, Pekanbar, 28293, Indonesia *Corresponding athor: iwan.ktm@gmail.com Paper History Received: 1-October-215 Received in revised form: 2-November-215 Accepted: 23-Nevember-215 ABSTRACT Bilding-integrated rban wind trbines are promising low-cost renewable energy devices. However, the take-p of rban wind trbines in high density sbrban environments is still very interesting to investigate by isses sch as: a) low wind speeds; b) high trblence intensity; and c) the perception of potentially high levels of aerodynamic noise generated by the trbines. This paper presents a nmerical stdy was performed to C bilding Faclty of Engineering University of Ria sing type of RANS trblence k-e models in the open sorce code Open FOAM, and the reslts are compared with pblished in-sit measrements and pblished wind tnnel tests. Based on the comptational reslts, site for wind trbine installation above these roofs has been assessed. It has been fond that trblence intensity and wind direction for monting wind trbine site is 1.8H in the corner location above roof C bilding. KEY WORDS: k-e, Open FOAM, RANS, Urban Wind trbine. NOMENCLATURE API Δ Δ American Petrolem Institte Temperatre Difference in and ot Thermal Expansion Anchor Length Expansion Pressre Force Friction Force Design Compressive Strain Critical Strain 1. INTRODUCTION Bilding-integrated rban wind trbines is one of the potentially low-cost renewable sorces of energy. Despite their potential, Ledo et al. [7] pointed ot that the reasons behind the limited installation of micro-wind trbines in rban areas are the low mean wind speeds, high levels of trblence and relatively high aerodynamic noise levels generated by the trbines. If a trbine is sited in the wrong location on a dwelling roof, it is possible for the power otpt to diminish to zero for significant periods of time, evenwhen the wind is blowing strongly. Another reason for the catios integration of micro-wind trbines within rban areas is the negative reptation of rban wind energy de to the erroneos installations of rooftop wind systems as a signal of spport for sstainability withot adeqate consideration of safety, strctral bilding integrity or trbine performance. Ths, nmerical modelling of the wind flow above the bilding roof is important for the design of residential sbrban landscapes. It is expected that more and more hoses with integrated wind trbines will be bilt as sstainability becomes an increasing design driver for new hoses in the ftre [5]. Toa-Silva et al [11] and abohela et al [1] present a review of the opportnities and challenges of rban wind energy that stresses the necessity to perform accrate analyses of the flow behavior on bilding roofs, in order to get more information abot possible positions of wind trbines to take advantage of the accelerating effect of the wind above the bilding, the adeqate kind of trbine and the estimation of the power generation. Ledo et al. [7] stdied wind flow arond pitched, pyramidal and flat roofs nder three wind directions (, 45& 9 o ) for the prpose of roof monting wind trbines, they conclded that the power density above the flat roof is greater and more consistent than above the other roof types and they recommended extending the investigation to inclde other roof shapes. Phillips et al. [1] 78 Pblished by International Society of Ocean, Mechanical and Aerospace Scientists and Engineers

2 November 23, 215 investigated the monting location for a single winddirection for a gabled roof and recommended extending the investigation to inclde more roof types and more locations with different wind directions. Mertens [8] analysed flow over a flatroof with a view to developing a small wind trbine siting gide lines focssing on the monting height. In the present work, local wind flow characteristics above C bilding in Faclty of Engineering University of Ria is considered, figre 1 Potential power wind investigated by employing Comptational Flid Dynamics (CFD) to installation location of roof monted wind trbines. Figre 1: Camps faclty of Engineering University of Ria 2. NUMERICAL ANALYSIS For modelling wind flow over complex terrain, the Reynoldsaveraged Navier-Stokes approach (RANS) combined with a k- epsilon k-ε scheme as trblence model, is the most common approach in wind engineering. The method provides a fair compromise between comptational costs and accracy. Reynolds decomposition is employed to the variables of the governing eqations, whereby each variable is divided into a time-averaged part and a flctating part, = +, reslting in the two following eqations: P ρ + = + ρ g + µ + ρ x i i i i i t x xi x x xi x k k = C bilding The terms i as the Reynolds stresses and physically represent the additional stresses de to the flctating components of the flow. These Reynolds stresses have been modelled according to a Bossinesq approximation, shown in Eq. (3), an analogy of Newton s friction law: (1) (2) τ ρ i 2 i i µ = = t + + k i xi xi 3 ρ δ where µ t is the trblent viscosity and k 1/ 2 i (3) = is the trblent kinetic energy (TKE). The standard k-epsilon (k-ε) model, based on a two-eqation trblent energy scheme provides reasonable reslts in approximately netral atmospheric conditions, and provides an acceptable estimate of the trblence intensity throgh the trblent kinetic energy term. For example, some best practice gide lines conclde that the k ε standard model shold not be sed in simlations for wind engineering problems, and recommend the improved twoeqation models or differential stress models [5,12]. However, some other researchers fond that the k ε standard model maybe better, Wang et al [13]fond that the k ε standard model gives rather better performance than the realizable k ε, Reynolds stress models (RSM) or renormalization grop (RNG) k ε Inflow Wind Profile The velocity profile at the inlet bondary of the simlation domain mst be accrately modelled to provide valid reslts of wind simlation in the bilt environment. The roghness of the grond affects the profile of wind velocity,, and therefore is necessary to be part of velocity profile simlation. The following eqation is sed to model the wind profile at the inlet of CFD domain[ : * z + z = ln κ z (4) *2 k = (5) Cµ ε = κ *3 ( z + z ) where is the inlet velocity (horizontal, of axis x) at height z, * is the friction velocity, κ is the von Karman constant, z is the aerodynamics roghness length and C μ is the trblence model constant. The comparison between thewind profile and the analytic inlet vales is given in figre. 1. z (m) CFD (m/s) Analytic Figre 2: Inlet velocity comparison between analytic and CFD simlation in thevertical section (6) 79 Pblished by International Society of Ocean, Mechanical and Aerospace Scientists and Engineers

3 November 23, Description of the case stdy and simlation details Strctred hexahedral mesh, shown in Fig. 2. A mesh independence stdy was carried ot to determine the dependence of the flow field on the refinement of the mesh. Final mesh statistics in the present models were: 7473 elements for case degree, case 9 degree and for case 18 degree. The bilding models with 15 m height, 15.6 m wide and oter radis 45 m are placed in a rectanglar domain for back side models and C shape for front models. Dimensions comptational domain are X xy x Z = 1 x 15 x 1 m 3.The inlet velocity profile was specified by eq.4-6 (Blocken et al) The downstream bondary was specified as opening with zero relative pressre. The side faces were setas symmetric bondaryand top of the domain were set as wall slip condition. All solid bondaries bottom and C bilding were set as no-slip walls. Standard trblent k-ε (TKE) sed in comptational. 3. RESULT AND DISCUSSION Figre 3: Type and density mesh sed in comptational CFD simlation, as a wind assessment tool, is embedded with errors and ncertainties. H [4] attribted this to the many physical and nmerical variables which might pzzle even experienced sers. Ths, Blocken et al. [3] asserted the importance of validating CFD simlations against other wind assessment tools. In this section wind flow arond a srface C bilding in a trblent channel flow is investigated sing the in hose CFD code Open FOAM. For validation prposes the reslts will be compared to pblished in-sit measrements and pblished wind tnnel tests. (A) (A) (B) (B) (C) Figre 4: Comptational domain with each orientations (A) degree, (B) 9 degree and (C) 18 degree (C) Figre 5: Comparison of the trblent kinetic energy (m 2 /s 2 ) at vertical section at the centre of the domain. (A) Drbin-Standard, (B) k-ε standard case A, (C) Exp. Tominagaet all (28). (note : comparison only trend profile k not vale).(toa et all:11) 3.1 Wind Flow above Bilding C Wind flow above the roofs is complex and cannot be predicted from the wind data becase of the proximity of the roofs in densely poplated sbrban residential hoses, the flow is highly trblent and the wind velocity field isvery different from the free stream velocity de to the blff body effects of the bildings and the evoltion of separated regions. It is therefore important that local wind characteristics sch as the flow pattern, trblence intensity and wind velocity need to be careflly analyzed when micro-trbines are to be integrated within these bilt environments. 8 Pblished by International Society of Ocean, Mechanical and Aerospace Scientists and Engineers

4 November 23, 215 deg 9 deg z (m) above C bilding degree 9 degree Trblence Intensity Figre 8: Trblence Intensity for three different inflow to corner location 18 deg Figre 6: Flow pattern velocity for three orientation wind inflow 3.2 Flow pattern In this section the flow patterns above the C bilding of the threedifferent inflow Fig. 6 showsfor degree, 9 degree and 18 degree. According to figre 6, notanywhere above the Cblding roof is sitable sitefor installing a trbine, onlythe corner position is recommended as a monting location. Trblence intensity affects the operability and the lifetime ofwind trbines. Ledoet all, a trbine shold not beexposed to wind with trblence intensity greater than 16-18%.Therefore, it is important to estimate the trblence intensity atany prospective trbine monting location. In this stdy three winddirections, a degree, 9 degree and 18 degree were considered. The reslts for the, 9, 18 degree for z above roof C bilding, trblence intensity level decrease with height. Figre 8, trblence intensity level for < 18 % at 1.8H. In figre 7 & 8, Data trblence intensity and velocity are mean vale at three location to corner location above C bilding. Three location are x, y and z vale shows for table 1 : Table 1: Three location for x, y and z vale data for and trblence intensity. degre 9 degree 18 degree point x y z x y z x y z point Point point Point point Point 2 z (m) above C bilding 18 degree 9 degree degree (m/s) Figre 7: Velocity for different inflow to corner location -3, -2, 15 Plane x, y -3, -3, 15-2, -3, 15-1, -3, 15-1, -4, 15 Figre 9: Estimation location monting rban wind trbines on the roof C bilding 81 Pblished by International Society of Ocean, Mechanical and Aerospace Scientists and Engineers

5 November 23, Wind velocity reslt In the previos section, favorable monting location for windtrbine has been identified based on the level of trblenceintensity are 1.7H. For wind direction, it is observed an increase of wind velocity in all inflow orientation. Wind power density (Eq. (7& 8)) is a sefl way to evalate maximm thewind power available at a potential site. 3 Power Density =.5ρ (7) ref % power density = x1 (8) % power density above roof ef Figre 1: potential power density as fnction of wind direction It can be sed to compare the power available above the three wind direction above roof C bilding. The dependence of the power density on the winddirection for a trbine located at the corner of the c bilding. Maximm increase power density is 1.8H, a location for monting wind trbine is shown in Fig. 9 and 1. In all cases, the wind trbine hb is 27 m above c bilding at corner location (tabel 1). 4. CONCLUSION degree 9 degree 18 degree z (m) In this investigation, CFD simlations of the wind flow arond asingle bilding were performed within hose code openfoam sing k-ε RANS trblence models, and the reslts were compared with pblished in-sit measrements and pblished wind tnnel tests. Wind flow simlations above C bilding with wind direction have been performed. The simlations looked into the wind flow characteristics in terms of trblence intensity, wind velocity and wind flow pattern. Based on the comptational reslts, site for wind trbine installation above these roofs has been assessed. It has been fond that trblence intensity and wind direction for monting wind trbine site for 1.8Hin the corner location above roof C bilding according to table 1 data. Frther stdy of the wind flow characteristics with the trbinemonted on the roof will also need to be carried ot. In this case,modelling sing LES might be sed to stdy the nsteady wind flowpattern and to evalate the feasibility of a roof trbine installationbased on the annal wind power density. Feasibility rban wind trbines farm need to investigate above C bilding. ACKNOWLEDGEMENTS The athors wold like to convey a great appreciation to lembagapenelitiandanpengabdian (LPPM-UR) niversity Of Ria for spporting this research. REFERENCE 1. Abohela, I., Hamza, N., Ddek, S., (213). Effect of roof shape, wind direction, bilding height and rban configration on the energy yield and positioning of roof monted wind trbines. Renew. Energy vol.5, pp Blocken B, Stathopolos T, Carmeliet J, (27). CFD simlation of the atmospheric bondary layer: wall fnction problems. Atmospheric Environment Vol. 41 pp Blocken B, Stathopolos T, Carmeliet J, Hensen JLM,(211). Application of comptational flid dynamics in bilding performance simlation for the otdoor environment: an overview. Jornal of Bilding Performance Simlation. Vol4 pp H C-H. (23). Proposed gidelines of sing CFD and the validity of the CFD models in the nmerical simlations of wind environments arond bildings. In: School of the bilt environment. Edinbrgh: Heriot-Watt University;. p J. Franke, C. Hirsch, A.G. Jensen, H.W. Krüs, M. Schatzmann, P.S. Westbry, S.D.Miles, J.A. Wisse, N.G. Wright, (24). Recommendations on the se of CFD in wind engineering, in: J.P.A.J. van Beeck (Ed.), Proc. Int. Conf. Urban Wind Engineering and Bilding Aerodynamics. COST Action C14, Impact of Wind and Storm on City Life Bilt Environment, 5 7 May, von Karman Institte, Sint-Genesis- Rode, Belgim,. 6. J. Hang, Z.W. Lo, M. Sandberg, J. Gong, (213). Natral ventilation assessment in typical open and semi-open rban environments nder varios wind directions, Bild.Environ. Vol.7 pp Ledo, L., Kosasih, P.B., Cooper, P., (211). Roof monting site analysis for micro-wind trbines. Renew. Energy vol.36, pp Mertens S. (23). The energy yield of roof monted wind trbines. Wind Engineering. vol. 27, pp Peacock AD, Jenkins D, Ahadzi M, Berry A, Tran S. (28). Micro wind trbines in the UK domestic sector. Wind Energy and Bildings, vol. 4,pp Phillips R.(27) Micro-wind trbines in rban environments: an assessment. Bracknell: IHS BRE Press for BRE Trst. 11. Toa-Silva, F.,Carlos Peralta, Oscar Lopez-Garcia, Jorge Navarro.(215). Roof region dependent wind potential assessment with different RANS trblence models.j. of wind Eng. And Ind. Aerodyn.vol.142, pp Tominaga, Y., Mochida, A., Mrakami, S., Sawaki, S., (28). Comparison of varios revised it k ϵ models and LES applied to flow arond a high-rise bilding model with 1:1:2 82 Pblished by International Society of Ocean, Mechanical and Aerospace Scientists and Engineers

6 November 23, 215 shape placed within the srface bondary layer. J. Wind Eng.Ind. Aerodyn. Vol,96. pp Wang, B, L.D. Cot, L Adolphe, S. Geoffroy, J. Morchain. (215). Estimation Of Wind Energy Over Roof Of Two Perpendiclar Bildings. Energy an d Bilding. Vol. 88, pp Y. Tominaga, A. Mochida, R. Yoshie, H. Kataoka, T. Noz, M. Yoshikawa, T. Shirasawa, (28). AIJ gidelines for practical applications of CFD to pedestrian wind environment arond bildings, J. Wind Eng. Ind. Aerodyn. 96 (1 11) Pblished by International Society of Ocean, Mechanical and Aerospace Scientists and Engineers