This is an author-deposited version published in: https://sam.ensam.eu Handle ID: .http://hdl.handle.net/10985/14916
To cite this version :
Malo LE GUELLEC, Yann AMICE - Sailing site investigation through CFD modelling of micrometeorology - In: The Third International Conference on Innovation in High Performance Sailing Yachts, INNOVSAIL, Lorient, France, France, 2013-06 - The Third International Conference on Innovation in High Performance Sailing Yachts, Lorient, France - 2013
Any correspondence concerning this service should be sent to the repository Administrator : archiveouverte@ensam.eu
The Third International Conference on Innovation in High Performance Sailing Yachts, Lorient, France
26
TH– 28
THJune, 2013
SAILING SITE INVESTIGATION THROUGH CFD MODELLING OF
MICROMETEOROLOGY
M. Le Guellec,Fluidyn FRANCE, France, malo.leguellec@fluidyn.com
Y.Amice,DépartementMétéorologie - Institut de Recherche de l’ÉcoleNavale, France, yann.amice@gmail.com; To have a prior accurate knowledge of the local wind currents on a water body is of crucial importance for the performance of the sailing team. In the recent years, Computational Fluid Dynamics (CFD) has proven itself a powerful tool in atmospheric modelling. By solving the Navier-Stokes equations and with correct description of the atmospheric boundary layer and turbulence at the domain boundaries, the local influences of the shore topography and the obstacles on the wind flows can be investigated in detail. Two examples of the use of CFD (Fluidyn PANWIND software) are presented here. The first one shows the coastal wind analysis of 2012 Olympic sailing site of Weymouth, UK. The local wind effects due to the harbour and hill have been determined and compared to observations of wind velocity and direction for several wind conditions.The second example required to model the wind over the training base of the French Sailing Teamin Brest, France. This landlocked bay, surrounded by two steep hills and linked to the Atlantic Ocean by a strait, emphasizes the need for a CFD simulation of the wind which provided the patterns of wind around the racing areacompared with empirical observations.
NOMENCLATURE
C1 k-εturbulence model constant
C2 k-εturbulence model constant
CS dimensionless turbulence production factor
CE dimensionless turbulence viscosity constant for the k-ε model
Cp specific heat of air (J g-1 K-1)
Fg/p force due to: (g) gravitational acceleration, (p) interaction with droplets/particles (N m-2)
g gravitational acceleration (9.8 m s-2)
G turbulence production rate by shear = σ∇u (m2
s-3)
hm specific enthalpy of species m (J kg-1)
I specific internal energy (J kg-1)
J heat flux vector (W m-2)
k turbulent kinetic energy per unit mass (m2 s-2)
kc thermal conductivity (W m-1 K-1)
L Monin-Obukhov turbulent length scale (m) Qh rate of specific internal energy gain due to (h)
surface energy budget (J kg-1 s-1)
Ri Richardson number, dimensionless
t time since the start of the release (s)
T temperature (K)
u fluid velocity (m s-1)
u* surface friction velocity (m s-1)
v wind speed (m s-1)
Wp Turbulence production due to interaction with particles (m2 s-3)
z height (m)
z0 ground roughness length(m) Greek letters
ρ density of air
µ primary (shear) viscosity of fluid (kg m−1 s−1)
λ secondary (bulk) viscosity of fluid (kg m−1 s−1)
σ Newtonian viscous stress tensor (N m-2)
ε dissipation of turbulent kinetic energy (m2 s-3)
ζ Monin-Obukhov similarity variable = z/L, dimensionless
κ Von Karman constant = 0.41, dimensionless θ potential temperature (K)
θ* temperature scale
σh turbulent Prandtl number, dimensionless
σk dimensionless turbulence model constant for the k equation
σε dimensionless turbulence model constant for the
ε equation Ψ1/2(ς) similarity profiles
1 INTRO Accurate w direction an sailing com sailing is measureme characterise short, and Furthermor mass consi from the p donot provi of interest. The atmos particularly terrain. The land and roughness s modify larg be evaluate The comple need for a The wind f speed and w In many wi breeze effe local weath focuses on predefined and conside Two differe frame of thi Weymouth, 2012 Olym competition Weymouth south of th area, there i topography flow can be The secon knownroad of France ( characterist assess t topography two very s Atlantic Oc orientation. The wind m the Quelern Armorique DUCTION wind field d nd turbulence mpetitions. Th between 2.5 ent data obtai
e fully the flo d only defin
re the interpol istent techniqu point measure
ide the require spheric circul y dependent o e topography sea (estuar surface (urban ge scale flow d in details. ex topography complete 3D flow modelling wind direction ind studies, th ect based on her station me n the local wind bounda ering topograp ent interesting is project. , a coastal ci mpic Sailing E
n spots are sho is a city surr he city, i.e., in is a hilly islan y is complex a e very difficul nd sailing ar stead (bay) of (see Figure 2 tic of this wa the impact y.Indeed, it is a steep hills (50 cean by a strai . modelling foc n Peninsula (2 (3rd sub-doma description(wi e) plays an i he proper win 5-18 m/s. T ned are usua ow, as data ti ned at a sp lation wind fl ues which ex ements(meteor ed accuracy o lation in the on local effect , the transitio ries, bays,… n areas, forests ws and these in y in coastal ar D CFD simula g provides the ns around the r he objective is the statistics asurements. T wind charac ary condition
phical and rou g areas have b ity in Souther Events in Au own in Figure rounded by se n the south-e nd named Port and consequen t to comprehe rea is locate f Brest, in Fin ). It is requir ater body int t of th a landlocked b 0 to 80 m) a it about 2 km cuses here on 2nd sub-domai ain) ind speed, w mportant role d speed range Traditional in ally insufficien
ime series are pecific locat flow models u xtrapolate the rological stati ver the entire e lower layer ts due to com on zones betw …), the diffe s…), contribu nfluences hav rea emphasize ation of the w e patterns of w racing area. s toanalyse the s of synoptic This paper ma cteristics wit assumed con ughness effect been studied in rn UK hosted ugust. The sa e 1. ea and hills. In east of the sa tland (130m). ntly the local w end. ed in the w nistère departm red to identify to details to he surroun bay surrounde and linked to m wide with a two mains a in) and theCap
wind e for e for n-situ nt to e too ions. using data ions) area rs is mplex ween ferent ute to ve to s the wind. wind e sea and ainly th a nstant . n the d the ailing n the ailing The wind well-ment y the fully nding ed by o the 240° areas: pe of 2 2 F f w l t t s m o I f w T m
26
TH– 28
Figure 1 Figure 2 2WIND FLO 2.1 FLUIDYN Fluidyn-PAN family which wind flows ar large scale by the topograph the local m solves the Na momentum co on structured In this code fluid density i where is the The momentu mixture is8
THJune, 20
: Schematic m Wey 2: Area of inte OW MODELI N-PANWIND WIND is a m allows a quic round buildin y taking into a hy, the influen meteorological avier-Stokes e onservation) wor unstructure the mass con is expressed a
e gradient of th um conserva
013
map for sailing ymouth erests in Brest ING D module of fluid ck and accura ngs, hills at lo account all kin nce of terrain conditions. equations (Ma with a finite v ed mesh. nservation equ as he considered ation equation g events in roadstead dyn-PANACH atesimulation ocal or mediu nds of obstacle and vegetatio The softwa ass, energy an volume metho uation for tot
d quantity. n for the flu
HE of um es, on, are nd od tal uid
The Third International Conference on Innovation in High Performance Sailing Yachts, Lorient, France
26
TH– 28
THJune, 2013
∂ρ
∂ ∇• ρ σ ∇
where σ is Newtonian viscous stress tensor (σ= µ[∇u+(∇u)T]+λ(∇•u)i,µ, λ = first and second coefficients of viscosity, λ = -2/3µ; T = matrix transpose; i = unit dyadic - product of vectors).
The energy conservation equation is: ∂ρ
∂ ∇• ρ ∇• ρε Where is the specific internal energy, is theheat flux = kc∇.T + ρ∑[hm∇(ρm/ρ)], is the rate of specific internal energy gain due surface energy budget.
2.2 GEOMETRY AND MESH
(a)
(b)
Figure 3: Weymouth unstructured mesh at ground level ((a) full domain (b) nested domain)
For Weymouth case, the topography of the site was collected from Landform Profile Plus data on a global domain of 24 km * 25 km. This data has a 15–25 centimetre root mean square error (RMSE) accuracy and a grid resolution of 2 metres to 10 meters - sufficiently detailed to represent key terrain features. The harbour and jetties were modelled in finer details in an embedded domain of dimensions 5 km * 10 km. The finest cell size of the unstructured mesh in the harbour is 12 m and the averaged size dimension in
the sailing area is 25 m (see figure 3) resulting in a total of 2 million cells. Vertical mesh gets a 2m resolution from ground level to 12m of altitude. The vertical mesh is then coarser till until 200 m high.
A large main domain of 43km by 32km was used for Brest’s Roadstead case. A first nested domain of 30 km*28 km has been defined. Two smaller embedded domains with an area around 80 km² were used in order to evaluate accurately the wind flows as shown in figure 2.The topography was extracted from The NASA Shuttle Radar Topographic Mission (SRTM) who has provided digital elevation data (DEMs) for over 80% of the globe. The SRTM data is available as 3 arc second (approx. 90m resolution) Digital Elevation Model. The finest cell size of the unstructured mesh in the two nested domains is 30m and the averaged size dimension in the sailing area is 50m resulting in a 2.3 million cells. Vertical mesh gets a 3m resolution from ground level to 15m of altitude. The vertical mesh is then coarser until 200 m high.
2.3 TURBULENCE MODEL, BOUNDARY AND INITIAL CONDITIONS
The standard k-ε model has been used throughout the simulations.
The k-ε model is a two-equation linear eddy viscosity model. The PANACHE implementation of this model is derived from the standard high-Re form with corrections for buoyancy and compressibility. It solves the transport equations for turbulent kinetic energy, k, and its dissipation rate, ε. The incompressible versions of the equations are:
( ) ν ν ε σ ∂ + ∇ ⋅ = ∇ ⋅ + ∇ + + − ∂t t l k b k k k k P P U
( )
ε(
)
ε ε ν ε ε ν ε ε ε σ ∂ + ∇ ⋅ = ∇ ⋅ + ∇ + + − ∂t U l t k C1 Pk C Pb b C2where, Pk=
ν γ
t& :
∇
U
, the mechanical production rate of k Pb=ν β
σ
∇
g
t hT
, the buoyancy production rate of k
σk= Prandtl number for turbulent diffusion of k
σε= Prandtl number for turbulent diffusion of ε
µt= turbulent eddy diffusivity
Cs1,Cs2=k-ε turbulence model dimensionless constants
The eddy diffusivity is computed using:
26
TH– 28
THJune, 2013
Ambient mean wind speed and air temperature profiles are specified within the model domain and are represented by logarithmic functions, such that:
κ Ψ ς
θ σ θ
κ Ψ ς
Whereθ* = temperature scale; Ψ ς and Ψ ς = similarity profile.
The surface friction velocity, , the temperature scale θ*, and the Monin-Obukhov length, L are related by: L
= u*2T / (g κθ*)and θ* = Q
h / (ρCp u*).
The micrometeorological parameters , θ*, and L are evaluated for different atmospheric stability classes. They have been evaluated for neutral conditions. In this study, the roughness lengthhas been chosen equal to 0.001m (typical of water body). The roughness length for the land has been chosen equal to 0.4m. 2.4 SIMULATION AND SOLVER PARAMETERS In the frame of this study, the solver is a pressure-based fully implicit segregated method on unstructured meshes. It is well suited for flows that are steady or quasi-unsteady (slowly changing).
It solves all governing equations separately. It uses an iterative procedure for both steady state and transient cases. SIMPLE schemeis used for pressure computation. It uses a formulation valid for flows at all speeds and for any thermodynamic model.
3 RESULTS
3.1 BREST ROADSTEAD CASE ANALYSIS 3.1.1. Climatology
The dominant flux in all seasons comes from west to west-southwest even if a few nuances exist depending on the season. The most significant factor is the south pathwayof the low pressure zone. During winter, stronger west or southwest winds are usually observed and frequent disturbances which impact the Atlantic coast.
During the summer, this scheme remains relevant but strengthening anti-cyclonic depression requires a more northern flow, which allows the Atlantic coast to sample light winds and a more conventional summer time.
The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high (see Figure 4). Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds across the North Atlantic.
Figure 4: The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean - L : Low pressure area in Iceland - H: High pressure area in Azores and Northern Africa
3.1.2. Local effect of terrain on the wind flows
The results of the modelling focus on the wind direction modification due to the topography around the sailing area.
The wind directions areSW (225°) and E(90°) and the simulations were done for a wind speed of 10 m/s at a height of 10m for both directions.
In Figure 5, the white colour arrows and the pink colour contours represent a deviation greater than +15° from the mean direction and the black colour arrowsand the blue colour contours indicate a deviation greater than -15°. All the views are voluntarily schematic for an easy understanding of the wind fields in the area by non-specialist people.
Figure 5: Wind deviation in case of SW conditions The wind flow is channelled through the axis of the strait, exceptwhere a little deviation is observednear the tip of Spanish peninsula Quernel. The flow is divided in a West-Southwest and a South-Southwest part when reaching the peninsula ofPlougastel (see figure 6).
T
The Third I
Figure 6: W 225° - 10 negativ The results show that t area betwee effect of direction. I figure 9). In the str direction. T the sailors i Figure 7: WInternationa
Wind direction m/s(Google E ve deviation a d s for the E cothe wind take en Brest and t the tip of A In this area, rait, the win This is a class
in the area.
Wind deviation
al Conferenc
n contoursfor Earth view) –I and in red colo deviation
ondition (see es a North-Ea
the peninsula o Armorique g
the wind spe nd takes a s sical phenome n in case of E
ce on Innov
a wind condit In blue color t or the positive Figures 7 an st direction in of Plougastel. gives a south eed increases stable North-enon observe conditionsvation in Hig
tion the e nd 8) n the . The heast (see -East d by 3 T m a T T c f T i s wgh Perform
26
TH– 28
Figure 8: Wi 90° - 10 m/s o negative Figure 9: Win 10 m/s– In re m/s and in b 3.2. WEYMO The results of modification area.The wind dire The wind conditions) in figure 1) and i The wind velo in most of the show low win wind direction
mance Sailin
8
THJune, 20
ind direction c on (Google E deviation and dev nd speed cont ed colour, the wblue color, the m OUTH CASE A f the modellin due to the to ections are WS keeps its i n the middle in the middle ocity for the W e zone 1. Nev nd speed in th n is more than
ng Yachts, L
013
contoursfor a w arth view) - In d in red color t viation tours at surfac wind speed in e wind speed i m/s ANALYSIS g focus on the opography aro SW (240° to 2 initial direct of the harb of the bay (zo WSW directio vertheless, the he North of th n 260°.Lorient, Fran
wind conditio n blue color th the positive celevel for 90° n higher then 1 in lower than 4 e wind directio ound the sailin 270°). ion (bounda our (zone 1 one 6). on remains hig e velocity fiel he zone 1 if tnce
on he ° - 10 4 on ng ary in gh lds theIn the zon influence downwind exposed to wind direct Figure 10: Figure 1 conditio negativ 6 CONCL In order modelling sailing team Fluidyn PA presented h analysis of UK. The lo have been d wind veloci The secon training ba France. Th hills and l emphasizes This simula ne 2 (figure of coastal area of hilly various effec tion. Wind deviati 11: Wind dire on (Google Ea ve deviation a d LUSIONS to demonstr for the purp ms, two examp ANWIND de here. The firs f 2012 Olymp ocal wind effe
determined an ity and directi nd example m
ase of the Fr is landlocked linked to the s the need for ation provide 1), there i landforms. y and dispar cts within a fe ion in case of ction or a260° arth view) - In and in red colo deviation
rate the use pose of wind
ples of the us edicated soft st one shows pic sailing si ects due to the nd compared t ion for several modelled the ench Sailing d bay surroun e Atlantic Oc a CFD simul ed the pattern is a predomi The sailing rate coast can few degrees o WSW conditi ° - 10 m/swind n blue color th or the positive fulness of d predictions se of CFD thro tware have the coastal w ite of Weymo e harbour and to observation l wind conditi e wind over Team in B nded by two s cean by a s lation of the w s of wind aro inant g in n be f the ions d he e CFD s for ough been wind outh, d hill ns of ions. the Brest, steep strait. wind. ound t o A t a f F c R 2 3 4 5 6 7 8 A M E e a t d e Y W F
26
TH– 28
the racing ar observations. Although no these two site agreement be flows and th Further inves compare meas REFERENC 1. GRYNIN BRUMM S., ‘On homogen Boundary 2. PEÑA A Universit 3. PEÑA A profile m European (EWEC), 4. BURCHA in marine 5. BAUMER moment stratified 105 (C3), 6. HAN J., ‘Estimati Energy D Boundary 2000-210 7. PETERSH turbulenc measurem 2007. 8. DUYNKE turbulenc atmosphe pp865-88 AUTHORS B M. Le Guell Engineer at F environment assessment st the wind field district for p energy assessm Y. Amice ho Weather, seco Federation.8
THJune, 20
rea which ar quantitative r es, the qualitat etween the n e sailing team stigations will surements of t ES NGS.-E., MERB., JØRG the extension neous terrain y-Layer Meteo ., ‘Sensing the ty of Copenha A., GRYNING much higher n Wind Energy Marseille, Fr ARDH., ‘App e Waters’, Spr RTH. Z. an closures and turbulent she , pp 6453-646 ARYA S.P., on of Turb Dissipation R y Layer Sim 0298, June 200 H. and BAU ce closure aga ments’, Ocean ERKE P.G., ce closure mo eric boundary 80, 1988. BIOGRAPHYlec holds the LUIDYN FR impact s tudies. His p d modelling at pedestrian com ment in hilly r olds the curr onded by the N
013
re compared results were y tive assessme numerically p m experience l be carried o the wind speeBATC GENSEN H., n of the win beyond the orol., 124, pp2 e wind profile agen, March 2 GS.-E., ‘Exten r than the gy Conference rance 16 - 19 M plied Turbule ringer, 2002. nd PETERS d length scal ear flows’, J. 68, 2000. SHEN S., and ulent Kinetic Rate Based o milarity Theor 00. UMERTH. Z. ainst estuarine n Modelling, , ‘Applicatio odel to the neu
layer’, J. Atm Y e current posi RANCE. He is studies and previous expe t local scale in mfort assessm region. rent position Navy with the
with empiric yet available o ent show a goo predicted win e on the wate out in order ed and directio CHVAROVAE and LARSE nd profile ov surface laye 251–268, 200 e’, Ph.D. Thes 009.
nding the win surface laye e and Exhibitio
March 2009. ence Modellin
H., ‘Secon les for weak Geophys. Re d LIN Y-L.: A c Energy an on Atmospher ry’, NASA/CR , ‘Validating e microstructu 19, pp183–20 on of the k utral and stab mos. Sci., 45(5 ition of Proje responsible f consequen erience includ n complex urb ment and win
ofChief Pet e French Sailin cal on od nd er. to on. E., EN ver er’, 7. sis, nd er’, on ng nd-kly es., An nd ric R-a ure 03, k-ε ble 5), ect for nce des an nd tty ng
