The Forcing of Wind Turbine Rotors by True Weather Events as a Function of Atmospheric Stability State*

Transcription

1 NAWEA 2015 Symposium 11 June 2015 Virginia Tech, Blacksburg, VA The Forcing of Wind Turbine Rotors by True Weather Events as a Function of Atmospheric Stability State* Balaji Jayaraman 1 and James G. Brasseur 1 Collaborators: Jared Lee 2, Tyler McCandless 2 and Sue Haupt 2 1 Department of Mechanical Engineering, The Pennsylvania State University, USA 2 National Center for Atmospheric Research (NCAR), USA *Supported by: DOE (EERE) Offshore Wind Technology Development Program Computer Resources: NSF XSEDE program; Penn State University Institute of Cyber Science 1

2 The DOE Penn State Cyber Wind Facility Program Weather Research and Forecasting (WRF) MESOSCALE, WEATHER (URANS/WRF) *ATMOSPHERIC BOUNDARY LAYER TURBULENT WINDS (4-D LES) ABL-LES *PLATFORM-WAVE HYDRODYNAMICS and 6-DOF MOTIONS (Hybrid URANS/LES +VOF) *BLADE AERODYNAMICS, SPACE-TIME LOADINGS (Hybrid URANS/LES) *Shaft Torque, *Drivetrain Loadings WAKE TURBULENCE BLADE-WAKE-ATMOSPHERE (Actuator Vortex Body Embedding within LES) WAKE- TURBINE INTERACTIONS (wind plant) *BLADE AND *TOWER ELASTIC DEFORMATION (FEM, Modal model + FSI) *sensors, controllers, diagnostics CYBER WIND FACILITY highly resolved 4-D cyber data coupled atmospheric turbulence-blade loadings-shaft torque data

3 Daytime Atmospheric Boundary Layer (ABL) and Stability θ=potential temperature z i Θ SHEAR -<uw> U M - (mesoscale wind) BUOYANCY (CONVECTION) <wθ> Solar heating Q 0 (>0) buoyancy-dominated MIXED LAYER Shear-dominated SURFACE LA YER Q 0 >0 z i - Inversion Height of the ABL 3 u* L Q g / T 0 0 Obukhov Length ABL Stability parameter: -z i /L -z i /L << 1 near neutral ABL (purely shear-driven) -z i /L ~1-10 Moderately convective (shear & buoyancy) -z i /L >>1 Convective (purely buoyancy-driven) 3

4 Canonical Equilibrium ABL Turbulence Equilibrium ABL is well understood Large Eddy Simulation (LES) Field Experiments NEUTRAL (NBL) Streaks MODERATELY CONVECTIVE (MCBL) Rolls Businger (1971) Solar heating Q 0 (>0) Khanna & Brasseur, 1998; Moeng & Sullivan,1994, Jayaraman & Brasseur (in preparation) Canonical Equilibrium ABL: (a) Horizontal homogeneity (roughness, Q 0,U M. ) (b) Quasi-stationarity How non-stationarity in Q 0 and U M impact ABL structure? 4

5 Mesoscale-driven Non-Stationary ABL WRF: Weather Research and Forecasting Wind magnitude U g (t) 700 km Mid-Western USA (WRF domain) (Apr, 15 th, 2012) Q 0 U M (t) 1 WRF cell (5km) = size of LES domain for ABL Wind direction U M (t)-direction Define 1100 km U g (t)-direction Dynamical relationship between and is : Non-stationary ABL In the stationary limit, Stationary/ Equilibrium ABL Non-stationarity in U M Deviation of U g from U M Non-equilibrium ABL? 5

6 LES of Non-stationary ABL Pseudo-spectral algorithm Mesoscale Wind, U M (t) Grid: 324x324x144 before dealiasing. SFS model: 1-eq. eddy viscosity. Periodic 2 km Non-stationarity: U M (t) and Q 0 (t) from WRF data. Surface Flux BCs Q 0 (t) 5 km Series of academic Dissection cases for fundamental analysis Dynamical Relationship between U M (t) and U g (t) : Continuity: Momentum: Potential Temperature: Bousinesq Coriolis 6

7 Non-equilibrium Effects: From Nonstationarity in Surface Heat Flux (Diurnal Changes) Q 0 U M (t) (symmetric) U g (t) U M (t)-direction U g (t)-direction MCBL NBL -z i /L Time Q 0 (K.m/s) -z i /L U M (t) (m/s) Non-stationarity (diurnal) in Q 0 Deviation from equilibrium of ABL Turbulence. 7

8 Non-equilibrium Effects: Q 0 time history on ABL Stability 8 Asymmetric 1 Asymmetric 2 Q 0 Q 0 Moderately convective ABL -z i /L -z i /L Neutral ABL Structure of ABL turbulence depends not-only on non-stationarity, but also on timehistory deviation from equilibrium

9 9 Change in ABL Stability from Changing Wind Direction Case 1 (f and ω ) blue- U M (t)-direction Case 2 (f and ω ) red - U g (t)-direction case 1 U M ω Case 1 f (out of plane) case 2 ω U M Case 2 Q 0 is invariant and non-zero. U M is constant with time ABL unstable ABL neutral Change in direction of U M alone modifies z i /L.

10 Why does ABL stability state change with no change in Q 0? Case 1 (f and ω ) Case 2 (f and ω ) u * u * - z i L = z kq g / T i 0 0 = k w 3 * 3 3 u * u * 1/u* 3 1/u* 3 κw* 3 κw* 3

11 Change in Wind Direction can alter ABL Structure 11 Q 0 is invariant and non-zero. blue- U M (t)-direction red - U g (t)-direction Initial z i /L = 0.41 U M is constant with time unstable 6 near neutral 5 Relationship between stability state, z i /L and ABL turbulence structure (next slide)

12 Effect of Change in Wind Direction : ABL Turbulence 3D Structure 1: -z i /L = : -z i /L = : -z i /L = AM PM 14.:11 PM 4 : -z i /L = : -z i /L = : -z i /L = :28 PM 16:56 PM 17:30 PM u -isocontours (-2σ u to +2σ u ) at 10% ABL height 12

13 Forcing of Wind Turbine Rotors by ABL Turbulence 13 Rotor in daytime ABL Turbulence Blade cuts through eddies Non-steady changes in sectional flow angles 3D non-steady separation dynamics and transient loadings Image made by Adam Lavely at Penn State CWF Passive Wind Turbine Analysis Imagine a hypothetical wind turbine in ABL flow Effect of wind turbine on ABL flow is not modeled Estimate temporal variations in Flow Angles relative to blade sections

14 Forcing of WT Rotors by Equilibrium ABL Turbulence Single blade section at R=60m, Hub height = 90 m RPM = 12 Pitch = twist = 0 o 10 min window 7-hours U hub Near-Neutral ABL -z i /L=0.41 <θ> 4 o Δθ 3 o θ θ U hub Moderately Convective BL -z i /L=2.4 θ Δθ 8 o <θ> 11 o

15 Forcing of WT Rotors by ABL Turbulence : Non-equilibrium ABL Q 0, U M are invariant U M (t)-direction U g (t)-direction Single blade section at R=60m, Hub height = 90 m RPM = 12 Pitch = twist = 0 o θ Unstable ABL θ Δθ 3.5 o 8-hours Δθ 2.5 o Neutral ABL

16 Summary Performed LES studies of non-stationary mesoscale forcing of ABL Non-stationarity in mesoscale occurs from two sources (a) U M (t) and Q o (t) diurnal cycle (b) Non-stationarity causes the mesoscale wind vector, U M (t) to deviate from the geostrophic wind vector, U g (t). Non-stationarity Non-equilibrium ABL turbulence With a non-zero steady surface heat flux, Q o, change in direction of mesoscale wind vector, U M (t) can modify ABL stability state. Time history of diurnal variation of Q 0 causes deviation of the ABL from equilibrium. Preliminary experiments indicate change in z i /L changes the mean and small-scale variability of the flow angles differently in equilibrium and non-equilibrium forcing. 16