A 2D Finite Volume Non-hydrostatic Atmospheric Model ...

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$Departments of Mathematics and Physics (D-MATH/D ... - RW/CSE$

1.2 MotivationIn [6] Wunderlich implemented a 2D well balanced finite volume method based on the ideas of Botta etal. in [5]. He used a terrain-following vertical coordinate in his model. In this work we adapt the modelto a cut-cell approach and compare it to the terrain-following approach. To improve performance the hydrostaticbackground state is no longer calculated in every time step. It is rather kept constant for a numberof time steps. Nevertheless the deviation of the complete state from the hydrostatic background stateremains small as long as the background state is reconstructed reasonably often. Since the original modelis very sensitive to the choice of the divergence damping coefficients, the divergence damping term isreviewed. Then, the following improvements are made to the model:The implemented divergence damping is corrected (see section 4.2)Computational mixing is added in order to remove small scale noise of computational origin(section 4.3)Physical mixing is added to simulate diffusion (section 4.4)A Rayleigh sponge layer at the top of the domain is introduced in order to absorb upward propa-gating waves (section 4.5)To test the improved model several tests are undertaken. The test cases includeLinear, non-hydrostatic flow (see section 6.3)Linear, hydrostatic flow (section 6.4)Flow over a Schär hill (section 6.5)Development of a negative buoyant thermal bubble (section 6.6)Atmosphere at rest over steep topography (section 6.7)2
$$%&$$00++$$$$$$2 Governing equations and the discrete Archimedes' principle2.1 The inhomogeneous Euler equationsThe inhomogeneous Euler equations constitute a hyperbolic system of conservation laws where the conservedquantities are the mass, the momenta in every space dimension and the total energy. In two spacedimensions x and z the inhomogeneous Euler equations are given bytu w e & ('*) u u 2 & p x uw + u & ,' & e p .- &wuww 2 pw e p00z g 34 02.1 where is the density, u and w are the horizontal and vertical velocities, p is the pressure, e is the sumof the internal and the kinetic energy, gz is the time independent gravitation potential with g thegravitational acceleration and z the elevation above sea level. The pressure p is related to the flux variables , u , w and e over the thermodynamic equation of statep 5 687.9 , 9 u , 9 w , 9 e: :527.;=< 1:>7.9 e
Page 1: A 2D Finite Volume Non-hydrostatic
Page 5: List of figuresFigure 5.1: Illustra
Page 8 and 9: £¤¢¦§©¡¨¥NomenclatureQDamp
Page 15: Cc iR iO'0PPc iPc i/OCc iR ih OO'''
Page 18 and 19: €€€uuG tQ ijt s 0tuww€wwt s
Page 20 and 21: ¼¼µ½¼u¼½u}}}3.5 Reconstructi
Page 22 and 23: ÍãååÌÌ ÍãÍãååçããÍn
Page 24 and 25: ðåùÏÕìãããìëxÏìÞÏãÖ
Page 27 and 28: 6
Page 29 and 30: q ijCRJ Zq i , jP 1 Sq p " RJ""q r
Page 31: 5.3 Terrain-following gridThe terra
Page 34 and 35: 6.2 Performance improvementThe main
Page 36 and 37: 6.3 Linear, non-hydrostatic flowWit
Page 38 and 39: 6.3.2 Impact of the corrected diver
Page 40 and 41: 6.3.4 The effects of computational
Page 42 and 43: elative horizontal velocity u [m/s]
Page 44 and 45: vertical velocity w [m/s]8000700060
Page 46 and 47: Figure 6.11: Simulation of a negati
Page 48 and 49: Figure 6.12: Time evolution of maxi
Page 51: References[1] Klemp, J.B., Skamaroc

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