FLOW AROUND A CYLINDER - istiarto

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– 3.6 – Fig. 3.1 Cont’d. � In the plane � = 135°, leaving the cylinder. The u component diminishes over the entire depth, but has always positive values. The v component remains negligible in the upper layer, but decreases in the lower layer where it becomes negative for r > 22 [cm]. The w component exhibits a rather weaker downward flow than in the previous planes, being w U � � �0.3. This component looses its strength and becomes negligible for r > 70 [cm]. � In the plane � = 180°, leaving the cylinder. The u component shows a flow reversal towards the surface, its profile shows a recovery towards the one of uniform flow. The v component is generally small, but is rather noticeable, v U � � �0.1, close to the cylinder. The w component is, contrary to that in the other planes, always directed upward and diminishing.
3.2.2 Flow pattern around the cylinder – 3.7 – A further investigation on the flow field can be made by presenting the measured velocity data in vector plots as depicted in Fig. 3.2. The plots, however, offer only a 2D picture of the flow field. In order to obtain a better observation on the flow structure around the cylinder, isoline contours of the velocity magnitude in different planes are plotted in Fig. 3.3. The velocity magnitude is normalized by the velocity of the approach flow, V U � , where V � u 2 � v 2 � w 2 and U � � 0.45 [m s]. This can be interpreted as the flow intensity. These two figures together give a clear idea about the flow pattern around the cylinder. In the following paragraphs, the flow pattern around the cylinder is discussed, firstly for the plane of symmetry upstream of the cylinder (� = 0°) and secondly for the other planes (� = 45°, 90°, 135°, and 180°). Flow in the plane � = 0°� � The (far-field) approach flow, being essentially uni-directional, undergoes a separation upon encountering the sloping bed of the scour hole (see Fig. 3.2a). This process is similar to that of flow over a back-facing step (see Nakagawa and Nezu, 1987), except that the separation does not take place immediately at the tip of the bed change but at a point further downstream. By visual observation, the separation starts approximately at 5 [cm] after the sloping bed starts. Underneath the separation line, a weak clockwise rotating flow forms itself. � Above the separation line, the flow is decelerating notably in the region r > 30 [cm]. Within a short distance 20 ≥ r [cm] ≥ 14, the flow intensity decreases from V U � � 0.8 to 0.6 (see Fig. 3.3a). This decelerating flow is associated with a reverse pressure gradient created by the cylinder, which develops into a stagnation pressure at the cylinder face. In the vertical direction, the (dynamic) pressure diminishes with increasing depth (decreasing z). Consequently, the flow is down-deflected that becomes more pronounced approaching the cylinder. A strong downward flow develops along the cylinder face. � The downward flow gets stronger with increasing depth, reaches a peak value of �w U � � 0.6 (Fig. 3.1) somewhere below the original bed level (Sect. 3.2.4 will discuss further the distribution of the maximum downward velocity). Below the peak, the (downward) flow looses its intensity from V U � � 0.6 to 0.2 (see Fig. 3.3a) when it encounters the separation zone and interacts with the rotating flow already exists there. The downward flow enhances the rotating flow and, conversely, the rotating flow attenuates the downward flow. At the bed, the flow is reversed back towards upstream by the cylinder and the bed; this further strengthening the rotating flow. This system of rotating and downward flows, which continues to exist as one follows the angular direction around the cylinder, is better known as the horseshoe vortex.
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FLOW AROUND A CYLINDER IN A SCOURED
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- iii - Flow around a Cylinder in a
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- v - Écoulement à Surface Libre
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- vii - Acknowledgements I wish to
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- ix - Table of Contents Abstract i
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- xi - 4.4 Pressure-velocity coupli
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Chapter 1 - 1.i - 1 Introduction 1.
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1 Introduction 1.1 Flow around a cy
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- 1.3 - pitot tubes. Ahmed and Raja
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Chapter 2 - 2.i - 2 Flow Measuremen
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2 Flow Measurements Abstract - 2.1
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2.1 Measurement design - 2.3 - The
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- 2.5 - The water circuit is a clos
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- 2.7 - Consider a target ―i‖ m
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- 2.9 - Obtaining the velocity comp
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- 2.11 - Fig. 2.4 Cartesian and cyl
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- 2.13 - transducer were used, a fo
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- 2.15 - typically needed for this
Page 37 and 38: - 2.17 - 2.3.3 Comparison to other
Page 39 and 40: - 2.19 - Fig. 2.7 Scour hole geomet
Page 41 and 42: - 2.21 - Fig. 2.8 Distributions of
Page 43 and 44: u ��u �� u� � Du exp�
Page 45 and 46: - 2.25 - �o , and accordingly the
Page 47 and 48: - 2.27 - Measurements in zone A. Th
Page 49 and 50: - 2.29 - and 0.3 u �� u ��
Page 51 and 52: - 2.31 - Fig. 2.12b Cont’d.
Page 53 and 54: - 2.33 - Fig. 2.12d Cont’d.
Page 55 and 56: 2.5.4 Measurements in the plane �
Page 61 and 62: - 2.41 - the solid boundary of the
Page 67 and 68: - 2.47 - Turbulence intensities in
Page 69 and 70: - 2.49 - Fig. 2.15a Vertical distri
Page 71 and 72: - 2.51 - Fig. 2.15c Cont’d.
Page 73 and 74: - 2.53 - Reynolds stresses in the p
Page 75 and 76: - 2.55 - Fig. 2.16c Cont’d.
Page 77 and 78: 2.6 Summary and conclusions - 2.57
Page 79 and 80: - 2.59 - Rolland, T. (1994). Develo
Page 81 and 82: Chapter 3 - 3.i - 3 Elaboration of
Page 83 and 84: - 3.1 - 3 Elaboration of the measur
Page 85 and 86: 3.1 Introduction - 3.3 - Presented
Page 87: - 3.5 - Fig. 3.1 Measured velocity
Page 91 and 92: - 3.9 - Fig. 3.2 Cont’d.
Page 93 and 94: Flow in the plane � = 45° and 90
Page 95 and 96: - 3.13 - Fig. 3.4 Contours of the m
Page 97 and 98: 3.2.4 Vertical velocity (downward f
Page 99 and 100: - 3.17 - flow may undergo a rotatin
Page 103 and 104: - 3.21 - A similar observation, in
Page 105 and 106: - 3.23 - Fig. 3.9 Measured turbulen
Page 107 and 108: The following is to be observed: -
Page 111 and 112: - 3.29 - 3.4 Bed shear-stresses alo
Page 113 and 114: x [cm] - 3.31 - Table 3.1 Estimated
Page 115 and 116: - 3.33 - Fig. 3.12 Estimated bed sh
Page 117 and 118: - 3.35 - (see Fig. 3.10 and Fig. 3.
Page 119 and 120: - 3.37 - Fig. 3.14 Axonometric pres
Page 121 and 122: - 3.39 - U, U∞ [m/s] sectional av
Page 123 and 124: Chapter 4 - 4.i - 4 Numerical Model
Page 125 and 126: - 4.1 - 4 Numerical Model Developme
Page 127 and 128: �u �t �v �t �w �t �
Page 129 and 130: - 4.5 - The volume integrals of the
Page 131 and 132: - 4.7 - Fig. 4.1 Overall iterative
Page 133 and 134: - 4.9 - increase the computer stora
Page 135 and 136: - 4.11 - �� 1 ��
Page 137 and 138: - 4.13 - convective transport throu
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- 4.15 - n,��1 during a time st
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� for 0 � Pe e � q eL PE �
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4.3.8 Source terms - 4.19 - The sou
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2D � � � x �� b 2D �
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- 4.23 - b T � V P �t � n P
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- 4.25 - �� u ��1 � c i
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- 4.27 - Next, we need to define th
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4.5 Boundary conditions 4.5.1 Bound
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- 4.31 - The above relation holds a
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- 4.33 - � extrapolate all variab
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G � � t 2 �V t - 4.35 - 2 �
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with � �� nt,b � ��
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- 4.39 - boundary node B are then a
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- 4.41 - Wall function for the �
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k and � equations - 4.43 - � se
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�� z-momentum: - 4.45 - ��1
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- 4.47 - � reconstruct the mesh,
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- 4.49 - Fig. 4.13 The structure of
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- 4.51 - ��
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4.7 Summary - 4.53 - Development of
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- 4.55 - B, �B [-] constant and w
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- 4.57 - �, � 1 , � p [-] und
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Chapter 5 - 5.i - 5 Numerical Simul
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5 Numerical Simulation Abstract - 5
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5.2 Experimental data - 5.3 - 5.2.1
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- 5.5 - computational nodes. The ot
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- 5.7 - (i) Yulistiyanto data (ii)
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- 5.9 - ( p � � 1 [mm]), but th
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- 5.11 - Fig. 5.4 Model test result
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- 5.13 - within a greater number of
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- 5.15 - Fig. 5.6 Computational his
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- 5.17 - 5.5 Simulation of flow aro
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- 5.19 - Fig. 5.9 Definition sketch
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- 5.21 - Fig. 5.10 Computed (lines)
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- 5.23 - Fig. 5.11 Computed and mea
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- 5.25 - 1.2U ∞ of the measuremen
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Water-surface profile - 5.27 - The
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- 5.29 - using a Joukowski transfor
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- 5.31 - 5.6.3 Results of the simul
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Velocity fields around the cylinder
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- 5.35 - Fig. 5.18 Computed and mea
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- 5.37 - than the measured one. The
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- 5.39 - Production and dissipation
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- 5.41 - Production of turbulent ki
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- 5.43 - If the above approach were
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- 5.45 - and surface profiles (see
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- 5.47 - Fig. 5.24 Surface boundary
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- 5.49 - S [m 2 ] surface area. So,
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Chapter 6 - 6.i - 6 Summary and Con
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- 6.1 - 6 Summary and Conclusions 6
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- 6.3 - The spatial distributions o
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- 6.5 - � Laboratory measurements
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- 6.7 - Fig. 6.1 Measured and compu
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IDENTITE - 7.1 - Curriculum Vitæ N
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- iii - Appendices Appendix A: Expe
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A Experimental Data - A.1 - The exp
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B Numerical Model B.1 Program struc
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- B.3 -
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B.2 Input data file - B.5 - The inp
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- B.7 - #31 imon1, jmon1, kmon1 thr
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BLO for blocked cells, INL for inle
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