Changes between Version 74 and Version 75 of WikiStart


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Timestamp:
Sep 20, 2016, 5:18:35 PM (4 years ago)
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peakall3je
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    7373[[BR]]
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    7574
    7675= 6 - Table of Experiments: =
     
    9190
    9291= 7 - Diary: =
     92
     93= Monday September 19th 2016 =
     94
     95Experiment name: fixstr1_1909A
     96Filenames: fixstr1_1909A1, fixstr1_1909A2
     97Location: Position 1 (75% of the way down the straight section, 58 cm upstream from the end of straight section). Input rate: 12 l/s, density excess: 20 kg/$m^3$. Water was very cloudy to the extent that we were not able to use the laser. No siphon rig was used. Running basal ADV with ADV #1 located 7.2 cm from the base. ADV just measured at one point (no traverse measurement).
     98
     99Experiment started at 2:45pm and stopped at 3:15 pm. The flow automatically stopped part way through as a valve was not open for recirculating water. Part way through red dye was added to visualise the current. Dye visualisation suggested pretty thin flow on the inner bank and significant super elevation on the outer bank. Some perturbation was observed on the surface of the flow at the outer bank, but otherwise the flow surface appears quite smooth, and mixing appeared to be very low. Mean maximum flow velocity from raw output was around 20 - 25 cm/s. ADV and UVP measured twice, the first is referred to as fixstr1_1909A1 and this had a velocity range of 0.3 m/s on the ADV setting, and 0.25 m/s for the UVP. Instantaneous flow velocities were faster than anticipated, as a result of the steep slope (3.5 degrees) with flow wrapping on both instruments so the velocity range was increased on the ADV and the UVP. A second run period fixstr1_1909A2 had a velocity range of 0.5 m/s on the ADV setting. The UVP setting was 680 mm/s (0.68 m/s).
     100
     101
     102= Tuesday September 20th 2016 =
     103Paint was applied to the tank floor to address a leak in the flume, and the tank floor left to dry and seal. The siphon rig was completed and tested. The laser system was aligned. The position of the basal ADV was refined, Orgasol was required as additional seeding in order for bottom tracking to work effectively. Interesting, the stem (fixed) ADV picks this bottom point up better than the flexible ADV in the absence of seeding. Tested synchronization of ADV with traverse; a problem was identified with the nature of the required input signal. Investigation in progress as to how to address this.
     104
     105
     106
     107
     108[[PageOutline]]
     109
     110= '''Project Name''' =
     111||Infrastructure||CNRS_Coriolis||
     112||Project (long title)||Coriolis and Rotational effects on Stratified Turbulence||
     113||Campaign Title (name data folder)||16CREST||
     114||Lead Author||Jeffrey Peakall||
     115||Contributor||Stephen Darby, Robert Michael Dorrell, Shahrzad Davarpanah Jazi, Gareth Mark Keevil, Jeffrey Peakall, Anna Wåhlin, Mathew Graeme Wells,   Joel Sommeria, Samuel Viboud||
     116||Date Campaign Start||12/09/2016||
     117||Date Campaign End||21/10/2016||
     118
     119[[BR]]
     120
     121= 1 - Objectives =
     122
     123Our primary objective is to measure detailed turbulence distributions within channelised gravity currents, as a function of Coriolis forces, concentrating on: i) the bottom boundary layer, ii) redistribution of turbulence within bends, and, iii) redistribution of turbulence at the interface between the gravity current and the ambient. These datasets will enable existing theory on the presence and influence of Ekman boundary layers to be tested, with important implication for the basal shear stress distributions, erosion, and the evolution of channels. These data on the distribution of turbulence will then be applied to i) examine the turbulence distribution in straight channels, ii) provide an analysis of secondary flow and associated turbulence around bends for the first time, and an assessment of how channelized flows alter as a function of Rossby numbers and therefore latitude, iii) assess how the morphodynamics of submarine channels vary as a function of the Rossby number, iv) explain the observed patterns of submarine channel sinuosity with latitude (Peakall et al., 2012; Cossu and Wells, 2013; Cossu et al., 2015), and, v) incorporate the entrainment data into numerical models of submarine channels, in order to address the unanswered question of how these flows traverse such large-distances across very low-angle slopes (Dorrell et al., 2014).Our primary objective is to measure detailed turbulence distributions within channelised gravity currents, as a function of Coriolis forces, concentrating on: i) the bottom boundary layer, ii) redistribution of turbulence within bends, and, iii) redistribution of turbulence at the interface between the gravity current and the ambient. These datasets will enable existing theory on the presence and influence of Ekman boundary layers to be tested, with important implication for the basal shear stress distributions, erosion, and the evolution of channels. These data on the distribution of turbulence will then be applied to i) examine the turbulence distribution in straight channels, ii) provide an analysis of secondary flow and associated turbulence around bends for the first time, and an assessment of how channelized flows alter as a function of Rossby numbers and therefore latitude, iii) assess how the morphodynamics of submarine channels vary as a function of the Rossby number, iv) explain the observed patterns of submarine channel sinuosity with latitude (Peakall et al., 2012; Cossu and Wells, 2013; Cossu et al., 2015), and, v) incorporate the entrainment data into numerical models of submarine channels, in order to address the unanswered question of how these flows traverse such large-distances across very low-angle slopes (Dorrell et al., 2014).
     124
     125[[BR]]
     126
     127= 2 - Experimental setup: =
     128
     129[[Image(Set_up_drawing.jpg)]]
     130 
     131
     132
     133== 2.1 General description ==
     134
     1352.1 General description
     136A channel model is positioned within the Coriolis facility. The channel model consists of an initial tapered input section with a honeycomb baffle for flow straightening and turbulence control, a 3.2 m straight channel section, and two bends with a mid-channel radius of 1.5 m. The channel is made of acrylic and is 60 cm wide and 50 cm high; the sinuous section has a sinuosity of 1.2. The slope is 3/50 radians (3.5 degrees, 6% gradient) and the channel terminates 10 cm off of the floor. Saline fluid is pumped into the top of the channel, forming a gravity current, which flows along the channel, and off the end. The basal 10 cm of the flume operates as a sump for the denser saline fluid to accumulate. In turn, this fluid can be drawn down in one of two ways: i) whilst recirculating the fluid, though this is limited to 20 $m^3$/hr (5.55 l/s), and ii) through emptying to the drain, in which case any flow rate is possible.
     137Two long metal rails are positioned to either side of the channel model across the full width of the flume. These carry a computerized gantry, which can be positioned at any point along the channel. The gantry itself contains the controls for two Schneider slides, one orientated transverse to the model, and the other connected slide, orientated in the vertical. Thus the system enables xyz control.
     138
     139
     140== 2.2 Definition of the co-ordinate system ==
     141
     142
     143== 2.3 Fixed Parameters ==
     144
     145||'''Notation'''||'''Definition'''||'''Values'''||'''Remarks'''||
     146|| $Q_0$ || Input Density || $12 \ ls^-^1$ || ||
     147|| $\Delta\rho$ || Density Difference || $20 \ kg \ m^-^3$  || ||
     148|| $W$ || Channel Width || $0.6 \ m$ || ||
     149|| $\nu$ || Viscosity || $10^-^6m^2s^-^1$ || ||
     150|| $S$ || Slope|| $3.5^{\circ}$ || ||
     151
     152
     153== 2.4 Variable Parameters ==
     154
     155||'''Notation'''||'''Definition'''||'''Unit'''||'''Initial Estimated Values'''||'''Remarks'''||
     156|| $\Omega$ || Rotation Rate || $rads^-^1$ || -0.18 - 0.15 || ||
     157|| $H_w$ || Water Depth || $m$ || 1-1.1 || ||
     158|| $Q_o_u_t_p_u_t$ || Output Flow Rate || $ls^-^1$ || 5.5 - 17 || ||
     159|| $k$ || Roughness || - || -  || ||
     160
     161== 2.5 Additional Parameters ==
     162
     163||'''Notation'''||'''Definition'''||'''Unit'''||'''Initial Estimated Values'''||
     164|| $h$ || Depth of gravity current || $m$ || 0.1 ||
     165|| $U$ || Mean downslope velocity || $m^s^-^1$ || 0.1-0.15 ||
     166|| $\delta$ || Thickness of Ekman boundary layer || $mm$ || ~10 ||
     167|| $R$ || Radius of curvature || $m$ || 1.5 ||
     168
     169== 2.6 Definition of the relevant non-dimensional numbers ==
     170
     171Flow Reynolds number across the obstruction, $Re = Uh/\nu$.
     172
     173Densimetric Froude number, $Fr = U/(g'h)^{1/2}$, $g' = g(\Delta\rho)/\rho_0$.
     174
     175Rossby number, $Ro = U/fW$.
     176
     177Canyon number, $\beta = sW/\delta$.
     178
     179[[BR]]
     180
     181
     182= 6 - Table of Experiments: =
     183
     184||'''Run Name'''||'''Downstream (x)Position'''||'''Density Excess '''||'''Input flow'''||'''Rotation Rate'''||'''Initial Water Depth'''||'''Outflow Rate'''||'''Run Time'''||'''ADV Dwell Time'''||
     185|| ||  || $(kg \ m^-^3)$ || $(ls^-^1)$ || $(rad \ s^-^1)$ || $(m)$ || $(ls^-^1)$ || $(Minutes)$ || $(s)$ ||
     186||fixstr1_1909A|| xx || 20 || 12 || 0 || 1 || 5.5 || 30 || continuous ||
     187||fixstr1_2009A|| xx || 20 || 12 || 0 || 1 || 5.5 || 20 || 60 ||
     188||Smooth_3|| 2 || 20 || 12 || 0 || 1 || 5.5 || 20 || 60 ||
     189||Smooth_4|| 3 || 20 || 12 || 0 || 1 || 5.5 || 20 || 60 ||
     190||Smooth_5|| 4 || 20 || 12 || 0 || 1 || 5.5 || 20 || 60 ||
     191||Smooth_6|| 1 || 20 || 12 || 0 || 1 || 5.5 || 20 || 30 ||
     192||Smooth_7|| 3 || 20 || 12 || 0 || 1 || 5.5 || 20 || 30 ||
     193||Smooth_8|| 4 || 20 || 12 || 0 || 1 || 5.5 || 20 || 30 ||
     194||Smooth_9|| 2 || 20 || 12 || 0 || 1 || 12.0 || 60 || 30 ||
     195
     196[[BR]]
     197
     198= 7 - Diary: =
    93199= fixstr1_1909A - 19/09/2016 =
    94200