Warm discharges in cold fresh water: 2. Numerical simulation of laminar line plumes

International Journal of Heat and Mass Transfer

Kay

2017

Self Cite

Laminar plumes from a line source of warm water at the base of a shallow, homogeneous body of cold water (below the temperature of maximum density)were simulated by a computational model. The plume water undergoes buoyancy reversal as it mixes with the cold ambient. If this occurs before the plume has reached the ceiling of the domain, the plume flaps from side to side. Otherwise, it spreads along the ceiling and then sinks, with a vortex enclosed between the rising plume and the sinking flow. Some of the dense, mixed water from the sinking flow is re-entrained into the rising plume, while the rest flows outwards along the floor. However, with high source temperatures, a sufficient volume of warm water eventually builds up to also form a positively buoyant gravity current along the ceiling.

mentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Numerical simulations of a line plume impinging on a ceiling in cold fresh water

International Journal of Heat and Mass Transfer

Kay

2017

Self Cite

Propagation Speed of the Frontal Head Through Lock-Exchange Density Current in Cold Fresh Water: Simulations without the Effect of Back-reflected Waves

Osaisai

2022

ARJOM

The behaviour of warm water discharged at 4\(^{\circ}\)C through lock-exchange in cold fresh water was investigated numerically, fixing lock volume at the centre of the domain. This investigation as presented here is practical and can also enhance policy making towards the protection of the aquatic ecosystems. Though, the aim of this study is to better fathom and as well, gain more insight into such ows. Our results have shown a speedy movement of the lock volume at the centre of the domain with a leading head at two front on the oor which resulted in a hat shape within the first few time frame. Fluid movement in the second phase is independent of the back reflected waves. We were able to identify two regimes of ow with a stepwise decreasing velocity in the second phase. Our results have shown that velocity with which the current travels with in the second regime is higher within the first time frame as compared to those with the effect of back reflected waves. One major factor that is responsible for decrease in the velocity here is mixing. Previous results have also shown that the front velocities in the collapsing phase are independent of lock volume. But this seem not to be the same here because fluid movement in the first phase (regime) is not totally independent of the lock volume and its position here, where density difference is as a result of temperature. However, our scaling power laws here in the second phase show some variations with previous studies where we have effect of back reflected waves. But results in the collapsing phase here are in strong agreement with those in the first phase of our previous simulations with small lock volume. Generally, the spreading behaviour here is dependent on lock volume, barrier position, density difference and Reynolds number.

Laminar Plumes from a Line Source and Their Possible Flow Behaviours

Osaisai²,

Dienagha³

2023

ARJOM

Numerical investigation on laminar plumes that under goes buoyancy reversal had just been made, fixing both Re & Pr and varying Fr during the simulations. Water density was taken as a quadratic function of temperature. The result showed some side-to-side apping and bobbing motion after the core of the fountain were exposed together with head detachment behaviour. At the fountains core, profiles of vertical velocity component show that decrease in vertical velocity with height is not smoother even at higher Froude numbers as compared to the case in our previous study for (Re = 50). Empirically determined scalings laws for fountain height and time to attain maximum height were obtained. Initially rising plumes were symmetric and takes much longer time to attain a fully developed stage as Fr increases before sufficient dense fluid is produced to halt their rise. Generally, we can conclude that with the quadratic dependence relation assumption, Irrespective of the ow parameters used within the Reynolds number range 50 \(\le\) Re \(\le\) 100 and Prandtl number Pr = 7&11:4 the ow behaviour remains the same. Except for the behaviour in the profiles of vertical velocity that show some slight differences as compared to our earlier investigation, and the Froude number that represents the balance between inertia and buoyancy forces (responsible for the variation in the fountains heights).