We present an experimental investigation, supported by a theoretical model, of the motion of loc... more We present an experimental investigation, supported by a theoretical model, of the motion of lock-release, constant inflow, and time varying inflow gravity currents (GCs) into a linearly stratified ambient fluid at large Reynolds number. The aim is the experimental validation of a simple model able to predict the slumping phase front speed and the asymptotic self similar front speed for rectangular and circular cross-section channels. A first system is of Boussinesq type with the dense current (salt water dyed with aniline) released in a circular channel of 19 cm diameter and 400 cm long (605 cm in the inflow experiments), half filled of linearly stratified ambient fluid (salt water with varying salt concentration). A second system has the same characteristics but with a rectangular cross-section of 14 cm width, 11 cm ambient fluid depth and 504 cm length. The density stratification of the ambient fluid was obtained with a computer controlled set of pumps and of mixing tanks. For the experiments with inflow a multi-pipes drainage system was set at the opposite end with respect to the inflow section, computer controlled to avoid the selective withdrawal. The numerous experiments (28 for circular cross-section, lock release; 26 for circular and 14 for rectangular cross-section, constant inflow (fluid volume $\propto t^{\alpha}$, with $\alpha=1$); 6 for circular cross-section, linearly increasing inflow ($\alpha=2$)), with several combination of the stratification parameter ($0<S<1$) confirm the theory within $\approx 30\%$ ($\approx 40\%$ for a single series of experiments), which is a good result also considering the numerous approximations. The results on the front speed of the GCs are discussed in the presence of the internal waves, which have a celerity given by a theoretical and experimentally tested model for the rectangular but not for the circular cross-section. The theoretical analysis of internal waves in circular cross-sections has been extended and experimentally validated.
We study axisymmetric gravity currents consisting of a constant or time-dependent volume of a pow... more We study axisymmetric gravity currents consisting of a constant or time-dependent volume of a powerlaw viscous fluid propagating on a horizontal rigid plane below a fluid of lesser density. The intruding fluid is considered to have a pure Ostwald–DeWaele power-law constitutive equation. First, the conditions for buoyancy–viscous balance are examined, and the current rate of spreading is derived with a box-model. An existing self-similar solution to the nonlinear differential problem for the influx of a constant or time-variable volume of fluid is then described. Results from a number of experiments conducted in a 30 sector with shear thinning, Newtonian and shear thickening fluids, and with constant and increasing release rate, are presented and interpreted with the theoretical solution, obtaining globally a very satisfactory agreement. The rheological parameters of the fluid, derived with a best fit procedure, are compared to those measured independently with conventional rheometry. Confidence intervals are evaluated for both estimates of flow behavior and consistency indices. Results support the feasibility of controlled constant flux laboratory experiments with gravity currents in axisymmetric geometry to infer the rheology of power-law fluids, especially at very low shear rates and with shear thinning fluids.
We present an experimental investigation, supported by a theoretical model, of the motion of loc... more We present an experimental investigation, supported by a theoretical model, of the motion of lock-release, constant inflow, and time varying inflow gravity currents (GCs) into a linearly stratified ambient fluid at large Reynolds number. The aim is the experimental validation of a simple model able to predict the slumping phase front speed and the asymptotic self similar front speed for rectangular and circular cross-section channels. A first system is of Boussinesq type with the dense current (salt water dyed with aniline) released in a circular channel of 19 cm diameter and 400 cm long (605 cm in the inflow experiments), half filled of linearly stratified ambient fluid (salt water with varying salt concentration). A second system has the same characteristics but with a rectangular cross-section of 14 cm width, 11 cm ambient fluid depth and 504 cm length. The density stratification of the ambient fluid was obtained with a computer controlled set of pumps and of mixing tanks. For the experiments with inflow a multi-pipes drainage system was set at the opposite end with respect to the inflow section, computer controlled to avoid the selective withdrawal. The numerous experiments (28 for circular cross-section, lock release; 26 for circular and 14 for rectangular cross-section, constant inflow (fluid volume $\propto t^{\alpha}$, with $\alpha=1$); 6 for circular cross-section, linearly increasing inflow ($\alpha=2$)), with several combination of the stratification parameter ($0<S<1$) confirm the theory within $\approx 30\%$ ($\approx 40\%$ for a single series of experiments), which is a good result also considering the numerous approximations. The results on the front speed of the GCs are discussed in the presence of the internal waves, which have a celerity given by a theoretical and experimentally tested model for the rectangular but not for the circular cross-section. The theoretical analysis of internal waves in circular cross-sections has been extended and experimentally validated.
We study axisymmetric gravity currents consisting of a constant or time-dependent volume of a pow... more We study axisymmetric gravity currents consisting of a constant or time-dependent volume of a powerlaw viscous fluid propagating on a horizontal rigid plane below a fluid of lesser density. The intruding fluid is considered to have a pure Ostwald–DeWaele power-law constitutive equation. First, the conditions for buoyancy–viscous balance are examined, and the current rate of spreading is derived with a box-model. An existing self-similar solution to the nonlinear differential problem for the influx of a constant or time-variable volume of fluid is then described. Results from a number of experiments conducted in a 30 sector with shear thinning, Newtonian and shear thickening fluids, and with constant and increasing release rate, are presented and interpreted with the theoretical solution, obtaining globally a very satisfactory agreement. The rheological parameters of the fluid, derived with a best fit procedure, are compared to those measured independently with conventional rheometry. Confidence intervals are evaluated for both estimates of flow behavior and consistency indices. Results support the feasibility of controlled constant flux laboratory experiments with gravity currents in axisymmetric geometry to infer the rheology of power-law fluids, especially at very low shear rates and with shear thinning fluids.
Uploads
Papers by Marius Ungarish
viscous fluid propagating on a horizontal rigid plane below a fluid of lesser density. The intruding
fluid is considered to have a pure Ostwald–DeWaele power-law constitutive equation. First, the conditions
for buoyancy–viscous balance are examined, and the current rate of spreading is derived with a
box-model. An existing self-similar solution to the nonlinear differential problem for the influx of a constant
or time-variable volume of fluid is then described. Results from a number of experiments conducted
in a 30 sector with shear thinning, Newtonian and shear thickening fluids, and with constant and
increasing release rate, are presented and interpreted with the theoretical solution, obtaining globally
a very satisfactory agreement. The rheological parameters of the fluid, derived with a best fit procedure,
are compared to those measured independently with conventional rheometry. Confidence intervals are
evaluated for both estimates of flow behavior and consistency indices. Results support the feasibility
of controlled constant flux laboratory experiments with gravity currents in axisymmetric geometry to
infer the rheology of power-law fluids, especially at very low shear rates and with shear thinning fluids.
viscous fluid propagating on a horizontal rigid plane below a fluid of lesser density. The intruding
fluid is considered to have a pure Ostwald–DeWaele power-law constitutive equation. First, the conditions
for buoyancy–viscous balance are examined, and the current rate of spreading is derived with a
box-model. An existing self-similar solution to the nonlinear differential problem for the influx of a constant
or time-variable volume of fluid is then described. Results from a number of experiments conducted
in a 30 sector with shear thinning, Newtonian and shear thickening fluids, and with constant and
increasing release rate, are presented and interpreted with the theoretical solution, obtaining globally
a very satisfactory agreement. The rheological parameters of the fluid, derived with a best fit procedure,
are compared to those measured independently with conventional rheometry. Confidence intervals are
evaluated for both estimates of flow behavior and consistency indices. Results support the feasibility
of controlled constant flux laboratory experiments with gravity currents in axisymmetric geometry to
infer the rheology of power-law fluids, especially at very low shear rates and with shear thinning fluids.