Ruo-Qian Wang

Buoyant formation number of a starting buoyant jet

Understanding the influence of buoyancy on the formation number is important for analyzing the development of a starting buoyant jet and the interactions between its vortex ring and trailing stem. Numerical simulations with a large-eddy simulation model are performed to reproduce the starting buoyant jet in conditions ranging from pure jet to lazy plume. From the results, an improved method to determine the formation number is proposed based on the occurrence of a step jump in the vortex ring circulation. A comparison of the numerical results with the experimental data for a starting pure jet is first performed. The widely accepted formation number (≈4.0) is obtained, which implies that the method is satisfactory. The effect of buoyancy on the formation number is then investigated for two turbulent discharge conditions of Re=2000 and 2500 and with a wide range of buoyancy flux. Best-fit results are obtained that correlate the formation number with the Richardson number. Finally, a slug model that incorpor...

Pinch-off and formation number of negatively buoyant jets

Previous investigations of starting buoyant jets are extended towards negative buoyancy to address key issues in the formation processes. A series of large-eddy simulations (LES) is performed to identify whether an optimal vortex can be formed with negative buoyancy and if so what the corresponding formation number would be. The numerical code was previously validated for non-buoyant and positively buoyant jets and is further validated here for negatively buoyant jets using literature data on submerged fountains. Subsequently, jets with a range of negative buoyancies are simulated using source Reynolds numbers of 2000   0 for positively buoyant jets, Rid = 0 for non-buoyant jets, and Rid < 0 for negatively buoyant jets. Simulations identify two ranges of negative buoyancy. For weakly negatively buoyant starting jets (– 0.05 <∼ Rid < 0), the pinch-off and formation of an opt...

Scaling Particle Cloud Dynamics: From Lab to Field

AbstractOpen-water disposal of sediment is an important component in many coastal engineering projects. Numerous studies have focused on small-scale dynamics and claimed their results can be scaled up by cloud number scaling. However, this scaling method is largely empirical and unexamined. The present paper confirms that the cloud number scaling provides a rational way to extrapolate small-scale lab experiments or numerical simulations to the field operations.

A Mathematical Model for Pressure Compensating Emitters

This paper presents a mathematical model investigating the physics behind pressure-compensating (PC) drip irrigation emitters. A network of PC emitters, commonly known as drip irrigation, is an efficient way to deliver water to crops while increasing yield. Irrigation can provide a means for farmer to grow more sensitive, and profitable crops and help billions of small-holder farmers lift themselves out of poverty. Making drip irrigation accessible and economically viable is important for developing farmers as most face the challenges of water scarcity, declining water tables and lack of access to an electrical grid. One of the main reasons for the low adoption rate of drip irrigation in the developing world is the relatively high cost of the pumping power. It is possible to reduce this cost by reducing the required activation pressure of the emitters, while maintaining the PC behavior. The work presented here provides a guide of how design changes in the emitter could allow for a reduction in the activation pressure from 1 bar to approximately 0.1 bar. This decrease in the activation pressure of each emitter in turn decreases the system driving pressure. This reduction of driving pressure will decrease the energy need of pumping, making a solar-powered system affordable for small-acreage farmers.This paper develops a mathematical model to describe the PC behavior in a commercially available emitter. It is a 2D model that explains the relationship between the pressure, structural deformation and fluid flow within a PC emitter. A parametric study has been performed to understand the effects of geometric and material parameters with regards to the activation pressure and PC behavior. This knowledge will help guide the designs and prototypes of optimized emitters with a lower activation pressure, while also providing the PC behavior.Copyright

Modeling the future of irrigation: A parametric description of pressure compensating drip irrigation emitter performance

Drip irrigation is a means of distributing the exact amount of water a plant needs by dripping water directly onto the root zone. It can produce up to 90% more crops than rain-fed irrigation, and reduce water consumption by 70% compared to conventional flood irrigation. Drip irrigation may enable millions of poor farmers to rise out of poverty by growing more and higher value crops, while not contributing to overconsumption of water. Achieving this impact will require broadening the engineering knowledge required to design new, low-cost, low-power drip irrigation technology, particularly for poor, off-grid communities in developing countries. For more than 50 years, pressure compensating (PC) drip emitters—which can maintain a constant flow rate under variations in pressure, to ensure uniform water distribution on a field—have been designed and optimized empirically. This study presents a parametric model that describes the fluid and solid mechanics that govern the behavior of a common PC emitter architecture, which uses a flexible diaphragm to limit flow. The model was validated by testing nine prototypes with geometric variations, all of which matched predicted performance to within R2 = 0.85. This parametric model will enable irrigation engineers to design new drip emitters with attributes that improve performance and lower cost, which will promote the use of drip irrigation throughout the world.

The Determination of Formation Number for Starting Buoyant Jets

Starting buoyant jets are widely observed in nature as well as in engineering applications. The interactions between the leading vortex ring and the trailing stem play a significant role on the development of the staring processes, and the Formation Number is established to be the criterion that demarcates the presence of the trailing stem and thus, the occurrence of pinch‐off. In this study, the buoyant formation number for a starting buoyant jet which includes the momentum inducement due to presence of buoyancy is examined numerically. The investigation is based on the results of a series of numerical simulations with the Large‐Eddy Simulation (LES) approach to reproduce the starting buoyant jet in a wide range of conditions from pure jets to lazy plumes. Based on the results, the buoyant formation number can be obtained following the occurrence of a step‐jump in the vortex ring circulation in the following manner. First, the vorticity is integrated through the half central plane of the computational do...