Ivar Annus

Experimental investigation on rapid filling of a large-scale pipeline

This study presents the results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water-level meters, thermometers, void fraction meters, and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water-air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made.

Emptying of large-scale pipeline by pressurized air

AbstractEmptying of an initially water-filled horizontal PVC pipeline driven by different upstream compressed air pressures and with different outflow restriction conditions, with motion of an air-water front through the pressurized pipeline, is investigated experimentally. Simple numerical modeling is used to interpret the results, especially the observed additional shortening of the moving full water column due to formation of a stratified water-air “tail.” Measured discharges, water-level changes, and pressure variations along the pipeline during emptying are compared using control volume (CV) model results. The CV model solutions for a nonstratified case are shown to be delayed as compared with the actual measured changes of flow rate, pressure, and water level. But by considering water-column mass loss due to the water-air tail and residual motion, the calibrated CV model yields solutions that are qualitatively in good agreement with the experimental results. A key interpretation is that the long air...

Controlling Stormwater Runoff from Impermeable Areas by Using Smart Inlets

Climate change and rapid urbanization are driving the need for improved urban stormwater runoff strategies. Urban stormwater drainage systems are severely affected by the changing climate bringing along inter alia more intense rainfall events. The pipeline system, usually having limited capacity, is unable to cope with these excessive flows and becomes surcharged. This may trigger overland flow from the drainage manholes and activate combined sewer overflows. Both events have negative consequences and therefore should be avoided. There are available effective solutions, like low impact development techniques for the catchments under development. However, options for retrofitting the existing drainage facilities are much more limited. Enlarging the pipelines, which has been a traditional response for rising demands is often financially unrealistic due to the large scope of the work. Therefore, recent advances in “smart” water system technologies are considered as an opportunity to meet the future challenges. In this study the concept for controlling stormwater outflow from impervious catchment areas, i.e. parking lots is developed. The target is to find a solution that is affordable and can be implemented with minor disturbances in the area. For that, a novel approach of controlling water flow by regulating the inflow to the manholes is analysed. The adjustable gullies are real time controlled by coupling rule-based algorithms with distributed model predictive control. The concept is successfully tested in a 12 ha impervious catchment area in Tallinn.

Modelling of nitrogen leaching from watersheds with large drained peat areas

Abstract The SOIL and MACRO models with different versions of SOILN initially developed for small field-scales were used to simulate the water flow and nitrate N concentrations in two watersheds in Estonia that contain large areas of peat soils. Monitoring data show that nitrogen concentrations tend to increase in some rivers even where the human activity is very low. This may be connected to soil self-degradation processes taking place in drained peat soils where it is difficult to use most of the hydrological models. Results show that SOIL, MACRO and SOILN may be successfully applied at the watershed scale to model the water quantity and quality on watersheds with high content of peat soils. The analysis revealed that the nitrate nitrogen level trends depend considerably on the meteorological conditions.

USING TRANSIENT FLOW EQUATIONS FOR MODELLING OF FILLING AND EMPTYING OF THE LARGE-SCALE PIPELINE

The transient flow equations are often employed to model unsteady two-phase flow in pressurized systems. In present study the parametric perturbation technique is used to deal with the flow transients in cases of filling and emptying of large-scale pipeline. The scaling Mach number and scaling Froude number are introduced to non-dimensionalize the transient flow equations for horizontal pipe. The rigid water-column flow case serves as the lowest order solution for the two-phase flow. The pressure wave effects generated due to valve closing/opening are represented as higher order corrections to the rigid water-column model. The standard numerical schemes are employed to calculate the two-phase flow in pipeline: 1) controlled filling of the pipeline and 2) controlled emptying of the pipeline. It is also demonstrated that the higher-order equations of used perturbation scheme yield the water hammer results with some simplifications.