Zafer Bozkus

Reduction of scouring depth by using inclined piers

The aim of this experimental study is to examine the effect of inclination of dual bridge piers on scour depth under clear-water conditions for various uniform flow depths. Duration of 4 h was used in the experiments for each run. Scour depths were measured at four different points around the piers. The depths of local scour around inclined piers were found to be substantially smaller than the scour depths around vertical piers. Dimensional and nondimensional curves were developed and presented to show the variation of scour depth with relevant parameters obtained in the dimensional analysis. Results of the study were compared to those obtained from a similar study performed with single inclined piers to see the effect of the second pier on scour depths. Useful equations for the design engineers were developed based on multiple regression analyses, to be used for predicting local scour depths around vertical and (or) inclined piers in uniform and (or) nonuniform sediments. Normalized scour depths measured...

Dynamic force on an elbow caused by a traveling liquid slug

The impact force on an elbow induced by traveling isolated liquid slugs in a horizontal pipeline is studied. A literature review reveals that the force on the elbow is mainly due to momentum transfer in changing the fluid flow direction around the elbow. Therefore, to accurately calculate the magnitude and duration of the impact force, the slug arrival velocity at the elbow needs to be well predicted. The hydrodynamic behavior of the slug passing through the elbow needs to be properly modeled too. A combination of 1D and 2D models is used in this paper to analyze this problem. The 1D model is used to predict the slug motion in the horizontal pipeline. With the obtained slug arrival velocity, slug length and driving air pressure as initial conditions, the 2D Euler equations are solved by the smoothed particle hydrodynamics (SPH) method to analyze the slug dynamics at the elbow. The 2D SPH solution matches experimental data and clearly demonstrates the occurrence of flow separation at the elbow, which is a typical effect of high Reynolds flows. Using the obtained flow contraction coef?cient, an improved 1D model with nonlinear elbow resistance is proposed and solved by SPH. The 1D SPH results show the best fit with experimental data obtained so far.

Experimental and Numerical Analysis of Transient Liquid Slug Motion in a Voided Line

In this paper, the hydrodynamics of a single transient slug in a voided line was investigated numerically and experimentally. In the experiments, the liquid slugs of various lengths were propelled into an inclined smooth steel pipe under several different driving air pressures. The pipe segment terminates in an open ended elbow; the pressure time histories are recorded at this elbow. The recorded peak pressures are correlated to the tank pressures and pipe and slug geometry. Dimensionless parameters are developed to present the experimental data. Moreover, the flow is investigated numerically using several Godunov type schemes, namely, basic Godunov Scheme, Total Variation Diminishing (TVD), based Weighted Average Flux (WAF) method and two different Monotone Upstream Schemes for Conservation Laws (MUSCL) methods. These schemes employ Godunov s approach facilitating exact and Harten, Lax and van Leers modified approximate solver (HLLC) type solution methods solving the Riemann problem of gas dynamics equations. Furthermore, the recorded peak pressures at the elbow are compared with the results of the numerical analysis and results of two earlier studies.

Improved One-Dimensional Models for Rapid Emptying and Filling of Pipelines

Improved one-dimensional (1D) models ? compared to previous work by the authors ? are proposed which are able to predict the velocity, length and position of the liquid column in the rapid emptying and filling of a pipeline. The models include driving pressure and gravity, skin friction and local drag, and holdup at the tail and gas intrusion at the front of the liquid column. Analytical and numerical results are validated against each other, and against experimental data from a large-scale laboratory setup.

Comparison of Performance of Two Run-of-River Plants during Transient Conditions

AbstractWater hammer is an unsteady hydraulic problem commonly found in closed conduits of hydropower plants, water distribution networks, and liquid pipeline systems. Because of either a malfunction of a system or inadequate operation conditions, a pipeline may collapse or burst erratically, resulting in substantial damages and human loss in some cases. Therefore, it is crucial that engineers design and/or analyze projects with reliable computing methods for all foreseeable operation situations. In this paper, transient flow situations in run-of-river plants are investigated for various operation conditions such as load rejection, load acceptance, and instant load rejection. A computer program using the method of characteristics is used in two case studies having Pelton and Francis turbines, respectively. On the basis of the field data of the plants, their computational models are set up, and resulting transient pressures are computed and compared with available measured pressures. Comparisons indicate t...

An Improved 1D Model for Liquid Slugs Travelling in Pipelines

An improved one-dimensional (1D) model — compared to previous work by the authors — is proposed which is able to predict the acceleration and shortening of a single liquid slug propagating in a straight pipe with a downstream bend. The model includes holdup at the slug’s tail and flow separation at the bend. The obtained analytical and numerical results are validated against experimental data. The effects of the improvement and of holdup are examined in a parameter variation study.Copyright

A New Method for Prediction of the Transient Force Generated by a Liquid Slug Impact on an Elbow of an Initially Voided Line

The aim of the present study is to predict the impact force applied by an individual transient liquid slug on an elbow at the end of a horizontal and initially empty pipeline. The liquid slug is driven by pressurized air in a tank located upstream of the pipeline. The time dependent pressure distribution along the elbow and a vertical extension segment after the elbow are solved with a 1D numerical approach along a curved line mesh. An assumed and calibrated axial turbulent velocity profile function with 3D skewed shape for the slug is also used in the solution. The impact pressures and the transient forces at the elbow are computed and also compared with those obtained experimentally and numerically from previous studies. Comparisons indicate that the new method developed in the present study predict the peak pressures and/or forces with higher accuracy than the previous method proposed by other researchers.

EXPERIMENTAL INVESTIGATION OF SCOURING AROUND INCLINED BRIDGE PIERS

For a safe design of a bridge pier footing, it is important to estimate the maximum depth of scour as accurately as possible. The aim of this experimental study is to investigate the effect of an inclination of bridge piers on the development of the local scour depths around the bridge piers. The experiments were performed with single circular piers inclined towards the downstream direction making an angle with the vertical plane over uniform bed material under clear water conditions. Non-dimensional scour curves were developed to illustrate the temporal variation of the scour depth. The results of the present study were compared with those obtained using vertically mounted piers by the previous investigators. The depth of local scour around inclined piers was observed to be smaller than that of the case of the vertically mounted piers.

Prediction of pressure variation at an elbow subsequent to a liquid slug impact by using smoothed particle hydrodynamics

Liquid slug flow driven by pressurized air in an inclined pipe with a downstream elbow is investigated numerically. As the liquid slug hits the elbow, the impact pressure and the associated force generated at the elbow may damage pipe supports as well as the pipe itself. It is essential for the design engineers of pipeline systems to accurately predict the pressure trace during the impact for safe operation. The slug arrival velocity and slug length (i.e., mass) at the elbow directly affect that pressure. In order to calculate these slug parameters just before the impact, an improved one-dimensional (1D) model proposed in the literature is used. At the elbow, pressure variation with respect to time is calculated by a recently developed computer code which uses a two-dimensional (2D) smoothed particle hydrodynamics (SPH) method. In the numerical setup, two representative initial slug lengths, one for short slugs and one for long slugs, and three different initial air tank pressures are used. The obtained numerical data are validated with available experimental results. For both short and long slugs, calculated peak pressures show great agreement with measured peak pressures.

Modeling liquid slugs accelerating in inclined conduits

In this article, we simulate traveling liquid slugs in conduits, as they may occur in systems carrying high-pressure steam. We consider both horizontal and inclined pipes in which the slug is accelerated by a suddenly applied pressure gradient, while at the same time, gravity and friction work in the opposite direction. This causes a steep slug front and an extended slug tail. The shapes of front and tail are of interest since they determine the forces exerted on bends and other obstacles in the piping system. The study also aims at improving existing one-dimensional (1D) models. A hybrid model is proposed that enables us to leave out the larger inner part of the slug. It was found that the hybrid model speeds up the two-dimensional (2D) computations significantly, while having no adverse effects on the shapes of the slugs front and tail.