Adam Adamkowski

Experimental Examination of Unsteady Friction Models for Transient Pipe Flow Simulation

The paper presents a comparative analysis of calculations performed basing on the selected unsteady friction models and their validation based on the results of own experimental tests. The computer code developed for predicting transient pipe flows includes the models of: Zielke, Trikha, Vardy and Brown, Zarzycki, and Brunone et al. Our own experiments have been conducted at a test rig designed and constructed at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences (IMP PAN) in Gdansk in order to test transient pipe flows in a wide range of Reynolds numbers. The results following from this analysis enable the quantitative and qualitative assessment of the models under consideration. DOI: 10.1115/1.2354521

Investigation of Hydraulic Transients in a Pipeline with Column Separation

The authors previously described a new method [based on the new discrete vapor cavity model (new DVCM)] for numerical prediction of pressure changes during the water hammer with liquid column separation together with results of preliminary experimental verification of this method. This paper is a continuation of the research and includes results of additional laboratory tests and visualization of the cavitation zones generated during transient flow with liquid column separation. The results of these studies provide a better understanding of the phenomenon. It is shown that the phenomenon can have a distributed nature, which means that gas-vapor zones may be observed not only locally, in the vicinity of the shutoff valve, but may be spread along the pipeline length, and the intensity of this phenomenon decreases with distance from the valve. Laboratory test results were also used for further verification of the new DVCM. This verification shows that agreement between calculated and experimental results strongly depends on the friction model incorporated into the calculation. This agreement also depends on the intensity of liquid column separation: for cases of severe separation, the differences between numerical and measured pressure changes are small and accepted from the practical point of view.

A New Method for Numerical Prediction of Liquid Column Separation Accompanying Hydraulic Transients in Pipelines

This paper presents a new method for calculating pressure fluctuations in pipelines during a water hammer with liquid column separation. The method is based on the discrete-vapor-cavity model (DVCM). Such kind of models assumes that vaporous cavities are formed in each computational section of the pipeline whenever the pressure drops to the vapor pressure at a given temperature. The proposed new model (new DVCM) brings a significant improvement in the reliability of predictions compared with existing DVCMs. The calculation method based on it eliminates some disadvantages of basic methods used in practice, as shown by comparisons between calculations made for simple hydraulic system under theoretical frictionless conditions using various DVCMs. Additionally, the authors present preliminary verification of the proposed model based on experimental results. The positive results of this verification, and the advantages of the new DVCM, could lead to incorporating them into commercial codes.

Cavitation Characteristics of Shutoff Valves in Numerical Modeling of Transients in Pipelines with Column Separation

AbstractThe paper presents the results of calculations of the water-hammer course accompanied by the column separation caused by a rapid closure of the inline valve. The most important problem which the paper is dealing with is taking into account the cavitation characteristics of the inline valve. The calculation method contains a special way of including valve characteristics that have been determined on the laboratory setup in the Szewalski Institute of Fluid-Flow Machinery (IFFM) in Gdansk, Poland. In addition, calculations have been conducted using the writers’ own discrete vapor cavity model (DVCM), the new single-zone DVCM. The paper presents a comparison between these calculation results and the experimental results obtained at the laboratory setup for investigation of the water-hammer phenomenon in the pump discharge pipeline. The comparison of the numerical and empirical results is a basis for the verification process and assessment of the computational method that has been developed. The result...

Improved Discharge Measurement Using the Pressure-Time Method in a Hydropower Plant Curved Penstock

One of the basic flow rate measurement methods applied in hydropower plants and recommended by the International Standard IEC 60041―1999 and American National Standard ASME PTC 18―2002 is the pressure-time method, generally known as Gibson method. The method consists in determining the flow rate (discharge) by integration of the recorded time course of pressure difference variations between two cross sections of the hydropower plant penstock. The accuracy of measurement depends on numerous factors and, according to the International Standard, generally is confined within the range 1.5―2.3%. Following the classical approach, the pressure-time method applicability is limited to straight cylindrical pipelines with constant diameters. However, the International Standard does not exclude application of this method to more complex geometries, i.e., curved pipeline (with elbows). It is obvious that a curved pipeline causes deformation of the uniform velocity field in pipeline cross sections, which subsequently causes aggravation of the accuracy of the pressure-time method flow rate measurement results. The inffuence of a curved penstock application on flow rate measurements by means of the considered method is discussed in this paper. The special calculation procedure for the problem solution has been developed. The procedure is based on the FLUENT computational fluid dynamic solver. Computations have been carried out in order to find the so-called equivalent value of the geometric pipe factor F required when using the pressure-time method. An example of application of this method to a complex geometry (two elbows in a penstock) is presented. The systematic uncertainty caused by neglecting the effect of the elbows on velocity field deformation has been estimated.

Special Instrumentation and Hydraulic Turbine Flow Measurements Using a Pressure-Time Method

The objective of the work was to evaluate the efficiency of a hydraulic turbine by means of the flow measurement, for a given water head. The hydraulic turbine of 180 MW output has been in service for 20 years. The real value of efficiency was needed in order to proceed with minor/mayor modifications to improve it. In a case of a runner deterioration the pressure-time (the Gibson) method was chosen to proceed with a test for flow determination. However, to measure the pressure in the penstock no access from the external space of the penstock was found, so the special instrumentation had to be developed, which could be installed inside different sections of the penstock for determination of the pressure as required by the Gibson method. After the successful installation of the pressure transducers and a special hermetic capsule, from which a cable was laid through the manhole to the control room, the test was carried out at different loads applying the Gibson method. Simultaneously, the instrumentation for the Winter-Kennedy method was installed and calibrated during the test. In the paper all the turbine measured characteristics are given and discussed. It was concluded that the efficiency of the hydraulic turbine was still high and no modifications were necessary. Having instruments calibrated for the Winter-Kennedy method other curves can be obtained at different heads.Copyright

Experimental Investigation of Dynamic Characteristics of Swing and Tilted Disc Check Valves

The present work describes an experimental investigation of the dynamic characteristics of check valves, which means experimental examination of closing function and ability to generate pressure transients under different flow decelerations in the pipeline. Two designs of check valves are tested: a swing disc and a tilted disc check valve.The valves are mounted on discharge pipe of a centrifugal pump. The fluid transient is generated by stopping the pump motor from actual velocity to completely stop in a prescribed time.Each of the check valves is subjected to tests covering different pressure levels in the upper reservoir, initial flow rates in the pipeline, several decelerations of pump rotation, three settings of torque acting on the valve disc, three values of the moment of friction forces acting on the valve axis and finally free fall of the disc in stagnant water and air.The test stand, the instrumentation and chosen valves as well as scope and conditions for performing the experiments are described. Selected measured results like angular velocities of the discs, pressures in the pipe at different conditions, and volumetric flow rates are presented and discussed.The dynamic behaviors of the tested valves were compared with each other.Copyright

New Method for Numerical Prediction of Water Hammer With Column Separation: Comparison With Experiment and the Relap5 Program

Liquid column separation accompanying water hammer (hydraulic transients) was a subject of numerous research works conducted in many scientific centres of the world. So far, there are not any satisfactory results of using computational methods to simulate this phenomenon. The authors of this paper have developed a new method for calculating pressure fluctuations in pipelines during hydraulic transients with liquid column separation. This method is based on the innovative (original) discrete-vapour-cavity model. In the paper there are two steps presented in the validation process of the new model. The first step is the comparison with experimental data and the second one is the comparison with results obtained using the commercial computer program Relap5. The comparisons of calculated by means of the considered numerical methods and measured pressure surges show significant differences. The reasons for the discrepancies are discussed and conclusions are presented.© 2009 ASME

Elastic Water-Hammer Theory–Based Approach to Discharge Calculation in the Pressure-Time Method

AbstractAn original numerical procedure based on the elastic water-hammer theory, with special solutions of continuity and momentum equations modeling the unsteady liquid flow in pipelines, has bee...

The Effect of Boundary Layer Separation on Accuracy of Flow Measurement Using the Gibson Method

The Gibson method utilizes the effect of water hammer phenomenon (hydraulic transients) in a pipeline for flow rate determination. The method consists in measuring a static pressure difference, which occurs between two cross-sections of the pipeline as a result of a temporal change of momentum from t0 to t1 . This condition is induced when the water flow in the pipeline is stopped suddenly using a cut-off device. The flow rate is determined by integrating, within a proper time interval, the measured pressure difference change caused by the water hammer (inertia effect). However, several observations demonstrate that changes of pipeline geometry like diameter change, bifurcations, or direction shift by elbows may produce an effect on the computation of the flow rate. The paper focuses on this effect. Computational simulations have shown that the boundary layer separates when the flow faces sudden changes like these mentioned to above. The separation may reduce the effective cross section area of flow modifying a geometry factor involved into the computation of the flow rate. The remainder is directed to quantify the magnitude of such a factor under the influence of pipeline geometry changes. Results of numerical computations are discussed on the basis of how cross section reductions impact on the geometry factor magnitude and consequently on the mass flow rate.Copyright