Influence of the Blade Design Parameters on Hydraulic Noise Generation by a Low Specific Speed Radial Pump With Narrow Channel Flow

Present work aims to investigate the hydro acoustic behavior of a typical low specific speed radial type centrifugal pump with narrow channel impeller passage. The blade design parameters play an important role in hydraulic noise generation by a low specific speed radial pump with narrow impeller channels. Though, these pumps are hydraulically efficient for a given design point, the hydraulic noise production may be higher at duty point. The blade passage length along with the outlet width of the impeller are the two main design parameters of a radial impeller with narrow channels, which can impact the flow quality along the impeller blade passage. To understand the effect of the narrow channel, initially steady state simulation is conducted to predict and validate the hydraulic performance. Then transient simulations were conducted using Detached Eddy Simulation (DES) using STAR-CCM+ to predict the hydro acoustic behavior of the pump in terms of pressure fluctuations and far field noise spectra of the pump at specific points. The velocity profiles along the impeller channels, shows the formation of wake region, which strongly affects the jet wake flow phenomenon near impeller trailing edge. This results in high pressure fluctuations near impeller outlet.

Impact of Skew Vane Cut on Alternating Stress in a Low Specific Speed Radial Pump Impeller Vane Using Fluid-Structure Interaction (FSI) Simulations

Numerical studies are presented on the pressure pulsations, hydraulic excitation forces and alternative stresses produced in a radial volute pump with high head application. The effect of excitation forces due to Rotor-Stator Interaction (RSI) are evaluated using One-way fluid structure Interaction in terms of alternative stresses on impeller pressure side and suction side. Initially, the pump performance parameters are predicted using steady state Computational Fluid Dynamics (CFD) simulations and compared with the available test data. Due to the transient behavior of pressure pulsations, a transient CFD simulation has been conducted using RANS models to predict the pressure pulsations and its behavior with time on impeller vane outlet and tongue locations. These unsteady pressure distributions are further coupled with the Finite element (FE) model of the impeller to solve and monitor for the stresses induced due to the transient hydraulic loading. To attenuate the alternating stresses produced due to RSI, the geometry of the vane is modified by providing a skew cut with 30° at vane outlet. The pressure pulsation amplitude and stresses are reduced by 10% and 10% respectively for a skew cut of 30° at vane trailing edge.

Numerical study on the transient behavior of a radial pump during starting time

This paper presents a fast simulation model for predicting the dynamic response of a motor-pump system to startup event. The purpose is to analyze the effect of the impeller acceleration time, the final flow rate and the impeller geometry on the pump transient flow during starting operations. The motor speed and torque variations were predicted by simulating the transient law of the three-phase induction motor by adopting the d-q axes theory. The pump model was built by solving the unsteady flow governing equations with the method of characteristics (MOC). The whole model was validated with available tests from literature. Accordingly, the computation of impeller acceleration, the motor torque, the unsteady pressure and flow rate was made for various starting conditions. The results have revealed that during its starting time, the pump hydraulic transients are well influenced by the motor speed acceleration, the flow inertia and the impeller geometry. Through the analysis of the simulation results, the conclusion was that the accuracy of the present method is reasonable, and it can be used for assisting pumping system design.

Validation of the Axial Thrust Estimation Method for Radial Turbomachines

The fast preliminary design and safe operation of turbomachines require a simple and accurate prediction of axial thrust. An underestimation of these forces may result in undersized bearings that can easily overload and suffer damage. While large safety margins are used in bearing design to avoid overloading, this leads to costly oversizing. In this study, the accuracy of currently available axial thrust estimation methods is analyzed by comparing them to each other and to theoretical pressure distribution, numerical simulations, and new experimental data. Available methods tend to underestimate the maximum axial thrust and require data that are unavailable during the preliminary design of turbomachines. This paper presents a new, simple axial thrust estimation method that requires only a few preliminary design parameters as the input data and combines the advantages of previously published methods, resulting in a more accurate axial thrust estimation. The method is validated against previously public data from a radial pump and new experimental data from a centrifugal compressor, the latter measured at Lappeenranta-Lahti University of Technology LUT, Finland, and two gas turbines measured at Aurelia Turbines Oy, Finland. The maximum deviation between the estimated axial thrust using the hybrid method and the measured one is less than 13%, while the other methods deviate by tens of percent.

Impact of Interface Model on Simulation Results of a Radial Pump at Part Load and Shut-Off Conditions

Computational Fluid Dynamics (CFD) is a well-known tool for predicting and analyzing performance in a variety of engineering branches, including turbomachinery, allowing engineers to partially replace physical experiments with their virtual analog. Nevertheless, numerical analysis should be used carefully regarding possible deviation between simulated and experimental results due to multiple reasons (including but not limited to applied simplifications in the numerical model). These deviations usually have their minima close to the Best Efficiency Point (BEP). The paper deals with analyzing the outcome of steady-state simulations for a radial pump at strong part load and shut-off conditions by switching between three simulation types (steady-state with mixing plane, steady-state with frozen rotor, transient with sliding mesh). A comparison of velocity profiles on the interface surfaces is made, showing how the chosen interface model affects the structures being formed at part load conditions. These effects show particular impact on performance parameters (first of all, head production), which is discussed in the paper. The information provided could be helpful for adjusting the simulation parameters and finding an appropriate compromise between simulation reliability and demand for computational time thereby.

Experimental study of the characteristic curves of 0.5 HP radial pump with constant speed

Radial (centrifugal) pumps are commonly used in industry and represent 22% of total consumption of the energy worldwide. The understanding of their operating conditions is important for a proper selection and use, specifically at the Best Efficient Point (BEP). This study analyzed the variation of the operating conditions of a common, small pump when the flow is regulated with a control valve at the pump discharge, keeping the rotational speed constant. The system consists in a closed loop using a turbine meter programmed in Arduino for flowrate measurement. The electric power and energy consumption were provided by an electronic Wattmeter, and the pressure at the suction/discharge of the pump was taken from Bourdon gauges. The minimum submergence of the pump intake was calculated with the Standard ANSI-HI-9.8 and the Bourdon gauges selection followed the recommendations of the Standard ASME B40.100-1998. All the measurements are part of the Energy equation for the pump-motor system (monoblock unit), whose H-Q curve is compared to manufacturer’s curve with reasonable agreement that served as validation. The electric power curve is the evidence that the flow regulation method is unappropriated because the power consumption increases as the flow is regulated. At the end, the efficiency curve of the motor-pump unit was presented, with a maximum value of 12%. The shock and recirculation losses are present, but the electrical losses are evidenced through excessive heating. The test bench will have a better pump and a variable frequency drive for further studies.

An Artificial Intelligence Based Method for Performance Prediction and Inverse Design of Hydraulic Turbochargers

A neural network based method is developed that can learn the underlying physics of hydraulic turbocharger (a radial pump coupled with a radial turbine) from a set of sparse experimental data and can predict the performance of a new turbocharger design for any given set of previously unseen operating conditions and geometric parameters. The novelty of the algorithm is that it learns the underlying physical mechanisms from a very sparse data spanning a broad range of flow rates and geometrical size brackets and uses these deeper common features recognized through a “mass-learning process” to predict the full performance curves for any given single geometry. The deep learning algorithm is able to accurately predict the key performance parameters like total efficiency of the turbocharger, its operating speed, pressure rise provided by the radial pump of the turbocharger and the shaft power produced by the radial turbine of the turbocharger for any given input combination of pump and turbine flow rates, differential pressure across the turbine and a limited set of geometrical parameters of pump and turbine impellers and volutes. Lastly, a novel method for fast inverse design of turbomachinery using a physics trained neural network and a constrained optimization algorithms is developed. The algorithm uses Nelder-Mead and Interior Point methods to find the global minimum of turbocharger design objective function in multi-dimensional space. The newly developed method is found to be very efficient in optimizing turbomachinery design problems with both equality and inequality constraints. The inverse design algorithm is able to successfully recommend an optimal combination of geometrical parameters like pump blade exit angle, pump impeller diameter, blade width, eye diameter, turbine nozzle diameter and rotational speed for a given target efficiency and head rise requirements. The preliminary results from this study indicate that it has a great potential to minimize the need for expensive 3D CFD based methods for the design of turbomachinery.

Simulation of a Radial Pump Fast Startup and Analysis of the Loop Response Using a Transient 1D Mean Stream Line Based Model

A predictive transient two-phase flow rotodynamic pump model has been developed in the Code for Analysis of THermalhydraulics during an Accident of Reactor and safety Evaluation (CATHARE-3). Flow inside parts of the pump (suction, impeller, diffuser and volute) is computed according to a one-dimensional discretisation following a mean flow path. Transient governing equations of the model are solved using an implicit resolution method and integrated along the curvilinear abscissa of the element. This model has been previously qualified at the component scale by comparison to an existing experimental database. The present study aims at extending the validation at the system scale: a whole experimental test loop is modelled. The ability of the transient pump model to predict flow rate, head and torque as a function of time during a 1-s pump fast start-up is evaluated. The transient evolution of the pressure upstream and downstream from the centrifugal pump is well predicted by the simulation compared to the measurements. Local quantities such as pressure and velocity inside elements of the circuit are analysed. In the considered case, inertial effects of the global circuit are dominant when compared to pump inertial effects due to the high characteristic lengths of the pipes. The main perspective of this work consists in the simulation of similar pump transients, in cavitating conditions.