Carlos Santolaria

Numerical Simulation of the Dynamic Effects Due to Impeller-Volute Interaction in a Centrifugal Pump

We show the capability of a numerical simulation in capturing the dynamic and unsteady flow effects inside a centrifugal pump due to the impeller-volute interaction. The object of the study is a commercial centrifugal water pump with backward curved blades, which is built within a vaneless single tongue volute. For the numerical simulation, the viscous Navier-Stokes equations are handled with an unsteady calculation and the sliding mesh technique is applied to take into account the impeller-volute interaction. In keeping the unsteady terms of the equations active it is possible to correctly simulate the effects of the blade passage in front of the tongue and both the flow and pressure fluctuations induced. Time averaged numerical results are compared with the experimental performance curve. The numerical flow analysis allows the study of different variables which are always difficult to measure experimentally. The dynamic variables obtained with the proposed numerical model are compared with the experimental data

Unsteady flow structure and global variables in a centrifugal pump

A relationship between the global variables and the dynamic flow structure numerically obtained for a low specific speed centrifugal pump is presented in this paper. A previously developed unsteady flow model is used to correlate the dynamic field with the flow characteristics inside the impeller and volute of a single-stage commercial pump. Actually, the viscous incompressible Navier-Stokes equations are solved within a 3D unsteady flow model. A sliding mesh technique is applied to take into account the impeller-volute interaction. After the numerical model has been successfully compared with the experimental data for the unsteady pressure fluctuations pattern in the volute shroud, a new step is proposed in order to correlate the observed effects with the flow structure inside the pump. In particular, the torque as a function of the relative position of the impeller blades is related to the blades loading, and the secondary flow in the volute is related to the different pressure patterns numerically obtained. Local flow analysis and qualitative study of the helicity in different volute sections is performed. The main goal of the study presented is the successful correlation of local and global parameters for the flow in a centrifugal pump. The pressure forces seem to be the main driven mechanism to establish the flow features both in the impeller and volute, for a wide range of operating conditions.

Steady and Unsteady Radial Forces for a Centrifugal Pump With Impeller to Tongue Gap Variation

Experimental and numerical studies are presented on the steady and unsteady radial forces produced in a single volute vaneless centrifugal pump. Experimentally, the unsteady pressure distributions were obtained using fast response pressure transducers. These measurements were compared with equivalent numerical results from a URANS calculation, using the commercial code FLUENT. Two impellers with different outlet diameters were tested for the same volute, with radial gaps between the blade and tongue of 10.0% and 15.8% of the impeller radius, for the bigger and smaller impeller diameters, respectively. Very often, pump manufacturers apply the similarity laws to this situation, but the measured specific speeds in this case were found to be slightly different. The steady radial forces for the two impellers were calculated from both the measured average pressure field and the model over a wide range of flow rates in order to fully characterize the pump behavior. The data from the pressure fluctuation measurements were processed to obtain the dynamic forces at the blade passing frequency, also over a wide range of flow rates

Development of a predictive maintenance system for a centrifugal pump

An approach is presented for the development of a predictive maintenance system for rotor‐dynamic pumps, which focuses on the diagnosis of abnormal events related to fluid‐dynamic operating conditions. This methodology is based on an experimental characterization of the dynamic response of the pump under different loads and operation anomalies. The procedure has been put into practice on a medium‐sized centrifugal pump. The results obtained show that a simple spectral analysis of the pressure signals captured at either the inlet or the outlet of the pump can provide sufficient decision criteria to constitute the basis for a diagnostic system. This was not true however when analyzing signals of acceleration at the pump casing.

Angular Range and Uncertainty Analysis of Nonorthogonal Crossed Hot Wire Probes

Crossed hot wire probes are widely used for measuring two-dimensional flows. Many applications in fluid mechanics like turbomachinery require an angular range as large as possible and a reasonable uncertainty in both direction and velocity values. The classic design places the wires orthogonally, while an angle between the probe wires allows a wider angular range to be obtained. We show an experimental and a theoretical study of the response of this kind of probes, by analyzing the dependence of the calibration procedure and uncertainties of flow angle and velocity with the angle between the wires

Numerical Model for the Unsteady Flow Behaviour Inside a Double Suction Pump

The fluid flow inside a single stage double aspirating pump has been studied using a three-dimensional unsteady numerical model. The main goal is the validation of the numerical procedure proposed and the flow-field analysis at the whole stage. The URANS equations have been solved using a sliding mesh unsteady model, which is able to model the real movement of the impeller inside the volute. The equations have been considered both in the rotating frame for the impeller and in the absolute reference frames, for the inlet and volute sections. Therefore, unsteady effects and dynamic interactions are captured. Mesh independency studies have been carried out and the usual turbomachinery boundary conditions have been imposed. Once the model was validated through performance curve comparison, the flow patterns in the impeller, volute and suction regions have been investigated. Particularly, the suction flow field is of special interest due to induced distortion of the axial and circumferential velocity fields. Besides that, the pressure evolution is also considered in order to study the different patterns at the inlet of the pump, where cavitation is likely to arise. The flow at the suction of this pump is characterized by the existence of a particular geometry that tries to force a uniform flow for nominal flow rate. However, this geometrical configuration produces a strong distortion for off-design conditions. This lack of uniformity produces an unsteady incidence that gives rise to strong loading variations. The study of the evolution of such unsteadiness of the inlet flow throughout the impeller and the volute was also carried out. Even at nominal flow rate, some non uniformities are detected in the pressure distribution at the inlet, that may be caused by the geometrical arrangement of this part of the inlet casing. Instantaneous and averaged pressure fields are studied.Copyright

Measurements in the Dynamic Pressure Field of the Volute of a Centrifugal Pump

This paper presents an experimental investigation into the dynamic pressure field existing in the volute of an industrial centrifugal pump in order to characterize the interaction phenomena between impeller and volute. For that purpose, pressure signals were obtained simultaneously at different points of the volute casing by means of two miniature fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the passing blade frequency, regarding both amplitude and phase delay relative to a reference point. The analysis of the dependence of the pressure fluctuations on both flow-rate and position along the volute clearly indicates the leading role played by the tongue in the impeller-volute interaction and the increase of the amplitude of the dynamic forces in off-design conditions.

Unsteady Flow Structure on a Centrifugal Pump: Experimental and Numerical Approaches

Both experimental and numerical studies of the unsteady pressure field inside a centrifugal pump have been carried out. The unsteady patterns found for the pressure fluctuations are compared and a further and more detailed flow study from the numerical model developed will be presented in this paper. Measurements were carried out with pressure transducers installed on the volute shroud. At the same time, the unsteady pressure field inside the volute of a centrifugal pump has been numerically modelled using a finite volume commercial code and the dynamic variables obtained have been compared with the experimental data available. In particular, the amplitude of the fluctuating pressure field in the shroud side wall of the volute at the blade passing frequency is successfully captured by the model for a wide range of operating flow rates. Once the developed numerical model has shown its capability in describing the unsteady patterns experimentally measured, an explanation for such patterns is searched. Moreover, the possibilities of the numerical model can be extended to other sections (besides the shroud wall of the volute), which can provide plausible explanations for the dynamic interaction effects between the flow at the impeller exit and the volute tongue at different axial positions. The results of the numerical simulation are focused in the blade passing frequency in order to study the relative effect of the two main phenomena occurring at that frequency for a given position: the blade passing in front of the tongue and the wakes of the blades.Copyright

Hot Wire Measurements During Rotating Stall in a Variable Pitch Axial Flow Fan

This work deals with a series of experiments on the influence of the blade pitch on the rotating stall phenomenon in an industrial variable pitch, low-speed axial flow fan with low hub-to-tip ratio.Two simple hot wires were used to detect the rotating stall. One in the absolute frame and the other in the relative frame rotating with the rotor. The rotating stall features were determined, ranging from the non-existence in the whole flow range with the lowest pitch tested to one and two flow cells with the greatest pitch.Then, a triple hot wire, calibrated by a direct method, was used to measure the absolute flow field upstream and downstream from the rotor, before and during rotating stall for five distinct blade pitches. These measurements allow us to characterize different rotating stall structures.To understand the phenomena better, some tests were carried out in the relative frame, with the probe rotating with the rotor. An intermediate blade pitch with a single rotating cell was selected and measurements were taken at three radial positions. Velocity maps for all these measurements are presented.Copyright

Blade Pitch Influence at the Exit Flow Field of an Axial Flow Fan

Variable pitch axial flow fans are widely used in industrial applications to satisfy variable operating conditions. In this work, an experimental research on a fan of this kind has been carried out. The performance curves of the fan have been obtained and the flow field has been measured at the best efficiency point of each blade pitch tested and for a lower and higher flow rate, in a fixed plane downstream the rotor with a triple hot-wire probe. The radial and circumferential distributions have been obtained, and maps of the velocity components over a blade channel are shown for each operating condition. The flow structure, including the tip and hub blockage, the blade wakes and the main flow core, is characterized.Copyright