Rotor-stator Interaction Research Articles

The Effects of Meridian Surface Shape on the Pressure Pulsation of a Multi-Stage Electric Submersible Pump

The influence mechanism of the internal pressure fluctuation propagation law of multi-stage submersible electric pump (ESP) is still unclear, which has been a major problem restricting the stable exploitation of deep-sea oil and gas. In order to investigate the effect of different meridian profiles on the pressure pulsation characteristics of three-stage submersible electric pumps, the unsteady Reynolds-averaged Navier–Stokes (URANS) method is used to numerically investigate it. The results show that the lower the pressure pulsation amplitude in the pump caused by the meridional shape that is more in line with the flow law, has a positive effect on the operation stability. The change of the shape of the meridian greatly affects the pressure pulsation law in the secondary and final pumps. The rotor–stator interaction causes the pressure pulsation amplitude of the monitoring point in the middle of the pump chamber to reach a peak value. By using continuous wavelet transform analysis, it is found that the regularity of 1–2 times frequency conversion is complicated due to multiple pulsation sources and low frequency propagation coupling between stages. At 3–6 times frequency, it is basically close to the pulsation rule of the blade frequency. The above research provides a basis for improving the operation stability of the ESP.

Pressure Fluctuation–Vorticity Interaction in the Volute of Centrifugal Pump as Hydraulic Turbines (PATs)

The pump as turbines (PATs) has been widely used in the petrochemical, seawater desalination, and mining industries. Volutes are critical components for flow guidance and energy conversion in the PATs. Therefore, its inner flow characteristic could significantly influence the hydraulic turbine system stability. To reveal the vortex evolution, pressure pulsation characteristics, and the interaction between the two in the volute of PATs, a single-stage cantilever hydraulic turbine is investigated by the numerical and experiment method. The effect of impeller rotation on vorticity distribution and pressure fluctuation intensity in volute is analyzed based on the numerical simulation results. By clarifying the frequency components corresponding to local high amplitude vorticity and pressure pulsations, the relationship between vortex evolution and pressure pulsations is established. The results showed that the dominant frequency of pressure pulsation in the circumferential direction of the volute is 6fn under different operating conditions, and the pressure pulsation characteristics in the inlet section of the volute were less affected by the rotor–stator interaction. Under Qb and 1.3Qb conditions, the vorticity pulsation near the walls in the circumferential direction of the volute had less effect on local pressure pulsation characteristics. The evolution of vorticity at the leading edge of the volute tongue intensified the local pressure pulsations as the flow rate increased. Under 0.7Qb conditions, the vorticity pulsation characteristics in the volute are complex and have a relatively significant influence on local pressure pulsation.

Dynamics of a non-linear Jeffcott rotor in supercritical regime

This work is concerned with the prediction and simulation of limit cycles of a nonlinear Jeffcott rotor. Geometrical nonlinearity (related to large flexural displacements) in both stiffness and internal damping is considered. Classical instabilities due to linear internal damping occurring in the supercritical range are modified by nonlinear effects and lead to oscillating limit cycles at a radius whose value is found analytically as a function of the rotating speed. If the rotor is additionally excited by unbalance, the response spectrum also contains the excitation frequency, and the bifurcation leads to quasi-periodic limit cycles. The dynamics of this system is studied numerically via the harmonic balance method, path continuation and bifurcation tracking. In particular, an original procedure for switching to a branch of quasi-periodic solutions is proposed. To preserve the integrity of the machine post bifurcation, one then considers the possibility of constraining the transverse displacement of the shaft. Such possible rotor–stator interaction generates three-frequency quasi-periodic oscillations. Frequency response curves show that the quasi-periodic solutions created by the bouncing rotor are mainly driven by the friction coefficient.

Toward a better understanding of synchronous vibrations in hydroelectric turbines

Runner–casing interactions are known to be major stress contributors during turbine operation in nominal regimes. These synchronous vibrations must be properly understood to ensure reliable long-term turbine operation. It is widely accepted in the hydro community that rotor–stator interactions (RSI) are the main runner–casing mechanisms. In this study, the authors demonstrate that casing non-uniformities can induce a wide range of synchronous vibrations in a hydroelectric turbine, that are not predicted by the standard RSI theory. The mathematical background that generalizes RSI concept is first derived and then the theory is verified using recorded data from two different hydroelectric Francis runners. The suggested framework is able to explain unexpected resonances between rotating speed harmonics and structural modes observed during runner transient operations.

Numerical investigation of the effect of axial clearance on the last stage of marine turbine

The axial clearance between the stationary and moving blade rows has a significant impact on the weight and volume of marine turbines, while excessively small clearance can lead to collisions between stator and rotor or even threaten the ship. To investigate the effects caused by axial clearance in marine turbines, a numerical simulation is performed on the last stage of a subsonic low-pressure turbine. The results show a significant effect of the axial clearance on the flow field. When the axial clearance increases, the pressure fluctuation amplitude on the blade surface decreases significantly, but the instability strengthens. There are many vortex structures at the blade root identified by the Q criterion. Vortex structures become smaller with the expanding axial gap, separating into multiple small vortex structures, which is the critical cause of instability. By FFT analysis, the change of axial gap mainly affects the blade passing frequency. Excessive axial clearance results in instability components in the spectrum because of the interaction of rotor-stator interaction and vortex structures in the flow field. The efficiency decreases slightly as the axial gap increases. This study provides a reference for the design of the axial clearance of the last stage of the marine turbine.

Performance Assessment of Tesla Expander Using 3D Numerical Simulation

Abstract Bladeless or Tesla turbines consist of several flat parallel disks mounted on a shaft with a narrow gap between them. The analytical solution of Navier-Stokes equations for the flow between disks has been extensively studied in the past. However, there is a significant impact of the stator exit-flow conditions on the performance and flow behavior inside the rotor of the Tesla turbine. There has been limited research on flow characterization and performance evaluation of stator-rotor interaction of the Tesla expander using 3D numerical simulation. The challenge arises due to a very high aspect ratio of the Tesla rotor (diameter to gap ratio > 1000). 3D numerical modeling with a hexahedral mesh of the nozzle/stator with the commercial software is presented. The simulation is performed for a wide range of inlet pressures and rotational speeds. This work focuses on the stator performance, the stator-rotor interaction, the rotor entry losses due to disk tip, the rotor tip velocity ratio and the degree of reaction on the performance of the Tesla expander.The peak efficiency of 58% is predicted for 3 bar inlet pressure and a rotational speed of 30000 rpm for a 3 kW machine with air as a working fluid. The 3D numerical analysis provides insights on flow characterization, mainly stator-rotor interaction and flow between disks at different mass flows. Numerical results are also compared with experimented test results performed on a 100-W and a 3-kW air expander.

Study of rotor–stator interaction phenomenon in a double-suction centrifugal pump with impeller vane trailing edge as a design parameter

Various geometrical parameters, such as cut-water clearance, volute tongue location, tongue radius, vane trailing edge profile, and flow parameters like speed and operating point, affect the rotor–stator interaction in a centrifugal pump. In the present investigation, vane trailing edge is selected as a design parameter for profile modifications to study and reduce the rotor–stator interaction intensity and hence the pressure pulsations. A double-suction centrifugal pump with tangential discharge volute (M1) and specific speed (ns) 19 has been selected for the numerical experiments. Transient analysis using detached eddy simulation is used for predicting flow parameter behavior at impeller periphery (primary source) and volute tongue locations (secondary source). The impeller periphery probes in the rotor–stator interaction zone are used to identify the intensity of the jet-wake flow phenomenon and its interaction with the volute tongue. Similar strategy has been applied by modifying the trailing-edge profile of the original geometry with vane underfiling (M2) and the M2 vane geometry with novel trailing-edge profile (M3). The pressure pulsation behavior along the impeller periphery (primary source) shows the strong reduction of pressure amplitude near volute tongue by 42% in M3 compared to M1 aligning with the reduction of jet-wake flow intensity. The pressure fluctuation (rms) near volute tongue (secondary source) shows an average reduction of 11% in modified trailing edge (M3) relative to M1. The intensified rotor–stator interaction due to vortex shedding in M2 causes relatively higher pressure fluctuations (rms) near volute tongue compared to M1 and M3.

Solving the challenging puzzle of the Grimsel II runner vibration

After 30 years of operation, the runners of the four 100 MW high-head Francis turbines successively developed fatigue cracks starting from the hub-side trailing-edge fillets. Assessment of alternating stress in normal turbine operation revealed that stress levels were not nearly large enough to explain the damages. Consequently, a test campaign comprising start and stop manoeuvres in addition to normal turbine operation was conducted in 2017. Strain gauge signals obtained on-board of the runner blades were recorded together with casing vibration and acoustic signals. Intense high-frequency vibration centred around 611 Hz was detected in three transient conditions of operation: at speed-no-load (SNL), during coast-down and during back-to-back pump start. Common properties of these conditions were very low to no discharge, strong secondary flow in the runner and speed between 50 and 100 %. Due to the extremely narrow bandwidth, three possible ways of excitation were considered and checked: rotor-stator interaction (RSI), rotor-dynamic instability and Von Kármán excitation. RSI was excluded due to speed-independent frequency. Strong sidebands in the stationary-frame frequency spectra - obviously caused by runner shroud deformation shapes ND1 through ND5 - excluded any feedback from runner side chamber pressure; thus leaving Von Kármán excitation as the only possible diagnosis. Accordingly, a very safe profile was selected and implemented for the runner blade trailing edges. Subsequent field-testing at two modified units confirmed that the vibration problem at the harmful operation points had hereby been eliminated.

Towards accurate vibration prediction of pump-turbine runners in deep partial load operation

Within the XFLEX HYDRO project, operating power plants in low load conditions is being investigated as one of the possibilities to enhance the flexibility of hydropower. Therefore, the structural dynamic behaviour of a pump-turbine runner is numerically analysed in deep partial load (DPL) operating points. Based on highly resolved unsteady CFD simulations performed prior to this work, the pressure fluctuations are extracted and mapped onto the structure for subsequent Finite Element (FE) analyses. Herein, an efficient hybrid methodology combining purely structural and coupled Fluid-Structure-Interaction (FSI) modelling is applied. The obtained simulation results are compared to experimental measurements. Herein, the influence of several factors such as the CFD mesh size, the turbulence model, the simulated time window width, and the structural simulation type is studied. As a result, the numerical outcome is validated with good accuracy. The importance of highly resolved CFD simulations with appropriate turbulence modelling is highlighted. Besides, the necessity of coupled acoustic-structural analyses to accurately resolve the dynamic response to excitation by rotor stator interaction (RSI) pressure shapes is demonstrated despite the chaotically dominated nature of the structural vibrations. The results of this work can be used to extend the operating range of the pump-turbine runner and, most importantly, to calibrate numerical models to predict the structural vibrations accurately and efficiently in DPL and finally ensure safe operation of these components.

Characterization of the hydrodynamic instabilities in a pump-turbine operating at part load in turbine mode

Pump-turbines (RPT) nowadays represents the most common mechanical equipment adopted in the new generation of storage hydro plant. In order to balance the frequent changes in electricity production and consumption caused by unpredictable renewable energy sources, RPT are forced to rapidly switch between the pumping and generating mode also extending their operation under off-design conditions in unstable operating areas. Because of the design criterion adopted for the development of a RPT, an unstable behavior represented by a typical S-shaped profile with a positive slope in the machine’s characteristic can occur near to the runaway condition.With the purpose of evaluating the evolution of the fluid field near to the no-load condition, an in-depth CFD analysis of the RPT model test of the Norwegian Hydropower Center is performed by retracing the machine’s characteristic curve running through the flow-speed characteristic curve up to the turbine brake region for fixed guide vanes opening. To validate the numerical results, a comparison with the experimental results in terms of characteristic curves and pressure signals is performed.The results allow to capture the 3D characteristics of the unsteady phenomena, progressively evolving in an organized rotating stall, highlighting also the influence of the flow rate change from partial loads to the turbine brake operation on their development. In order to characterize the pulsating nature of the instability phenomena developing in the runner and in the rotor-stator interaction, a time-frequency analysis is performed on the numeric pressure and torque signals. The combination between fluid-dynamic and time-frequency analysis makes it possible to identify and characterize three evolution phases: inception, growth and consolidation.

Numerical and Experimental Study on the Effect of Rotor–Stator Distance on Rotor–Stator Interaction Strength within Mixed-Flow Centrifugal Pumps

In this article, the influence of rotor–stator distance on the pump performance and rotor–stator interaction strength within mixed-flow centrifugal pump was investigated based on numerical calculation and test verification. Firstly, the performances of mixed-flow centrifugal pumps with two different rotor–stator distances were obtained and compared with the numerical results, which confirms the high accuracy of the numerical simulation. Next, the performances of mixed-flow centrifugal pumps with five different rotor–stator distances were compared and analyzed. It was found that the hydraulic performance of the mixed-flow centrifugal pump varies slightly as the rotor–stator distance increases. The mean values of the standard deviation of the head and efficiency of the mixed-flow centrifugal pump at each rotor–stator distance under full flow conditions are only 0.16 m and 0.11%, respectively. Then, the strengths of the rotor–stator interaction with different rotor–stator distances were analyzed. It was found that the strengths of the shock interaction, the wake interaction, and the potential interaction were all reduced with increasing rotor–stator distance. Moreover, when the rotor–stator distance is 1.5 mm, the pressure distribution in the circumferential direction of the rotor–stator interference zone shows obvious unstable characteristics: the pressure change amplitude is significantly greater than the other rotor–stator distance of the pressure change amplitude, the maximum and minimum pressure amplitude difference being 56.9 kPa, and with the increase in the rotor–stator distance, the maximum and minimum pressure amplitude difference gradually decreases, with an average value of 32.3 kPa. These findings could provide useful insight into prospects for the improvement of the operational stability of mixed-flow centrifugal pumps, and the results of this study can be extended to all centrifugal pumps using diffusers in the form of vanes as the pressure chamber, which has strong practical application and theoretical value.

Flow-induced noise sources and reduction methods in centrifugal pumps: A literature review

This Review describes the research work conducted by many researchers in the field of hydro-acoustics of centrifugal pumps. This study aims to understand the flow induced noise mechanism, factors affecting it, and available methods to attenuate the same in centrifugal pumps. In general, the noise generated by a pump is interpreted in terms of pressure pulsations and can be represented in the frequency domain as a combination of discrete components and broadband components. In the discrete frequency noise component, the major emphasis is given on blade pass frequency noise and its relation to the rotor–stator interaction in pumps. The intensified rotor–stator interaction results in high pressure pulsations, thus strong flow induced noise. The effect of various geometrical parameters on the rotor–stator interaction and available methods to mitigate it to reduce noise are discussed in detail. Apart from the rotor–stator interaction, the importance of energy loss mechanisms, such as flow recirculation, flow-separation, and jet-wakes occurrence in pumps, which affect the blade pass frequency component, are also discussed. One of the other discrete noise components, the rotating stall mechanism with its physical mechanism, was also explored in detail. Subsequently, two major phenomena of broadband noise components, turbulence and cavitation, are explained. For cavitation, the phenomenon is elaborated in detail as well as various methods explored by the researchers to predict the existence of the cavitation phenomenon using the acoustic spectrum. Conclusions are also drawn for each source by describing the major events. In the end, the possible future scope of work that can be explored is given.

Effect of the tip clearance on tip leakage vortex and pressure fluctuation characteristics in a helico-axial flow multiphase pump

Tip clearance inevitably exists in helico-axial flow multiphase pumps, which generates a great impact on flow characteristics. To select a reasonable tip clearance and improve the transporting efficiency, different tip clearances (Rtc = 0.5, 1.0, and 1.5 mm) are chosen to investigate the flow behaviors and hydraulic characteristics. Based on the shear stress transport k-ω turbulence model, the unsteady Reynolds averaged Navier–Stokes equations are applied to solve the unsteady flow. Results show that when the tip clearance increases, the tip leakage vortex (TLV) near the tip gradually becomes obvious and the pressure fluctuation near the TLV also becomes larger. The spatial–temporal evolution is divided into three stages: split stage, contraction stage, and recurrence stage. Besides, the rotor–stator interaction is still the primary cause for the pressure fluctuation.

Mechanism of the rotor−stator interaction in a centrifugal pump with guided vanes based on dynamic mode decomposition

In this paper, the mechanism of the rotor–stator interaction in a centrifugal pump with guide vanes is studied numerically and theoretically. The dynamic mode decomposition method is employed to decouple and reconstruct the unsteady flow. A diametrical mode theory suitable for centrifugal pumps with guided vanes is proposed to determine the source of harmonics with higher amplitudes quickly. The results show that the dominant frequencies of the pressure pulsation in the volute and guide vanes are the blade passing frequency and its harmonic frequencies, and the corresponding flow structure is stable and has higher modal energy. The rotor–stator interaction effect around the impeller outlet is most pronounced. The potential flow effect works on the impeller and guide vanes but decays rapidly. The pressure pulsation caused by the wake effect propagates downstream and persists for long distances, which is the main reason for forming the modal pressure field in the volute. The modal reconstruction can reproduce the dynamic evolution process of the pressure field at the characteristic frequencies. The propagation characteristics of the modal pressure field in the volute can be accurately predicted by theoretical analysis. This research can provide an essential reference for fault diagnosis and vibration control of the centrifugal pump.

Experimental and Numerical Investigation of Rotor–Stator Interaction in a Large Prototype Pump–Turbine in Turbine Mode

In recent years, large-capacity, high-head pump–turbine units have been developed for pumped storage power plants to effectively utilise water energy and store large amounts of electricity. Compared with the traditional Francis turbine unit, the radial distance between the trailing edge of the guide vanes and the leading edge of runner blades of high-head pump–turbine unit is smaller, so the rotor–stator interaction and the corresponding pressure fluctuations in the vaneless space of pumped storage units are more intense. The pressure fluctuations with high amplitudes and high frequencies induced by rotor–stator interaction (RSI) become the main hydraulic excitation source for the structures of the unit and may cause violent vibration and fatigue damage to structural components, and seriously affect the safe operation of the units. In this paper, the RSI of a high-head pump–turbine in turbine mode of operation is studied in detail by means of site measurement and full three-dimensional unsteady simulations. The results of RSI-induced pressure fluctuations in turbine mode are analysed experimentally and numerically. The accuracy of the numerical calculations is verified by comparing with the measured results, and the variation law of RSI is deeply analysed. The results show that the pressure fluctuations in the vaneless space are affected by the wake of the guide vane, the rotating excitation of the runner, the low-frequency excitation of the draft tube, and the asymmetric characteristics of the incoming flow of the spiral case, and shows significant differences in spatial position. The findings of the investigation are an important and valuable reference for the design and safe operation of the pumped storage power station. It is recommended to design the runner with inclined inlets to reduce the amplitudes of RSI-induced pressure fluctuations and to avoid operating the pump–turbine units under partial load for long periods of time to reduce the risk of pressure fluctuation induced severe vibration on the structures.

Acoustic pre-design studies of ducted fans for small aircraft

This publication presents an analytical method for the aerodynamic and acoustic pre-design of ducted fans for small aircraft. Based on studies of the primary design variables, the paper discusses the physical sound generation phenomena, as well as the interdisciplinary relationships of ducted fan design. First, the fan design and analysis methods are described. On the basis of an aerodynamic mean line method, the radial distribution of the flow velocities is used to determine the steady blade flow. Unsteady aerodynamic excitations are calculated by means of Sears’ blade response function. To determine the generation and propagation of sound within the ducted fan, Goldstein’s acoustic analogy is solved analytically. The methods are applied to a reference case, for which studies show that ducted fans offer significant potential in reducing sound emission, compared to free propellers. Since the rotor-alone noise of subsonic ducted fans is always cut-off, tonal sound is predominantly excited by rotor–stator interactions. These sources can be significantly reduced by a proper selection of the rotor blade and stator vane numbers, as well as optimal lean and sweep of the stator vanes. Large diameters and axial gaps are acoustically advantageous, but reduce fan stage efficiency and increase nacelle drag due to large wetted areas, especially at cruise. As a result, the importance of considering these complex interdependencies in a comprehensive design approach is shown. The pre-design method presented can be used to determine an optimal ducted fan design, taking into account interdisciplinary trade-offs, with an emphasis on noise. Analysis of the ducted fan concept shows that the ducted fan can be a promising alternative to the free propeller, especially if low noise emission is required.

Investigation on the Effect of the Shaft Transition Form on the Inflow Pattern and Hydrodynamic Characteristics of the Pre-Shaft Tubular Pump Device

The shaft tubular pump device is widely used in low head pumping stations in plain areas. The N-S equation and the SST k-ω turbulence model are adopted. Then, the investigation on the influence of the shaft transition form on the inflow pattern and hydrodynamic characteristics of the pre-shaft tubular pump device is carried out. By designing three transition forms of shafts, different inflow patterns are provided for the tubular pump device. The characteristic parameters of the shafts and external and internal flow characteristics of the pumping device under different inflow patterns are compared and analyzed. Finally, the optimal transition form is selected for model tests, and unsteady pressure pulsation characteristics are studied. The results show that the flow pattern in the inlet passage of each case is relatively uniform and smooth, and the range of the high-efficiency zone of the pump device is roughly within 0.9Qd–1.2Qd. The energy loss and the weighted average angle on the outlet of each case are similar. The axial velocity distribution uniformity on the impeller inlet of case 1 is better than that of the other cases. The numerical simulation results are consistent with the experimental results, and the numerical simulation method is reliable. Under the design condition, the pressure pulsation amplitude at the impeller inlet is the largest. It gradually increases from the hub to the shroud. The main frequency of pressure pulsation is the blade frequency. The pressure pulsation amplitude at the impeller outlet decreases from the hub to the shroud. The main frequency is not constant due to the rotor–stator interaction between the impeller and the guide vane. The outcome will be beneficial to the design and optimization of the shaft tubular pump device, which is helpful for broadening the corresponding theory and applying it to the actual project.

Zonal Detached Eddy Simulation of the Fan-Outlet Guide Vanes Stage of a Turbofan Engine: Part II—Broadband Noise Predictions

Abstract This paper (Part II) presents the broadband noise predictions of a turbofan stage based on a hybrid method proposed by ONERA in the framework of the European project TurboNoiseBB. The numerical approach relies on a ZDES (Zonal Detached Eddy Simulation) strategy that is applied to a fan module at approach conditions and tested in AneCom facility (Wildau, Germany). The ZDES method with main aerodynamic flow features is detailed in a companion paper (Part I), and this one focuses on acoustic analyses. Acoustic codes based on Amiet's theory and FWH (Ffowcs Williams and Hawkings) analogy, both taking into account for duct propagation effects, are briefly described in the article and chained to the computational fluid dynamics to assess the rotor–stator interaction (RSI) noise (focusing on stator sources). The required inputs are the turbulent wake information (issued from either Reynolds Averaged Navier-Stokes (RANS) or ZDES) in front of the stator and the unsteady pressure on the vane wall, respectively. Turbulent velocity profiles and velocity spectra are compared to hot-wire measurements in the interstage region. A nice agreement is globally observed with a clear improvement compared to RANS solutions. Then, sound power spectra in the intake and bypass duct provided by acoustic codes are discussed and compared to the experiment. Reliable numerical predictions are obtained when undesirable additional sources in the rear-chord region (believed to be caused by local flow detachments from the vane leading edge and near the trailing edge) are removed from the FWH surface integration. ZDES + FWH spectra are found to be not so far from RANS + Amiet ones, with a best fitting to the experimental spectrum shape and predicted levels 3 dB below the measurements.

Zonal Detached Eddy Simulation of the Fan-Outlet Guide Vanes Stage of a Turbofan Engine: Part I—Methodology, Numerical Setup, and Aerodynamic Analysis

Abstract This article deals with the zonal detached eddy simulation of the fan module of a modern turbofan engine for the prediction of the broadband noise due to the interaction of the fan turbulent wakes with the stationary outlet guide vanes. The simulation relies on a hybrid RANS/LES approach with a zonal strategy: the core airflow is treated in RANS, while the bypass airflow is solved with the hybrid approach. The simulation was performed during four revolutions, and statistical convergence was reached. Inspections of the flowfields highlight a consistent behavior of the shielding function (border between RANS and LES solving areas) around the blade walls and at the trailing edge for a such complex flow. The fan module was tested in the AneCom facility in which hot wire measurements were made in-between the fan and the outlet guide vanes. The numerical results are compared to this large dataset of measurements. The flow maps are well retrieved by the simulation for both the time-averaged and the turbulent quantities. Comparison of radial profiles shows an excellent agreement for the three root-mean-square (RMS) components of the velocities between zonal detached eddy simulation (ZDES) and the measurements, particularly in the tip gap flow area, in which RANS results do not reproduce correctly the flow quantities. The wake shape, a key feature in the mechanism of generation of rotor–stator interaction noise), is quite well predicted by the ZDES simulation. These numerical results demonstrate the maturity of the approach for the simulation of complex turbomachinery flows.

Numerical Evaluation in a Scaled Rotor-Less Nozzle Vaned Radial Turbine Model under Variable Geometry Conditions

The widespread trend of pursuing higher efficiencies in radial turbochargers led to the prompting of this work. A 3D-printed model of the static parts of a radial variable geometry turbine, the vaned nozzle, and the volute, was developed. This model was up-scaled from the actual reference turbine to place sensors and characterize the flow around the nozzle vanes, including the tip gap. In this study, a computational model of the scaled-up turbine was carried out to verify the results in two ways. For this model, firstly compared with an already validated CFD turbine model of the real device (which includes a rotor), its operating range was extended to different nozzle positions, and we checked the issues with rotor–stator interactions as well as the influence of elements such as the screws of the turbine stator. After showing results for different nozzle openings, another purpose of the study was to check the effect of varying the clearance over the tip of the stator vanes on the tip leakage flow since the 3D-printed model has variable gap height configurations.