Closed-loop Test Rig Research Articles

Vortex-induced energy loss and pressure fluctuations in a closed sump under various conditions: An experimental investigation

The roof-attached vortices (RAVs), floor-attached vortices (FAVs), and complex combined submerged vortices (CSVs) excited in a closed pump sump will induce irregular pressure fluctuations that can decrease the energy efficiency of the pump and the stability of its input flow. This article presents an experimental investigation of the energy loss and pressure fluctuations induced by these vortices under various conditions. A transparent closed-loop test rig was used for high-speed visualization and pressure-fluctuation tests. The findings demonstrate that as the flow rate is increased, the head and efficiency of the pump device significantly decrease. A CSV, which is composed of an RAV and an FAV, has the highest head-loss value, reaching 0.21 m, with an efficiency decrease in up to 2.8%. The typical evolution stages of RAV are divided into newborn, developing, fully developed, and dissipative collapsing. The typical evolution stages of FAV are divided into germinating, growing, maintaining, decaying, and disappearance. The maximum diameter of the FAV core is approximately 0.05 times the maximum vortex-core scale of the RAV. Based on the proposed vortex-identification method, as the bellmouth height decreases, the strength of the FAV increases during the CSV period, and the degree of pressure fluctuation becomes more severe. In addition, regardless of the flow rate, the strength of the FAV structure is always much greater than that of the RAV.

Spatial-temporal evolution and pressure fluctuation characteristics of the combined submerged vortex in a closed pump sump

Following the retrofit of the pump sump, there is a high risk of inducing the Combined Submerged Vortex (CSV), which consists of the roof-attached vortex (RAV) and floor-attached vortex (FAV). This vortex formation can lead to irregular pressure fluctuations, adversely affecting the unit's performance and compromising the stability of energy conversion. This study aims to investigate the spatiotemporal evolution of the CSV and its associated pressure fluctuation characteristics in a closed pump sump. High-speed visualization and pressure fluctuation tests are conducted on a transparent closed-loop test rig. The findings demonstrate that the spatiotemporal evolution of the CSV can be divided into three stages: developing, competing, and collapsing. The competing stage, in particular, has a significant impact on the FAV. During the CSV period, the dominant low frequencies induced by the RAV and FAV are 0.24 and 0.13 Hz, respectively, with the FAV exhibiting higher intensity than the RAV. The regions of high coherence between the RAV and FAV are primarily concentrated within the low-frequency range of 0.25–2 Hz, and the signals exhibit multiple phase differences. Furthermore, a vortex identification criterion for a closed sump is proposed based on Continuous Wavelet Transform.

Effect of clocking on entropy noise generation within an aeronautical high pressure turbine stage

This article reports a detailed experimental and numerical study of the clocking effect between entropy wave spots and stator leading edges on the evolution of the entropy wave and on indirect noise generation in a high pressure turbine stage. Experimental campaigns considering burner-representative temperature fluctuations injected upstream of an uncooled high-pressure gas turbine stage have been performed in the high-speed closed-loop test rig of the Fluid Machine Laboratory (LFM) of the Politecnico di Milano. Acoustic measurements focused on entropy noise generation have been carried out by the German Aerospace Center, DLR with two flush mounted in-duct microphone arrays. URANS CFD simulations with and without entropy fluctuations imposed at the stage inlet were performed with the TRAF code, developed by the Università degli Studi di Firenze. A numerical post-processing procedure, based on the time and space discrete Fourier transform (DFT) of the conservative variables, has been implemented to extract the low-frequency content connected to the entropy fluctuations and indirect noise emissions. Simulations show an overall good agreement with the experiments, especially at the stage outlet thus confirming the possibility to predict entropy noise by means of URANS simulations with time varying inlet conditions. By exploiting the combination of experiments and simulations, the evolution of the entropy wave, the identification of entropy noise generation areas, and the evaluation of indirect noise emissions, for the different clocking positions were properly assessed. This study also demonstrates that this type of simulations can be used for the geometric design optimization of combustor/turbine coupling performing detailed parametric studies concerning the clocking position of the perturbation source in order to reduce the turbine-combustor interactions and the indirect noise emissions.

Aerodynamic simulation of a high-pressure compressor stage using the lattice Boltzmann method

PurposeThe present paper aims at evaluating the lattice Boltzmann method (LBM) on a high-subsonic high-pressure compressor stage at nominal regime.Design/methodology/approachThe studied configuration corresponds to the H25 compressor operated in a closed-loop test rig at the von Karman Institute. Several operating points are simulated with LBM for two grids of successive refinements. A detailed analysis is performed on the time-averaged flow predicted by LBM, using a comparison with experimental and existing RANS data.FindingsThe finest grid is found to correctly predict the mean flow across the machine, as well as the influence of the rotor tip gap size. Going beyond time-averaged data, some flow analysis is performed to show the relevance of such a high-fidelity method applied to a compressor configuration. In particular, vortical structures and their evolution with the operating points are clearly highlighted. Spectral analyses finally hint at a proper prediction of tonal and broadband contents by LBM.Originality/valueThe application of LBM to high-speed turbomachinery flows is very recent. This paper validates one of the first LBM simulations of a high-subsonic high-pressure compressor stage.

Computational and Experimental Study of the Unsteady Convection of Entropy Waves Within a High-Pressure Turbine Stage

Abstract This article describes the transport and the interaction of pulsating entropy waves generated by combustor burners within a high-pressure turbine stage for aeronautical application. Experiments and computational fluid dynamics (CFD) simulations were carried out in the context of the European Research Project RECORD. Experimental campaigns considering burner-representative temperature fluctuations (in terms of spot shape, fluctuation frequency, and total temperature variation percentage) injected upstream of an un-cooled high-pressure gas turbine stage have been performed in the high-speed closed-loop test rig of the Fluid Machine Laboratory (LFM) of the Politecnico di Milano (Italy). The pulsating entropy waves are injected at the stage inlet in streamwise direction at four different azimuthal positions featuring a 7% overtemperature with respect to the main flow with a frequency of 90 Hz. Detailed time-resolved temperature measurements (in the range of 0–200 Hz) upstream and downstream of the stage, as well as in the stator–rotor axial gap, were performed. Time-accurate CFD simulations with and without entropy fluctuations imposed at the stage inlet were performed with the TRAF code, developed by the Università degli Studi di Firenze (Italy). A numerical postprocessing procedure, based on the discrete Fourier transform (DFT) of the conservative variables, has been implemented to extract the low-frequency content connected to the entropy fluctuations. Measurements highlighted a significant attenuation of the entropy wave spot throughout their transport within the stator channel and their interaction with the rotor blade rows, highly depending on their injection azimuthal position. Simulations show an overall good agreement with the experiments on the measurement traverses, especially at the stage outlet. By exploiting the combination of experiments and simulations, the aerodynamic and thermal implications of the temperature fluctuation injected upstream of the stage were properly assessed, thus allowing suggest useful information to the designer. The comparison with the experiments confirms the accuracy of the CFD method to solve the periodic, but characterized by a low-frequency content event, associated with the entropy wave fluctuation.

Measurements of Fast Transitions at a Reversible Pump Turbine Model in Closed Loop Test Rig

It is common practice to experimentally investigate the performance characteristics of hydraulic fluid machinery in power plants with steady-state operating points by scaled homologous model machines in closed-loop test rigs. In this case, the piping of the main water conduit from the power plant and the test rig plays a minor role. However, for studies of operating transient, e.g. load rejection, the influence of the weak compressibility of water in the pipes is considered by 1-D water hammer analyses. Due to differences in the main water conduit between the power plant and the test rig, the test rig is specifically controlled by new procedures to replicate the relevant conditions at the fluid machine in the test rig under similarity conditions.The results of this newly developed method for specific control of the test rig for operating transients are presented and successfully validated on a closed-loop experimental system. In future, suitable instrumented model machines then allow the measurement of dynamic pressures or even strains in and on machine components in order to elaborate, as a goal, the influence of different operating transients on the service life of machine components. Furthermore, these experimental data can also be used to validate Computational Fluid Dynamics (CFD) and Finite Element Analyses (FEA) simulations.

Computational and Experimental Study of Hot Streak Transport Within the First Stage of a Gas Turbine

Abstract The paper discusses the migration, the interaction with the blades, and the attenuation of hot streaks generated by combustor burners, during their propagation within the first turbine stage of aero-engines. Experiments and computational fluid dynamics (CFD) simulations were carried out in the framework of the European Project RECORD and on its follow-up. Measurements considering burner-representative temperature perturbations injected upstream of an un-cooled high-pressure gas turbine stage were performed in the high-speed closed-loop test-rig of the Politecnico di Milano (Italy). The hot streaks were injected in a streamwise direction at the stage inlet in four different circumferential positions with respect to the stator blade. They feature a 20% over-temperature with respect to the main flow. Detailed temperature measurements as well as unsteady aerodynamic measurements upstream and downstream of the blade rows were performed. Time-accurate CFD simulations of the flow upstream and within the turbine stage were performed with the TRAF code, developed by the Università degli Studi di Firenze (Italy). Measurements show a relevant attenuation of hot streaks throughout their transport within the stator and the rotor blade rows, highly depending on the injection azimuthal position. The perturbations were observed to lose their spatial coherence, especially in the transport within the rotor, and to undergo severe spanwise migration. Simulations exhibit a good agreement with the experiments on the measurement planes and allow tracking the complex flow phenomena occurring within the blade rows. Finally, the aerodynamic and thermal implications of the inlet temperature perturbations are properly highlighted and discussed.

Data-Driven Model-Free Control of Torque-Applying System for a Mechanically Closed-Loop Test Rig Using Neural Networks

This paper presents a data-driven approach that utilizes the gathered experimental data to model and control a test rig constructed for the high-powered gearboxes. For simulating a wide variety of operational conditions, the test rig should be capable of providing different speeds and torques; this is possible using a torque-applying system. For this purpose, Electro-Hydraulic Actuators (EHAs) are used. Since applying accurate torque is a crucial demand as it affects the performance evaluation of the gearboxes, precise modelling of the actuation system along with a high-performance controller are required. In order to eliminate the need to solve complex nonlinear equations of EHA that originate from friction, varying properties of flow and similar, a data-driven system based on neural networks is used for modelling. In this manner, the model of the system, which captures the whole dynamic of the system, can be obtained without any simplifying assumptions. The model is validated with experimental data, and the learning factors are set to zero to reduce the high computational costs. After that, another network of neurons is used as a controller. The performance of the proposed controller under normal conditions and in the presence of disturbances are investigated. The results show a good tracking of this controller for various reference inputs in different conditions with acceptable characteristics. Additionally, the obtained results are compared with a conventional proportional-integral-derivative (PID) controller results, and the superior features of the proposed scheme is concluded.

Method to Transfer Transient Prototype Conditions to Closed-Loop Model Test Rig

This paper describes a method for determining the sequence of transient model test experiments in a closed loop testrig, using previous 1D-simulations. An existent power plant with reversible pump turbine in the Austrian Alps serves as baseline. First, real measurement data of power jumps are reproduced in 1D-simulations. These simulation results were transferred to the scaled model size via similarity laws. Of particular importance is the choice of model to prototype speed ratio whose influence has been studied more closely. Subsequently, the transient processes are simulated in a closed loop test-rig. The simulations are controlled by a temporal power variation of the service pump. An iteration loop with optimizer has adapted the power in order to achieve similar conditions as in the prototype simulation. Due to the good reproducibility of the power jumps in the closed loop model test-rig more demanding processes are investigated in the next step. A fast transition with load rejection and guide vane closing has been simulated, as it is state of the art. Furthermore, it was assumed that this power plant also has a full size frequency converter for fast transition from pump mode to turbine mode and vice versa applying linear speed variation. The findings of the pump behavior as well as the test-rig behavior can then be used for the transient model test experiments.

Dynamic analysis of a helical gear reduction by experimental and numerical methods

Presented in this study is investigation of dynamic behavior of a helical gear reduction by experimental and numerical methods. A closed-loop test rig is designed to measure vibrations of the example system, and the basic principle as well as relevant signal processing method is introduced. A hybrid user-defined element model is established to predict relative vibration acceleration at the gear mesh in a direction normal to contact surfaces. The other two numerical models are also constructed by lumped mass method and contact FEM to compare with the previous model in terms of dynamic responses of the system. First, the experiment data demonstrate that the loaded transmission error calculated by LTCA method is generally acceptable and that the assumption ignoring the tooth backlash is valid under the conditions of large loads. Second, under the common operating conditions, the system vibrations obtained by the experimental and numerical methods primarily occur at the first fourth-order meshing frequencies and that the maximum vibration amplitude, for each method, appears on the fourth-order meshing frequency. Moreover, root-mean-square (RMS) value of the acceleration increases with the increasing loads. Finally, according to the comparison of the simulation results, the variation tendencies of the RMS value along with input rotational speed agree well and that the frequencies where the resonances occur keep coincident generally. With summaries of merit and demerit, application of each numerical method is suggested for dynamic analysis of cylindrical gear system, which aids designers for desirable dynamic behavior of the system and better solutions to engineering problems.

Analysis of a high-pressure screw compressor performances

Oil flooded screw compressors with discharge pressures of up to 26 bar have been available, commercially for some years. However, demands for higher pressure operation led to the design, construction and testing of a compressor operating with discharge pressures of up to 45 bar. To maximize the compressor efficiency, extensive performance simulations were carried out. Since 1980 oil flooded screw compressors have been used in many process gas compression applications and in the last year the higher pressure and larger capacity was realized. From 2010 to 2015 INCDT COMOTI manufactured screw compressors under GHH-Rand license (CU type, with max. delivery pressure 26 bar). Experience gain in this process gives us the power to develop the new type of screw compressors - based on license - with high delivery pressure - max. 45 bar. This paper will present details about the tests with a new high pressure screw compressor test in a closed loop test configuration. The machine was then tested in a closed loop test rig and, as is shown, the measured performance agrees well with that predicted by the numerical model. The parameters will be analysed starting from CFD modelling of the process and finally comparative analysis with actual parameters. The demonstrated advantages of this type of compressor, like high reliability, simple foundations, low operational cost, low initial cost, suitability for process fluctuation - gas pressure, gas composition - led to a significant demand for such compressors.

Transfer of transient conditions from prototype to closed-loop model test rig

This paper describes a method for determining the sequence of transient model test experiments in a closed loop test-rig, using previous 1D-simulations. A real power plant with reversible pump turbine in the Austrian Alps serves as baseline. A fast transition with load rejection and guide vane closing has been simulated, as it is state of the art. Furthermore, it was assumed that this power plant also has a full size frequency converter for fast transition from pump mode to turbine mode and vice versa applying linear speed variation. These simulation results were transferred to the scaled model size via similarity laws. Of particular importance is the choice of model to prototype speed ratio whose influence has been studied more closely. Subsequently, the transient processes are simulated in a closed loop test-rig. The simulations are controlled by a temporal power variation of the service pump. An iteration loop with optimizer has adapted the power in order to achieve similar conditions as in the prototype simulation. The findings of the pump behavior can then be used for the transient model test experiments.

An improved model for dynamic analysis of a double-helical gear reduction unit by hybrid user-defined elements: Experimental and numerical validation

This paper introduces an improved model generated by hybrid user-defined element method (HUELM) for dynamic analysis of a double-helical gear reduction unit. Based on theories of structural dynamics and system dynamics, the model consists of four developed elements to respectively simulate the gear pair, bearings, flexible shafts and the housing. A closed-loop test rig is constructed to validate the model: an encoder-based method is applied to measure vibration acceleration of the gear pair, and accelerometer-based measurement systems are employed to obtain the dynamic responses of the housing. Furthermore, two additional models by the finite element method (FEM) and the lumped mass method (LMM) are constructed for numerical comparison to illustrate the HUELM's substantial advantages. Compared with the LMM, the HUELM is of capacity to investigate the interaction among the subsystems; moreover, it is more efficient than the FEM primarily because of the integrated tooth contact analysis method and loaded tooth contact analysis method. It is demonstrated that the predictions by the HUELM match well with the experimental data in terms of meshing frequencies and vibration responses. It is also concluded from the numerical comparison that the HUELM is appropriate for dynamic analysis, particularly of large complex transmission equipment.

Design of a mechanically closed-loop test rig for testing aviation industry’s gearboxes

Due to the wide usage of rotary equipment and the necessity of their testing for maintenance and repair, test rigs have become necessary. The mechanical closed-loop test rig developed in Sharif University of Technology branch of ACECR (Academic Centre of Education, Culture and Research) is a test rig with low energy losses that is suitable for testing high power gearboxes such as aerospace or wind turbine gearboxes. It can be loaded up to 489Hp at a maximum speed of 3000 rpm, and the test components can be tested in different testing conditions including a variety of torques and speeds. This paper describes the preliminary, conceptual, and detailed design, steps including frame work design, control system design, hydraulic system and torque generator design asn well as a dynamic and static analysis of the whole system. Also a simplified model of the system is presented and qualified, and some data of test rig’s working conditions is presented. These data includes the temperature change of the gearboxes, their vibration in time, and also the variation of torque, hydraulic pressure, and motor speed. Furthermore, the relation between these parameters is investigated to determine the behaviour of the system. The validity of the system’s dynamic modelling is also investigated and verified.

Experimental investigation and performance prediction modeling of a single stage centrifugal pump operating as turbine

In small hydropower systems, Pumps as Turbines (PaTs) represent a cost-effective alternative to conventional turbines as long as the turbine mode performance can be predicted before their installation. A closed-loop test rig for experimental studies on hydraulic pumps and turbines has been built at the Department of Mechanics, Mathematics and Management of the Polytechnic University of Bari, in order to experimentally support the theoretical studies on PaTs. A single stage centrifugal pump has been tested in both direct and reverse mode. Furthermore, a literature survey of PaT models has been conducted and a new model, with a more general applicability, has been proposed.

Realtime-capable FE-based railway catenary emulation via pantograph test rig impedance control

This work shows novel results of emulating railway catenary dynamics on a test rig for pantograph testing in order to provide for virtual test rides of railway pantograph current collectors under laboratory conditions. A realtime-capable finite-element model of a railway catenary is formulated efficiently in moving coordinates. An advanced test rig impedance control architecture is adopted for the finite-element model structure, and detailed simulations of an existing full-size pantograph test rig are carried out. The high fidelity of the realtime catenary model as well as the emulation performance of the closed-loop test rig setup in contact with a pantograph model provides promising results for the future implementation of the simulation/control architecture on the test rig hardware.

Experimental study on thermal performance of optimum PG brine as a radiator coolant

AbstractThe present study deals with the experimental impact of an alternative heat transfer fluids for overall performance improvement for radiators. Water and water mixed with anti‐freezing agents such as ethylene glycol (EG) and propylene glycol (PG) are the traditional coolants for an automotive radiator. Comparison of experimental and numerical analysis of optimum brine solution, that is 25% of propylene glycol and water as coolant for the rectangular fin radiator, has been well discussed. A closed loop test rig was designed, and fabricated with a wind tunnel section to achieve uniform velocity at the test section of the rectangular radiator and was tested for performance. Experimental runs were conducted at varying operating temperatures which included the runs for water, and an optimum propylene glycol brine solutions at 70 °C and 80 °C with various flow rates. Results show the energy performance of an optimum brine solution was nearly similar to that of water at high temperatures. The Nusselt number, heat transfer coefficient, and heat transfer rate for an optimum propylene glycol brine is nearly the same as water at 80 °C with a maximum deviation of 15%, 5.7%, and 6.6%, respectively, for theoretical and experimental result comparisons. Air side and coolant side pressure drops had a maximum deviation of 3.66% and 6.6%, respectively. Air and coolant exit temperatures had a deviation of 5% and 3.5%, respectively, with an air frontal velocity of 4.6 m/s in a rectangular fin radiator for an optimum brine solution used as coolant for the automotive radiator. The optimum propylene glycol brine may be environmentally beneficial.

Fractional Order PID Control mechanism for Helicopter Gearbox Test Control with internal and External Disturbance

Fractional order PID (FOPID) controller is a special kind of PID controller which it’s derivative and integral order are fractional rather than integer and has five parameters. Using this control improves the control results in accuracy and speed. Statistics show that using this controller for systems with high sensitivity is more practical and safe. Mechanical closed loop test rig acts an important role in aviation industry. Fault diagnosis in gearboxes and other critical components of the airplane and helicopters is the most important part of this industry. More over testing rotating equipment is very important for system security verification. There are several testing technics and many important testing parameters. One of these essential factors is gearbox security test technique. What’s more, mechanical closed-loop system is a very cost effective method. For financial, energy consumption and maintenance reasons, using a system with the ability of energy regeneration is suggested. In this paper mechanical close loop with energy regeneration mechanism is used for testing the helicopter gearbox. Two kinds of controllers are used for keeping the closed-loop’s torque in the constant value. The result of paper shows the behavior of PID and FOPID controller methods in controlling torque circulating in this mechanical closed loop. Beside the overshoot and settling time is considerable.

Prefiltration/Clarification via Dynamic Particle Separation

The project seeks to develop a non-fouling medialess inertial particle separator for use in industrial wastewater applications. The device, capable of removing fine particles from a fluid upstream of a media filter, will significantly reduce particle loading, thereby increasing its service life. The self-cleaning particle separator uses boundary layers on rotating disks to dynamically separate entrained particles suspended in fluids. The research specifically addresses potential improvements in the operation of industrial wastewater treatment facilities by enhancing efficiency, reliability and longevity of conventional filtration media. Fabrication of a closed-loop test rig will allow the operational envelope of a prototype prefilter challenged by ISO fine test sand and colloidal (Latex) microspheres to be parametrically assessed, establishing the influence of operational parameters on particle separation efficiency and pressure differential. Quantitative analyses of the effluent will generate particle size distributions, as well as turbidity reduction measurements. The project will advance the understanding of this separator technology in liquids. This title belongs to WERF Research Report Series ISBN: 9781843396703 (eBook)

Real Time Closed-loop Test Rig for Decentralized Control of Smart Distribution Networks

Electric power grids are moving towards Smart Grids and many new energy sources and loads are being integrated into distribution networks requiring the network to become more active and smart. The distribution networks have not been designed to cope with new constraints set up by the new energy sources and complex loads and will result in a number of adverse impacts. There is a considerable need for developing new algorithmic solutions for decentralised control within distribution networks and validating them at laboratory level before they can be successfully applied in the power grid. This research work addresses the development of a real time test rig which provides a decentralised control environment in distribution networks, onto which data management and network control functions are able to be implemented in a closed loop fashion, to observe their performance. This work also describes the development of a substation network controller; a platform that provides a closed loop test system for research, development, testing and validation of real time distribution network management and control functions.