Understanding the Dynamics of Critical Transitions in a Contra-Rotating Fan

2021 ◽  
Author(s):  
Manas Madasseri Payyappalli ◽  
A. M. Pradeep
Keyword(s):  
Mass Flow ◽  
Unstable Mode ◽  
Low Frequencies ◽  
Flow Rates ◽  
High Frequencies ◽  
Tip Leakage ◽  
Critical Transitions ◽  
Mode Of Operation ◽  
Mass Flow Rates ◽  
Low Mass

Abstract In this experimental study, we investigate the fundamental behaviour of a low speed contra-rotating fan and describes the reasons leading to the instabilities in the fan at low mass flow rates. A contra-rotating fan is a possible alternative to conventional fans and has potential aerodynamic advantages. This study identifies certain features that are unique to a contra-rotating configuration. Rotor-1 and rotor-2 behaves differently at low mass flow rates. Though rotor-1 is stable up to low mass flow rates, rotor-2 enters into an unstable mode of operation at mass flow rates close to the design mass flow rate. The critical region where the instability arise in rotor-1 is its tip and in rotor-2 is its hub. The instability is also found to change the structure as it propagates along the annulus. It is identified that the presence of rotor-2 downstream of rotor-1 under-loads rotor-1 and thus significantly affects the loading on rotor-1. The instability arises due to the tip-leakage vortex at high frequencies and due to modal waves at low frequencies. The study thus identifies the major regions of the rotors which are the sources of instabilities and also identifies the process of transition to instability in the contra-rotating fan.

scholarly journals Simulation and Modeling of Flow in a Gas Compressor

2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Anna Avramenko ◽  
Alexey Frolov ◽  
Jari Hämäläinen
Keyword(s):  
Steady State ◽  
Mass Flow ◽  
Gas Flow ◽  
Simulation Method ◽  
High Mass ◽  
Ansys Fluent ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Low Mass ◽  
Flow Through

The presented research demonstrates the results of a series of numerical simulations of gas flow through a single-stage centrifugal compressor with a vaneless diffuser. Numerical results were validated with experiments consisting of eight regimes with different mass flow rates. The steady-state and unsteady simulations were done in ANSYS FLUENT 13.0 and NUMECA FINE/TURBO 8.9.1 for one-period geometry due to periodicity of the problem. First-order discretization is insufficient due to strong dissipation effects. Results obtained with second-order discretization agree with the experiments for the steady-state case in the region of high mass flow rates. In the area of low mass flow rates, nonstationary effects significantly influence the flow leading stationary model to poor prediction. Therefore, the unsteady simulations were performed in the region of low mass flow rates. Results of calculation were compared with experimental data. The numerical simulation method in this paper can be used to predict compressor performance.

Analysis of the Mixing Plane Interface Between Stator and Rotor of a Transonic Axial Turbine Stage

2000 ◽  
Author(s):  
P. Giangiacomo ◽  
V. Michelassi ◽  
F. Martelli
Keyword(s):  
Mass Flow ◽  
Static Pressure ◽  
Three Dimensional ◽  
Turbine Stage ◽  
Flow Rates ◽  
Tip Leakage ◽  
Mass Flow Rates ◽  
Stator Blade ◽  
Transonic Turbine ◽  
Rotor Mass

A three-dimensional transonic turbine stage is computed by means of a numerical simulation tool. The simulation accounts for the coolant ejection from the stator blade and for the tip leakage of the rotor blade. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The analysis is focused on the matching of the stator and rotor mass flow rates. The computations proved that the mixing plane approach allows the stator and rotor mass flow rates to be balanced with a careful choice of the stator-rotor static pressure interface. At the same time, the pitch averaged distribution of the transported quantities at the interface for the stator and rotor may differ slightly, together with the value of the static pressure at the hub.

EFFERVESCENT ATOMIZATION AT LOW MASS FLOW RATES. PART I: THE INFLUENCE OF SURFACE TENSION

1993 ◽  
Vol 3 (1) ◽  
pp. 77-89 ◽  
Author(s):  
M. T. Lund ◽  
Paul E. Sojka ◽  
Arthur H. Lefebvre ◽  
P. G. Gosselin
Keyword(s):  
Surface Tension ◽  
Mass Flow ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Low Mass

Design and Development of a Radial Turbine for Low Flow Turbocharging

2019 ◽  
Author(s):  
Dhinagaran Ramachandran ◽  
Srinivasa Rao Billa ◽  
Balamurugan Mayandi ◽  
Perumal Balappan ◽  
Shyamaprasad Kanthila ◽  
...  
Keyword(s):  
Transient Response ◽  
Mass Flow ◽  
Aerodynamic Performance ◽  
Low Flow ◽  
Angle Distribution ◽  
Turbine Wheel ◽  
Structural Requirements ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Low Mass

Abstract The scope of this study is to develop a turbocharger turbine wheel with improved aerodynamic performance at low mass flow rates and with reduced inertia for better transient response. The contrasting effect of geometrical shape and size parameters on the objectives of aerodynamic performance and transient response gives rise to the need to explore the design space for the best design having good trade-off between the multi-objective requirements. The search for an optimum aerodynamic design is a challenge due to structural requirements as well. A turbine wheel that is best suited for the current application is selected from the library as a baseline and this wheel is further optimized to meet the targets. Preliminary screening allowed the identification of parameters having major impact on the objectives and these results have been used to train a Response Surface (RS). Further, in the interest of reducing computational cost, a virtual optimization algorithm based on the RS has been employed to predict optimum design within the design constraints. The optimum designs thus obtained are validated with Computational Fluid Dynamics simulations for flow performance and Finite Element solver for satisfying structural requirements. This approach has allowed for application-based design of turbine wheel for instance, by changing key parameters like blade angle distribution, number of blades, axial length, blade height and width. An inertia reduction up to 10% has been obtained while retaining the performance at low mass flow rates.

Heat removal from VVÉR fuel assemblies for low mass flow rates

1990 ◽  
Vol 68 (4) ◽  
pp. 337-341
Author(s):  
B. G. Gordon ◽  
V. N. Pomel'nikov
Keyword(s):  
Mass Flow ◽  
Heat Removal ◽  
Flow Rates ◽  
Vver Fuel ◽  
Fuel Assemblies ◽  
Mass Flow Rates ◽  
Low Mass

An Integrated Design Approach for Turbocharger Turbines Based on the Performance Optimization in Transitory Conditions

2018 ◽  
Author(s):  
Matteo Checcucci ◽  
Michele Becciani ◽  
Juri Bellucci ◽  
Alessandro Bianchini ◽  
Giovanni Ferrara ◽  
...  
Keyword(s):  
Mass Flow ◽  
High Performance ◽  
Maximum Efficiency ◽  
Time Lags ◽  
Acceleration Phase ◽  
Good Efficiency ◽  
Flow Rates ◽  
Design Point ◽  
Mass Flow Rates ◽  
Low Mass

Turbocharged engines are setting themselves as the present standard in case of high-performance engines for sport applications. The coupling of a turbomachine with an internal combustion engine poses, however, some serious challenges, especially regarding the time lags and the transitory flow conditions. In particular, focus is presently being paid to the acceleration phase of these sport vehicles, where the mass flow is much lower than that attended at maximum efficiency condition and the transitory response of the turbocharger becomes pivotal to provide promptly high compression ratios to the engine. In this view, the global optimization process of new turbochargers must be oriented not only at maximizing the aerodynamic efficiency at the best design point but also at providing good efficiency at low mass flow rates, combined with a reduced inertia to enable fast acceleration. In the study, a multi-objective methodological approach is presented aimed at designing the turbine of a high-performance turbocharged engine based on the following requirements: 1) high efficiency at the design point; 2) good efficiency at low mass flow rates, typical of the acceleration phase; 3) reduced inertia; 4) overall aerodynamic design adaptable with constructive constraints. In doing so, some design considerations are also provided, pointing out the different design choices that can be made in a design strategy focused either on maximum efficiency or on the minimization of the system inertia. The aerodynamic optimization has been carried out with an in-house CFD 3D code, while the turbine coupling with the engine has been obtained by embedding the aerodynamic maps into the 1D engine model. The analysis showed that the new focus on the transitory response modified substantially the conventional design of the turbine, leading to new geometries able to improve notably the overall performance of the turbocharger.

Calibration of a V-Cone for Low Mass Flows for Small Core Compressor Research

2020 ◽  
Author(s):  
Julia E. Stephens ◽  
Sameer Kulkarni
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Flow Rates ◽  
Turbofan Engines ◽  
Mass Flow Rates ◽  
Low Mass ◽  
Mass Flows ◽  
Multistage Axial Compressor

Abstract Advancements in core compressor technologies are necessary for next generation, high Overall Pressure Ratio (OPR) turbofan engines. High pressure compressors (HPCs) for future engines are being designed with exit corrected mass flow rates less than 2.25 kg/s (5 lbm/s). In order to accurately measure the performance of these advanced designs, high accuracy measurements are needed in test facilities. The W7 High Speed Multistage Axial Compressor Facility at NASA Glenn Research Center has been used to acquire data for advanced compressor designs. This facility utilizes an advanced differential pressure flow meter called a V-Cone. The facility has historically tested components with physical mass flow rates in the range of 27 to 45 kg/s (60 to 100 lbm/s). As such, when the V-Cone was calibrated prior to installation, the calibrations focused on higher mass flow rates, and uncertainties in that regime range from 0.5% to 0.85%. However, for low mass flow rates under 9 kg/s (20 lbm/s), expected in tests of advanced high OPR HPCs rear stages, the uncertainties of the V-Cone exceed 2.5%. To address this, using a method similar to that utilized by the National Institute of Standards and Technology, an array of Critical Flow Venturi Nozzles (CFVs) was installed in the W7 test section and used to calibrate the V-Cone in 0.5 kg/s (1 lbm/s) increments up to 10.5 kg/s (23 lbm/s). This effort details the measurements and uncertainties associated with this calibration which resulted in a final uncertainty of the V-Cone measurements under 1%.

scholarly journals Experimental and Numerical Assessment of the Impact of an Integrated Active Pre-Swirl Generator on Turbocharger Compressor Performance and Operating Range

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3537
Author(s):  
Charles Stuart ◽  
Stephen Spence ◽  
Sönke Teichel ◽  
Andre Starke
Keyword(s):  
Mass Flow ◽  
Operating Conditions ◽  
Centrifugal Impeller ◽  
Boost Pressure ◽  
Flow Rates ◽  
Operating Range ◽  
Surge Margin ◽  
Mass Flow Rates ◽  
Low Mass ◽  
The Impact

The implementation of increasingly stringent emissions and efficiency targets has seen engine downsizing and other complementary technologies increase in prevalence throughout the automotive sector. In order to facilitate ongoing improvements associated with the use of these strategies, delivering enhancements to the performance and stability of the turbocharger compressor when operating at low mass flow rates is of paramount importance. In spite of this, a few concepts (either active or passive) targeting such aims have successfully transitioned into use in automotive turbochargers, due primarily to the requirement for a very wide compressor-operating range. In order to overcome the operational limitations associated with existing pre-swirl generation devices such as inlet guide vanes, this study developed a concept comprising of an electrically driven axial fan mounted upstream of a standard automotive turbocharger centrifugal compressor. Rather than targeting a direct contribution to compressor boost pressure, the fan was designed to act as a variable pre-swirl generation device capable of being operated completely independently of the centrifugal impeller. It was envisioned that this architecture would allow efficient generation of the large pre-swirl angles needed for compressor surge margin extension and efficiency enhancement at low mass flow rate-operating points, while also facilitating the delivery of zero pre-swirl at higher mass flow rates to ensure no detrimental impact on performance at the rated power point of the engine. Having progressed through 1-D and 3-D aerodynamic modelling phases to understand the potential of the system, detailed component design and hardware manufacture were completed to enable an extensive experimental test campaign to be conducted. The experimental results were scrutinized to validate the numerical findings and to test the surge margin extension potential of the device. Compressor efficiency improvements of up to 3.0% pts were witnessed at the target-operating conditions.

Numerical Analysis of an Alternate Stall in a Radial Vaned Diffuser

2016 ◽  
Author(s):  
E. Benichou ◽  
I. Trébinjac
Keyword(s):  
Flow Pattern ◽  
Flow Structure ◽  
Channel Flow ◽  
Mass Flow ◽  
Computational Domain ◽  
Flow Rates ◽  
Operating Range ◽  
Stable Operating ◽  
Mass Flow Rates ◽  
Low Mass

The flow structure in the radial diffuser of a centrifugal compressor is analyzed from steady and unsteady Reynolds-Averaged Navier Stokes (RANS) simulations performed at one rotation speed for which two stable operating ranges separated by an unstable zone have been experimentally experienced. Below a given mass flow rate, close to the peak efficiency point, phase-lagged single-passage simulations do not converge properly anymore. A low frequency appears in the CFD, which cannot be associated with any physical phenomenon. The computational domain is then extended, so that several passages of both the impeller and the diffuser are taken into account. At intermediate mass flow rates, an unstable operating range exists and simulations cannot converge properly either. Nevertheless, if the compressor is further throttled, another stable operating range is obtained at low mass flow rates. The flow structure in that stable operating range is rather unusual: an internal periodicity emerges inside the radial diffuser, involving a two-channel flow pattern. This two-channel flow pattern is found to be stable and fixed in time. Moreover, the phase shift between two adjacent channel pairs happens to be constant. This indicates that a new space – time periodicity is established at low mass flow rates, which involves groups of two passages in the radial diffuser. It is confirmed thanks to a new phase-lagged simulation including one impeller passage and two diffuser passages which shows a good convergence and which gives the same results, both in terms of performance and flow physics.

Numerical Investigations of Flow Features in a Low Pressure Steam Turbine Last Stage Under Different Mass Flow Rates

2015 ◽  
Author(s):  
Bo Liu ◽  
Jiandao Yang ◽  
Daiwei Zhou ◽  
Xiaocheng Zhu ◽  
Zhaohui Du
Keyword(s):  
Steam Turbine ◽  
Mass Flow ◽  
Aerodynamic Force ◽  
Flow Patterns ◽  
Current Paper ◽  
Flow Rates ◽  
Flow Features ◽  
Mass Flow Rates ◽  
Low Mass ◽  
Last Stage

In steam turbine plants, the last stages of the low pressure (LP) turbines can deliver up to 20% of the overall power of the plant. It poses lots of challenges to designers especially when the last stages are operated under low volume flow conditions. In the current paper, numerical simulations are conducted to investigate the flow features in a LP steam turbine. In steady calculations, flows under six different mass flow rates are simulated. Performances and flow patterns in last stage rotor (LSR) in low mass flow rates are highlighted. Since the last stage is modeled as a full blade annulus, flow patterns and blade force in circumferential distribution are examined. Results show that under low mass flow rate conditions, vortices occur in the last stage and the diffuser. The LSR acts like a compressor. The periodical distributions of pressure in LSR passages are broken. High amplitude aerodynamic force fluctuations are found on LSR blades in low mass flow cases. By conducting unsteady simulations, the time series of aerodynamic force are demonstrated to have the similar trend and magnitude of that in steady spatial sequence. The mechanism for aerodynamic force excitation is discussed in the current paper. Unsteady pressure fluctuation in tip section of LSR at low mass flow rates seems to have a significant correlation with the aerodynamic force fluctuation level rise.

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