Numerical Study of the Effect of Multiple Tightly-Wound Vortices on a Transonic Fan Stage Performance

2014 ◽  
Author(s):  
Alejandro Castillo Pardo ◽  
Ahad Mehdi ◽  
Vassilios Pachidis ◽  
David G. MacManus
Keyword(s):  
Mass Flow ◽  
Vortex Flow ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Close Relation ◽  
Critical Value ◽  
Engine Design ◽  
Wide Range ◽  
Inlet Conditions ◽  
Transonic Fan

As a result of the new engine design trends, the likelihood of tightly-wound vortices being ingested by the engine rises. Therefore, the risk associated with the ingestion of swirl distortion becomes a major concern. A numerical analysis of the response of a transonic fan stage to the ingestion of different distorted flow patterns is carried out using steady-state CFD. The CFD approach is generated and validated against experimental data for undistorted inlet conditions. Following the validation, a wide range of configurations with vortex flow distortions are analysed and evaluated. The change in global performance is quantified and the flow field is extensively analysed. Consequently, the parameters that have the most critical impact on the performance of the fan stage are identified. The study identifies a close relation between the number of vortices ingested and the change in rotor performance. However, the deviation from the clean rotor performance has been found to be independent of the circumferential distance between vortices. Additionally, the effects of the radial location, polarity and vortex magnitude have been assessed. Ingested co-rotating vortices cause a significant reduction in pressure ratio and corrected mass flow. In contrast, counter-rotating vortices are associated with an increase in the pressure ratio and corrected mass flow. The change in rotor performance increases with the strength. However, a dramatical drop in pressure ratio is observed for counter-rotating vortices when the vortex strength exceeds a critical value.

Numerical Study of Aerodynamic Losses of Effusion Cooling Holes in Aero-Engine Combustor Liners

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
A. Andreini ◽  
A. Bonini ◽  
G. Caciolli ◽  
B. Facchini ◽  
S. Taddei
Keyword(s):  
Mass Flow ◽  
Cooling System ◽  
Numerical Study ◽  
Numerical Data ◽  
Good Reliability ◽  
Data Set ◽  
Discharge Coefficients ◽  
Wide Range ◽  
Depth Analysis ◽  
Aero Engine

Due to the stringent cooling requirements of novel aero-engines combustor liners, a comprehensive understanding of the phenomena concerning the interaction of hot gases with typical coolant jets plays a major role in the design of efficient cooling systems. In this work, an aerodynamic analysis of the effusion cooling system of an aero-engine combustor liner was performed; the aim was the definition of a correlation for the discharge coefficient (CD) of the single effusion hole. The data were taken from a set of CFD RANS (Reynolds-averaged Navier-Stokes) simulations, in which the behavior of the effusion cooling system was investigated over a wide range of thermo/fluid-dynamics conditions. In some of these tests, the influence on the effusion flow of an additional air bleeding port was taken into account, making it possible to analyze its effects on effusion holes CD. An in depth analysis of the numerical data set has pointed out the opportunity of an efficient reduction through the ratio of the annulus and the hole Reynolds numbers: The dependence of the discharge coefficients from this parameter is roughly linear. The correlation was included in an in-house one-dimensional thermo/fluid network solver, and its results were compared with CFD data. An overall good agreement of pressure and mass flow rate distributions was observed. The main source of inaccuracy was observed in the case of relevant air bleed mass flow rates due to the inherent three-dimensional behavior of the flow close to bleed opening. An additional comparison with experimental data was performed in order to improve the confidence in the accuracy of the correlation: Within the validity range of pressure ratios in which the correlation is defined (>1.02), this comparison pointed out a good reliability in the prediction of discharge coefficients. An approach to model air bleeding was then proposed, with the assessment of its impact on liner wall temperature prediction.

Numerical Method for Studying Bearing Gap Pressure Wave Development and Subsequent Performance Mapping of Externally Pressurized Gas Journal Bearings

2019 ◽  
Author(s):  
Tom M. Lawrence ◽  
Marvin D. Kemple
Keyword(s):  
Numerical Method ◽  
Cross Section ◽  
Mass Flow ◽  
Pressure Wave ◽  
Design Space ◽  
Numerical Study ◽  
Pressure Waves ◽  
Wide Range ◽  
Wave Development ◽  
Static Instability

Abstract In previous work, numerical methods were developed to determine the pressure waves (pressure distribution) in the bearing gap of round externally pressurized gas bearings (EPB’s) that were pressurized through porous liners (PL bearings) or through liners with rows of feedholes (FH bearings). When integrated and differentiated these pressure portraits yield the net hydrodynamic force (FH) between the shaft and the bushing and the mass flow rates through the bearing gap. These results successfully replicated force-deflection curves and mass flow rate data for experimentally tested prototype FH and PL bearings over a wide range of mass flow constriction and clearances. Subsequently the numerical study was expanded to a broader design space of clearance and mass flow compensation. Also, a bearing performance mapping method of mapping the normalized bearing load over the clearance-eccentric deflection plane was developed for different levels of mass compensation. These performance maps produced a very interesting result as they indicated certain areas in the design space of FH bearings where static instability (negative stiffness) would be encountered. This static instability was not observed in the experimental data but is noted in references as known to occur in practice. Because this numerical method is based on the development of pressure wave portraits, the FH pressure wave could then be “dissected” in the areas of the onset of static instability which gave much insight as to the possible causes of static instability. This initial work, then, was perhaps the first to predict where in design space static instability would occur and yield some insight via examination of the corresponding pressure waves as to the cause. The numeric techniques developed, however are in no way limited to non-rotating bearings but are extensible to rotating bearings. The method is also easily extensible to examination of any configuration of feedholes or orifices. Nor is it limited to parallel deflections but can yield results for unbalanced loads. The method is also not limited to round bearings but can be applied to any cross-section configuration of bearing gap cross section such as a 3 lobed bearing or a slotted 3 lobed bearing. Examination of the resulting pressure wave development patterns for different scenarios can be examined to garner insight as to the causes of differing performance that can be applied to alterations towards optimization. Thus sharing in detail the developed numerical method underlying these studies seems worthwhile.

Numerical Performance and Flow Field Study of Centrifugal Compressor With Supercritical Carbon-Dioxide (SCO2)

2019 ◽  
Author(s):  
Hemant Kumar ◽  
Chetan S. Mistry
Keyword(s):  
Carbon Dioxide ◽  
Thermodynamic Properties ◽  
Critical Point ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Compressor Inlet

Abstract The Supercritical carbon-dioxide Brayton cycle main attraction is due to the Supercritical characteristic of the working fluid, carbon-dioxide (SCO2). Some of the advantages of using SCO2 are relatively low turbine inlet temperature, the compression work will be low, and the system will be compact due to the variation of thermodynamic properties (like density, and specific heat ratio) of SCO2 near the critical point. SCO2 behave more like liquid when its state is near the critical point (Total Pressure = 7.39 MPa, Total Temperature = 305 K), operating compressor inlet near critical point can minimize compression work. For present study the centrifugal compressor was designed to operate at 75,000 rpm with pressure ratio (P.R) = 1.8 and mass flow rate = 3.53 kg/s as available from Sandai report. Meanline design for centrifugal compressor with SCO2 properties was done. The blade geometry was developed using commercial CAD Ansys Bladegen. The flow domain was meshed using Ansys TurboGrid. ANSYS CFX was used as a solver for present numerical study. The thermodynamic properties of SCO2 were imported from the ANSYS flow material library using SCO2.RPG [NIST thermal physics properties of fluid system]. In order to ensure the change in flow physics the mesh independence study was also conducted. The present paper discuss about the performance and flow field study targeting different mass flow rates as exit boundary condition. The comparison of overall performance (Pressure Ratio, the Blade loading, Stage efficiency and Density variation) was done with three different mass flow rates. The designed and simulated centrifugal compressor meets the designed pressure rise requirement. The variation of mass flow rate on performance of centrifugal compressor was tend to be similar to conventional centrifugal compressor. The paper discusses about the effect of variation in density, specific heat ratio and pressure of SCO2 with different mass flow outlet condition. The performance map of numerical study were validated with experiment results and found in good agreement with experimental results. The change in flow properties within the rotor flow passage are found to be interesting and very informative for future such centrifugal compressor design for special application of SCO2 Brayton cycle. 80% mass flow rate has given better results in terms of aerodynamic performance. Abrupt change in thermodynamic properties was observed near impeller inlet region. Strong density variations are observed at compressor inlet.

Assessment of Dimensionless Correlations for Prediction of Refrigerant Mass Flow Rate Through Capillary Tubes — A Review

2017 ◽  
Vol 25 (04) ◽  
pp. 1730004 ◽  
Author(s):  
Mehdi Rasti ◽  
Ji Hwan Jeong
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Capillary Tube ◽  
Capillary Tubes ◽  
Two Phase ◽  
Comprehensive Review ◽  
Wide Range ◽  
Inlet Conditions ◽  
Dimensionless Correlations

Capillary tubes are widely used as expansion devices in small-capacity refrigeration systems. Since the refrigerant flow through the capillary tubes is complex, many researchers presented empirical dimensionless correlations to predict the refrigerant mass flow rate. A comprehensive review of the dimensionless correlations for the prediction of refrigerants mass flow rate through straight and coiled capillary tubes depending on their geometry and adiabatic or diabatic capillary tubes depending on the flow configurations has been discussed. A comprehensive review shows that most of previous dimensionless correlations have problems such as discontinuity at the saturated lines or ability to predict the refrigerant mass flow rate only for the capillary tube subcooled inlet condition. The correlations suggested by Rasti et al. and Rasti and Jeong appeared to be general and continuous and these correlations can be used to predict the refrigerant mass flow rate through all the types of capillary tubes with wide range of capillary tube inlet conditions including subcooled liquid, two-phase mixture, and superheated vapor conditions.

A Parametric Numerical Study of the Effects of Inlet Swirl Distortion on a Transonic Compressor Stage

2013 ◽  
Author(s):  
Taieb Ben Sghaier ◽  
Ahad Mehdi ◽  
Vassilios Pachidis ◽  
David MacManus
Keyword(s):  
Numerical Study ◽  
Pressure Ratio ◽  
Underlying Mechanism ◽  
Aerodynamic Characteristics ◽  
Vortical Flow ◽  
Compressor Stage ◽  
Significant Drop ◽  
Transonic Compressor ◽  
Wide Range ◽  
Compressor Performance

The ingestion or manifestation of a vortical flow can have dramatic effects on an aero engine. It is therefore imperative to quantify these effects and understand their underlying mechanism. This numerical study analyses the response of a transonic compressor stage to the ingestion of different streamwise vortical distortions using steady-state CFD. The vortex is described using a number of features, which are varied and combined together in order to generate a wide range of different swirl disturbances. The initial aim of this research is to identify the vortex features which have the highest impact on compressor performance. A numerical model of a compressor stage is generated which enables prescribed vortical flows to be imposed at the domain inlet. The method is validated against experimental data which was obtained under clean, undistorted conditions. The response of the compressor following the ingestion of a vortex is assessed both in terms of overall compressor performance parameters as well as more detailed aerodynamic characteristics. The results show that the compressor is sensitive to the vortex magnitude, core size, polarity and radial location. Furthermore, co-rotating, high-strength vortices which are ingested in the near-hub region cause the most significant drop in pressure ratio and corrected mass flow. In contrast, counter-rotating vortices cause little change in compressor performance. Overall, the work shows that modest swirl distortions can have a notable impact on the compressor performance and stability, and highlights the growing need to develop methods and an understanding of how this class of distortion can be evaluated during the engine design phase.

scholarly journals Low pressure ratio transonic fan stall with radial distortion

2020 ◽  
Vol 4 ◽  
pp. 226-237
Author(s):  
Tim Williams ◽  
Cesare Hall ◽  
Mark Wilson
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Full Range ◽  
Perforated Plate ◽  
Low Pressure ◽  
Suction Surface ◽  
Stall Inception ◽  
Radial Distortion ◽  
Inlet Conditions ◽  
Transonic Fan

Numerical methods that can predict stall behaviour with non-uniform inlet conditions allow assessment of the stable operating range across flight conditions during the design of fan stages for civil aircraft. To extend the application of methods validated with clean inflow, the effect of a tip low radial distortion on the stall behaviour of a low pressure ratio transonic fan has been investigated using both high speed experiments and 3D URANS computations. The distortion is generated in the experiment using a perforated plate and this is fully represented within the computational mesh. This enables computations to reproduce the full range of flow conditions accurately without adjusting the inlet boundary condition. Both the calculations and measurements show that the presence of the distortion decreases the stall cell rotational speed and increases the cell circumferential extent. In the calculations, the cell speed reduced from 87% to 67% of shaft speed, compared to a change of 82% to 58% in the experiment. With and without distortion, the computations show how stall inception stems from blockage formed by flow separation from the tip-section suction surface, behind the shock. In the distorted case, the more forward shock position produces the blockage further upstream, causing a greater reduction of flow to adjacent passages. This leads to a stall cell in the distorted case that is around 80% larger.

Investigation of Effects of Radial Distortion on Transonic Fan Behavior

2010 ◽  
Author(s):  
Dmytro M. Voytovych ◽  
Guoping Xia ◽  
Chenzhou Lian ◽  
Charles L. Merkle
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Tip Vortex ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Transonic Fan ◽  
Total Pressure Ratio

The flow analysis around blades of a transonic fan is presented for both clean and radially distorted inlets. Computations are shown for four-blade passages that are accomplished with a second order accurate code using a k-ω turbulence model. The mass flow rate along a speed line is controlled by varying a choked nozzle downstream of the fan. The results show good agreement with data for three speed lines. In the near-stall region, the flow first becomes unsteady and then unstable with the unsteadiness increasing at lower speeds. The four-blade simulations remained stable to lower mass flow rates than the single-blade simulations. In the near-stall vicinity, tip vortex breakdown occurred creating a low momentum zone near the blade tip on the pressure side that grew as the mass flow was decreased until it eventually blocked the passage. The presence of distortion reduced the operational range and moved the stall line to higher mass flow rates. At high speeds distortion reduced both the mass flow rate and total pressure ratio while at lower speeds, the choking mass flow rate was reduced, but the total pressure ratio was slightly improved. The flow separation near the hub on the suction side was caused by the distortion. Its size was decreasing with rotational speed.

Numerical study on the Effect of Interaction Vaned Diffuser with Impeller on the Performance of a Modified Centrifugal Compressor

2013 ◽  
Vol 30 (2) ◽  
pp. 113-121 ◽  
Author(s):  
L. H. Jawad ◽  
S. Abdullah ◽  
R. Zulkifli ◽  
W. M. F. W. Mahmood
Keyword(s):  
Centrifugal Compressor ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Internal Flow ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage ◽  
Compressor Impeller ◽  
Inlet Conditions

ABSTRACTThis paper is a numerical simulation that was made in the three-dimensional flow, carried out in a modified centrifugal compressor, having vaned diffuser stage, used as an auto-motive turbo charger. Moreover, the performance of the centrifugal compressor was dependent on the proper matching between compressor impeller and vaned diffuser, influencing significantly surge and the efficiency of centrifugal compressor stages. In addition, a modified compressor impeller, coupled with vane and vaneless diffuser, has been found to have similar internal flow patterns for both the vaneless and vaned diffuser design. The vaned diffuser effect has been paid particular attention in terms of better analysis where the diffuser was designed for high sub-sonic inlet conditions. Another aim of this research was to study and simulate the effect of vaned diffuser on the performance of a centrifugal compressor. The simulation was undertaken by using a commercial software, the so-called ANSYS CFX, to predict numerically the performance in terms of pressure ratio, poly tropic efficiency and mass flow rate for the centrifugal compressor stage. The results were generated from CFD and were analyzed for better understanding of the fluid flow through centrifugal compressor stage. Conclusively, it was observed that the effect of the vaned diffuser is to convert the kinetic energy into a high static pressure after analyzing the results of the simulation.

Numerical Study on the Interaction of Water Mist with a Fire Plume

2011 ◽  
Vol 130-134 ◽  
pp. 1730-1733
Author(s):  
Xiang Di Zhao ◽  
Hong Li Xu ◽  
Xi Shi Wang
Keyword(s):  
Velocity Field ◽  
Droplet Size ◽  
Mass Flow ◽  
Numerical Study ◽  
Critical Value ◽  
Water Mist ◽  
Temperature History ◽  
Fire Plume ◽  
Plume Temperature ◽  
Fluent Software

A numerical study on the interaction of water mist with a fire plume was conducted using FLUENT software. The effects of different mist characteristics, such as droplet size and spray intensity, was considered in this simulation. The fire plume temperature history and velocity field were investigated. The results show that with a certain droplet size of water mist, the extinguishing time will be shorter when the mass flow of water increases, but this effect is no longer distinct after the mass flow of water mist increased to a critical value.

scholarly journals Numerical Study of Multistage Transcritical Organic Rankine Cycle Axial Turbines

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
L. Sciacovelli ◽  
P. Cinnella
Keyword(s):  
Numerical Study ◽  
Pressure Ratio ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Working Fluid ◽  
Dense Gas ◽  
Working Fluids ◽  
Inlet Conditions ◽  
The Impact

Transonic flows through axial, multistage, transcritical organic rankine cycle (ORC) turbines are investigated by using a numerical solver including advanced multiparameter equations of state and a high-order discretization scheme. The working fluids in use are the refrigerants R134a and R245fa, classified as dense gases due to their complex molecules and relatively high molecular weight. Both inviscid and viscous numerical simulations are carried out to quantify the impact of dense gas effects and viscous effects on turbine performance. Both supercritical and subcritical inlet conditions are studied for the considered working fluids. In the former case, flow across the turbine is transcritical, since turbine output pressure is subcritical. Numerical results show that, due to dense gas effects characterizing the flow at supercritical inlet conditions, supercritical ORC turbines enable, for a given pressure ratio, a higher isentropic efficiency than subcritical turbines using the same working fluid. Moreover, for the selected operating conditions, R134a provides a better performance than R245fa.

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