CFD Analysis of the Unsteady Flow in a Two-Stage Axial Turbine

2016 ◽  
Author(s):  
Yang Pan ◽  
Qi Yuan ◽  
Qian Chen ◽  
Qing Ge ◽  
Dawei Ji
Keyword(s):  
Unsteady Flow ◽  
Rotational Speed ◽  
High Speed ◽  
Stokes Equations ◽  
Great Influence ◽  
Two Stage ◽  
Lower Efficiency ◽  
Axial Turbine ◽  
Partial Admission ◽  
Mode A

Partial admission, which has the advantage of avoiding large losses while the turbine at low load operations, is widely used in regulating the power of turbomachinery. However, partial admission causes prominent unsteady flow, additional exciting forces and extra losses. Thus, it has great significance to investigate the characteristics of partial admission turbines. In this paper, efficiency and unsteady flow performance of a small two-stage subsonic axial turbine with partial admission are analyzed. Firstly, a 3-D model with four discontinuous equally-distributed nozzle blocks was built, and the computational grid, which only consisted of hexahedral mesh, was generated. Reynolds Averaged Navier-Stokes equations were solved by commercial software ANSYS-CFX and the RNG k-ε turbulence model was adopted. Secondly, to investigate the influence of admission modes, two partial admission modes (A-two diagonal valve opening; B-two adjacent valves opening) were analyzed separately and compared with the full admission situation (Mode C). Finally, the turbine performances in Mode A and B at other speeds (75% and 110% of rated speed) were analyzed and pressure distributions at three different heights (10%, 50% and 90% of the blade height) were investigated in detail. The results indicated that partial admission could cause extra mixture losses and lead to lower efficiency. Among these kinds of modes, full admission (Mode C) performed best in efficiency, and Mode B performed better than Mode A under partial admission conditions. Furthermore, strong non-uniformity was found in circumferential direction and large pressure drop occurred at the gap between two admission blocks due to expansion effects. The computational results also showed that the flow parameter fluctuations attenuated evidently in the downstream stages and the pressure vibration mainly occurred after nozzle stages. Strong vortices and backflow can be noticed at the pressure side of the active nozzle boxes. Additionally, the rotational speed has a great influence on the performance of turbine. Higher rotational speed led to bigger efficiency and smoother pressure distribution. And the alteration trend becomes slow at high speed.

scholarly journals Investigation of the Optimum Clocking Position in a Two-Stage Axial Turbine

2005 ◽  
Vol 2005 (3) ◽  
pp. 202-210 ◽  
Author(s):  
Dieter Bohn ◽  
Sabine Ausmeier ◽  
Jing Ren
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Preliminary Design ◽  
Two Stage ◽  
Axial Turbine ◽  
Sliding Mesh ◽  
Field Distributions ◽  
Unsteady Simulation

A frozen rotor approach in a steady calculation and a sliding mesh approach in an unsteady simulation are performed in a stator clocking investigation. The clocking is executed on the second stator in a two-stage axial turbine over several circumferential positions. Flow field distributions as well as the estimated performances from two approaches are compared with each other. The optimum clocking positions are predicted based on the estimated efficiency from the two approaches. The consistence of the optimum clocking positions is discussed in the paper. The availability and the limit of the frozen rotor approach in predicting the optimum clocking position is analyzed. It is concluded that the frozen rotor approach is available to search the optimum clocking position in the preliminary design period, although it misses some features of the unsteady flow field in the multistage turbines.

The 2-Stage Axial Turbine Test Facility “LISA”

2001 ◽  
Author(s):  
M. Sell ◽  
J. Schlienger ◽  
A. Pfau ◽  
M. Treiber ◽  
R. S. Abhari
Keyword(s):  
Unsteady Flow ◽  
Mass Flow ◽  
Measurement Techniques ◽  
Operating Conditions ◽  
Test Facility ◽  
Two Stage ◽  
Axial Turbine ◽  
Aerodynamic Pressure ◽  
Second Stage ◽  
The Impact

This paper describes the design and construction of a new two stage axial turbine test facility, christened “Lisa”. The research objective of the rig is to study the impact (relevance) of unsteady flow phenomena upon the aerodynamic performance, this being achieved through the use of systematic studies of parametric changes in the stage geometry and operating point. Noteworthy in the design of the rig is the use of a twin shaft arrangement to decouple the stages. The inner shaft carries the load from the first stage whilst the outer is used with an integral torque-meter to measure the loading upon the second stage alone. This gives an accurate measurement of the loading upon the aerodynamically representative second stage, which possesses the correct stage inlet conditions in comparison to the full two stage machine which has an unrealistic axial inlet flow at the first stator. A calibrated Venturi nozzle measures the mass flow at an accuracy of below 1%, from which stage efficiencies can be derived. The rig is arranged in a closed loop system. The turbine has a vertical arrangement and is connected through a gear box to a generator system that works as a brake to maintain the desired operating speed. The turbine exit is open to ambient pressure. The rig runs at a low pressure ratio of 1.5. The maximum Mach number at stator exit is 0.3 at an inlet pressure of 1.5 bar. The maximum mass flow is 14 kg/sec. Nominal rotor design speed is 3000 RPM. The tip to hub blade ratio is 1.29, and the nominal axial chord is 50 mm. The rig is designed to accommodate a broad range of measurement techniques, but with a strong emphasis upon unsteady flow methods, for example fast response aerodynamic pressure probes for time-resolved flow measurements. The first section of this paper describes the overall test facility hardware. This is followed by a detailed focus on the torque measurement device including stage efficiency measurements at operating conditions in Lisa. Discussion of measurement techniques completes the paper.

scholarly journals Refrigeration Process With High Speed Technology

1998 ◽  
Author(s):  
Maunu Kuosa ◽  
Jari Backman ◽  
Timo Talonpoika ◽  
Petri Sallinen ◽  
Jaakko Larjola ◽  
...  
Keyword(s):  
Rotational Speed ◽  
High Speed ◽  
Cooling Capacity ◽  
Working Fluid ◽  
Pascal Program ◽  
Two Stage ◽  
Program Unit ◽  
Fluid Properties ◽  
Industrial Refrigeration ◽  
Process Calculation

The aim of this study was to make a computer program that simulates a standard refrigeration process, and a process provided with a bubble intercooler. A further object of the study was to establish the suitability of a turbocompressor for small refrigeration plants. Firstly the fundamentals of refrigeration machines and industrial refrigeration systems are discussed. An iteration procedure of steady state refrigeration process calculation is introduced. Fluid properties are calculated with the program units created for the modelling of an ORC power plant. Specific input files were made for 6 process fluids R134a, R123, isopentane, isobutane, toluene and ammonia. The compressor program is linked to the refrigeration process simulation program in order to model single stage and two stage radial compressors. The Turbo Pascal program made for microcomputers is modular, which makes it possible to develop and test the program unit by unit. The maximum deviations of fluid properties from those in tables was found to be less than 1 per cent. To simulate tailor-made refrigeration plants, a simple model is required. On nominal loads the program estimates an optimum intermediate pressure for the bubble process and optimum rotational speed for the radial compressor(s). The lowering of the rotational speed by an inverter gives high COP-values on partial loads of the plant. Based on the example calculation, a two stage turbocompressor calculated with isopentane as the working fluid, a cooling capacity of 1200 W seems to be feasible.

Unsteady Flow About a Solid Cylinder Falling Through a Viscous Fluid Contained in a Vertical Tube

1971 ◽  
Vol 93 (4) ◽  
pp. 518-523
Author(s):  
C. C. Shih ◽  
Rao V. S. Yalamanchili
Keyword(s):  
Viscous Fluid ◽  
Unsteady Flow ◽  
High Speed ◽  
Stokes Equations ◽  
Vertical Tube ◽  
Time Dependent ◽  
Polar Coordinates ◽  
Navier Stokes ◽  
Solid Cylinder ◽  
Eigen Values

This study is concerned with the unsteady flow field developed in a viscous fluid contained in a vertical tube by a solid cylinder of considerable length falling vertically from rest in the tube. Based on simplifying assumptions, the Navier-Stokes equations are linearized and reduced to a time-dependent one dimensional equation in cylindrical polar coordinates. A solution of the equation preceded by the determination of eigen values from boundary conditions peculiar to the problem of interest has yielded time-dependent velocity profiles across an axisymmetric cross-section of laminar flow in the annular space and other physical quantities related to the flow phenomena about the falling cylinder. Example problems were solved with the use of an electronic digital computer and the numerical results are presented in both tabular and graphical forms. In addition, a simple experiment of the flow system was performed and recorded on high speed movie films. The experimental results have verified reasonably well the theoretical results.

Meshing Method of Calculating Water-Entry Flow Field at High Speed

2013 ◽  
Vol 300-301 ◽  
pp. 1144-1147
Author(s):  
Zhu Zhu ◽  
Xu Long Yuan ◽  
Ya Dong Wang ◽  
Yun Ju Yan
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Unsteady Flow ◽  
High Speed ◽  
Great Influence ◽  
Water Entry ◽  
Unsteady Process ◽  
Natural Cavitation ◽  
Multi Phase

An important part of the numerical simulation is the grid which the quality has great influence on the calculation precision, and also the influence often is crucial factor in most of situation. Water-entry at high speed is a complex unsteady process, and its numerical simulation needs to take consider of natural cavitation as well as rotation of the underwater body. In this paper, a new meshing method was given with using the Layering, Smoothing and Remeshing for calculating the unsteady flow field. Numerical simulation shows that the mesh given in this paper has better quality, and can be used to calculate the multi-phase mode of water-entry at the high speed.

scholarly journals DEVELOPMENT AND EVALUATION OF FINGER WHEEL AND CUTTING DISC COMBINED DEVICE FOR STALK RETURNING

2021 ◽  
pp. 54-64
Author(s):  
Zhilong Zhang ◽  
Yongtao Yu ◽  
Qiyong Yang ◽  
Aijun Geng ◽  
Ji Zhang
Keyword(s):  
Rotational Speed ◽  
High Speed ◽  
Great Influence ◽  
Orthogonal Test ◽  
National Standard ◽  
High Speed Photography ◽  
Test Results ◽  
Cutting Power ◽  
Feeding Speed ◽  
Verification Test

Stalk returning technology was an important way to preserve soil nutrients and reduce soil erosion. It was of great significance to improve the stalk chopping quality, reduce power consumption. On the basis of the previous research, the finger wheel and cutting disc combined device for stalk returning was developed, mainly composed of the sawtooth blade group, the finger wheel and the stalk lifting grid. The stalk was fed into the cutting area of the sawtooth blades by the rotation of the finger wheel, and the operation of the stalk chopping was completed under the combination of the sawtooth blade group and the finger wheel. The movement of stalks in the device with finger wheel and sawtooth blades was analysed by high speed photography, and the rotational speed of finger wheel, the rotational speed of sawtooth blade group, the stalk feeding speed had a great influence on the movement of the stalks. Through orthogonal test and verification test, the clamping angle was 20°, the rotational speed of sawtooth blade group was 800 min-1, the stalk feeding speed was 1.45 m/s, the rotational speed of finger wheel was 110 min-1, the cut length qualified rate was 92.47% and the cutting power was 529.97 W. The test results met the quality requirements of the Chinese national standard. The related research can provide reference for the research of stalk returning device.

Computation of unsteady flow through steam turbine blade rows at partial admission

1997 ◽  
Vol 211 (3) ◽  
pp. 197-205 ◽  
Author(s):  
L He
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Stokes Equations ◽  
Computational Study ◽  
Guide Vane ◽  
Three Dimensional ◽  
Admission Rate ◽  
Inlet Guide Vane ◽  
Flow Equations ◽  
Partial Admission

Partial admission in the steam turbine is associated with strong unsteady flow effects on aerodynamic performance. This paper presents a first-of-its-kind computational study of the problem. The unsteady flow field in multiple blade passages and multiple blade rows is governed by the quasi three-dimensional unsteady Navier-Stokes equations, closed by a mixing-length turbulence model. The partial admission is introduced by blocking one segmental arc (or several segmental arcs) of the inlet guide vane of the first stage. The flow equations are solved by using a time-dependent finite volume method. The calculated unsteady force on rotor blades for a turbine stage at partial admission compares well with the corresponding experimental data. The present results show that a cyclic pumping and sucking phenomenon occurs in the rotor blade row of the first stage, resulting in large unsteady loading and marked mixing loss. For a single stage at a given admission rate, a blocking arrangement with two flow segments is shown to be much more detrimental than one arc of admission, because of the extra mixing loss. The results for a two-stage case, however, suggest that the decaying rate of circumferential non-uniformities could be far more important for performance. For this reason, an enhanced mixing loss in the first stage might be beneficial to the overall efficiency of a multistage turbine.

Study on the Steady and Unsteady Aerodynamic Performance of a Radial Inflow Turbine With Small Partial Admission in a Miniature ORC System

2011 ◽  
Author(s):  
Ping Li ◽  
Jianhui Chen ◽  
Di Zhang ◽  
Yonghui Xie
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotational Speed ◽  
Rankine Cycle ◽  
Maximum Efficiency ◽  
Unsteady Aerodynamic ◽  
Radial Turbine ◽  
Partial Admission ◽  
Excitation Force ◽  
Radial Inflow Turbine

There is a great deal of residual heat under 350 °C being released into environment, without being used efficiently. Compared to the Rankine cycle with water as its working substance, it is effective to utilize Organic Rankine Cycle (ORC) to recover these waste heats. In the threshold of this paper, a miniature ORC system is proposed, and maximum efficiency of the system is achieved by means of optimal working substance. Moreover, numerical simulation of the partial admission (ε = 0.267) high rotational speed radial inflow turbine, which is the key unit in the system, is fulfilled. At the operating rotational speed of 60000 rpm and the proposed thermodynamic parameters, steady and unsteady flow field in the turbine are investigated with R11 as working fluid. The detailed parameters, such as axial force of rotor, power generated and thermal efficiency of the radial turbine, are analyzed. In addition, the unsteady flow pressure is integrated around the rotor blade profile to provide the unsteady aerodynamic blade force. And subsequently frequencies of unsteady disturbances and excitation force factors are obtained by spectrum analysis, which are of key importance for blade response analysis. The generation, development and dissipation process of the secondary flows, passage vortex and leakage vortex are observed in the flow channel. The results reveal that the partial admission greatly influences the parameters distributions in the flow field and the losses of radial turbine mainly occur at the frontier of the passage in the vicinity of blade root. As is discussed in the analysis of excitation force factor, the radial turbine is safe in the operation. The results discussed in this paper are beneficial for the sequent optimization and manufacture of the miniature turbine.

scholarly journals High-Speed 3D Printing of High-Performance Thermosetting Polymers via Two-Stage Curing

2018 ◽  
Vol 39 (7) ◽  
pp. 1700809 ◽  
Author(s):  
Xiao Kuang ◽  
Zeang Zhao ◽  
Kaijuan Chen ◽  
Daining Fang ◽  
Guozheng Kang ◽  
...  
Keyword(s):  
3D Printing ◽  
High Speed ◽  
High Performance ◽  
Two Stage ◽  
Thermosetting Polymers

Advances in coupled axial turbine and nonaxisymmetric exhaust volute aerodynamics for turbomachinery

2020 ◽  
pp. 095441002096645
Author(s):  
Jie Gao ◽  
Chunde Tao ◽  
Dongchen Huo ◽  
Guojie Wang
Keyword(s):  
Performance Improvement ◽  
High Efficiency ◽  
Three Dimensional ◽  
Great Influence ◽  
Aerodynamic Characteristics ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Axial Turbine ◽  
Flow Interactions ◽  
And Performance

Marine, industrial, turboprop and turboshaft gas turbine engines use nonaxisymmetric exhaust volutes for flow diffusion and pressure recovery. These processes result in a three-dimensional complex turbulent flow in the exhaust volute. The flows in the axial turbine and nonaxisymmetric exhaust volute are closely coupled and inherently unsteady, and they have a great influence on the turbine and exhaust aerodynamic characteristics. Therefore, it is very necessary to carry out research on coupled axial turbine and nonaxisymmetric exhaust volute aerodynamics, so as to provide reference for the high-efficiency turbine-volute designs. This paper summarizes and analyzes the recent advances in the field of coupled axial turbine and nonaxisymmetric exhaust volute aerodynamics for turbomachinery. This review covers the following topics that are important for turbine and volute coupled designs: (1) flow and loss characteristics of nonaxisymmetric exhaust volutes, (2) flow interactions between axial turbine and nonaxisymmetric exhaust volute, (3) improvement of turbine and volute performance within spatial limitations and (4) research methods of coupled turbine and exhaust volute aerodynamics. The emphasis is placed on the turbine-volute interactions and performance improvement. We also present our own insights regarding the current research trends and the prospects for future developments.

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