A New Emergency Stop and Control Valve Design: Part 2 — Validation of Numerical Model and Transient Flow Physics

2014 ◽  
Author(s):  
Christian Musch ◽  
Frank Deister ◽  
Gerta Zimmer ◽  
Ingo Balkowski ◽  
Peter Brüggemann ◽  
...  
Keyword(s):  
Steady State ◽  
Mass Flow ◽  
Transient Flow ◽  
Control Valve ◽  
Transient Behavior ◽  
Complex Flow ◽  
Stop Valve ◽  
Turbine Inlet ◽  
Flow Through ◽  
Emergency Stop

In order to enhance steam mass flow through a turbine it becomes necessary to reduce the flow resistance of the turbine inlet valves. Consequently, a replacement of the high pressure turbine inlet valves is required. The valve combination described in this paper consists of a control valve and an emergency stop valve, opposite to the control valve. Both valves share a common valve seat. The control valve is a single-seat valve with integral pilot disc. A pre-stoke is introduced to allow for moderate opening forces. The emergency stop valve closes in countercurrent with the steam mass flow. The flow through the valve is analyzed by steady state and transient computational flow simulations. In addition to the steam mass flow, the forces acting upon the valve are determined. Transient behavior will be investigated by means of analyzing pressure fluctuations. Therefore frequencies caused by the steam flow are determined in the range up to 2000Hz. It will be shown that neither steady state nor transient simulations with a simple eddy viscosity turbulence model are capable to correctly predict the complex flow inside the valve. More sophisticated turbulence modeling like Large-Eddy simulation is thus inevitable. Furthermore, the physical phenomena causing the transient behavior are discussed. All findings are verified by comparison of the CFD with the measurements.

The Transient Response of Orifices and Very Short Lines

1972 ◽  
Vol 94 (2) ◽  
pp. 483-489 ◽  
Author(s):  
J. E. Funk ◽  
D. J. Wood ◽  
S. P. Chao
Keyword(s):  
Steady State ◽  
Pressure Drop ◽  
System Analysis ◽  
Transient Flow ◽  
Transient Behavior ◽  
Short Term ◽  
State Equations ◽  
Steady State Condition ◽  
Orifice Flow ◽  
Flow Through

It is generally assumed that orifices and valves follow closely their steady-state characteristics during transient operation. However, this assumption of quasisteady behavior may lead to errors in predicting transient flow conditions under certain circumstances. In order to evaluate the transient behavior of an orifice, a differential equation relating the flow through and the pressure drop across an orifice was derived. An extension was made to include an axial dimension for the orifice. The solution of this equation for transient flow through an orifice subjected to a step change in pressure drop across the orifice is significantly different than that obtained using the steady state relationship. An experiment was designed to evaluate the theoretical results in which an orifice on the end of a line was subjected to a sudden pressure change and the resulting transient pressures were observed. It was found that a significant short term transient occurs before the orifice flow reaches the new steady state condition. The observed short term transient agrees well with that predicted by the theory. It is concluded that the behavior of an orifice can deviate considerably from that predicted by steady-state equations during periods of rapid pressure or flow changes. The dynamic description of orifice flow may be combined with a larger system analysis (e.g., using the method of characteristics) to more accurately predict the overall transient performance of flow systems.

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.

Steady and Transient Flow of a Non-Newtonian Chemically Reactive Fluid in a Twin-Screw Extruder

2001 ◽  
Author(s):  
W. Zhu ◽  
Y. Jaluria
Keyword(s):  
Steady State ◽  
Response Time ◽  
Transient Flow ◽  
Transient Behavior ◽  
Operating Conditions ◽  
Twin Screw Extruder ◽  
Screw Extruder ◽  
Twin Screw ◽  
Calculated Velocity ◽  
Screw Extruders

Abstract The flow of chemically reactive non-Newtonian materials, such as bio-polymers and aciylates, in a fully intermeshing, co-rotating twin-screw extruder is numerically investigated. A detailed study of the system transient behavior is carried out. The main transient aspects, including response time, variation of system variables, and instability of operation, are studied for both single- and twin-screw extruders. The effect of a time-dependent variation in the boundary conditions is studied. The coupling due to conduction heat transfer in the screw barrel is found to be very important and is taken into account for single-screw extruders. In the absence of this conjugate coupling, the response time is much shorter. Several other interesting trends are obtained with respect to the dependence of the transient response on the fluid, materials, and operating conditions. Steady state results are obtained at large time. The calculated velocity distributions in the screw channel are compared with experimental results in the literature for steady state flow and good agreement has been obtained. The numerical results show that not all desired operating conditions are feasible. The calculated results for transient transport agree with the few experimental observations available on this system. These results will be useful in the design, control and optimization of polymer extrusion processes.

Modeling and Control of Compression System

2014 ◽  
Vol 693 ◽  
pp. 110-116
Author(s):  
Lukas Smolarik ◽  
Dušan Mudrončík ◽  
Milan Strbo
Keyword(s):  
Dynamic Model ◽  
Mass Flow ◽  
Management Strategy ◽  
Control Valve ◽  
Simulation Models ◽  
Parametric Model ◽  
Modeling And Control ◽  
Physical Systems ◽  
Flow Through ◽  
And Control

Surge is a type of instability, that dramatically affects the operation and life of the turbocharger. There were analyzed the options for the control of surge of which were control designed for surge avoidance (method of minimizing the flow through the control valve). This algorithm is based on the logic of closure control valve at a constant speed regardless of the error. Besides of control were designed surge and control curves. To verify the solution was modeled and implemented nonlinear parametric model with downstream with control valve (Fink model) in Matlab. The simulation models are needed for physical systems, and develop good management strategy. Derivation of the compressor characteristic is presented. Dynamic model also includes two characteristics of valves describing mass flow.

On Linearizing the Steam Mass Flow Relative to the Controller Output

2011 ◽  
Author(s):  
Gerta Zimmer ◽  
Florian C. Hiss
Keyword(s):  
Mass Flow ◽  
Power Plants ◽  
Control Valve ◽  
Process Data ◽  
Steam Power ◽  
Steam Power Plants ◽  
Thermodynamic Conditions ◽  
Flow Through ◽  
Set Up ◽  
Operational Range

In order to develop efficient control and to predict a steam turbine’s power output precisely, it is desirable to have a linear relationship between controller output, RA, and steam mass flow. Unfortunately, steam mass flow through a turbine is not only determined by the control valve stroke but also by the pressure in front of these valves. Even at constant pressure the relation between valve stroke and steam flow through the turbine is extremely non linear. The complexity is increased by the fact that a turbine is generally operated by two or four control valves which do not necessarily work parallel over the complete operational range. Additionally, the pressure in front of the control valve changes with the admitted steam mass flow. A counterbalancing method was developed that allows to include individual process data, such as pressure in front of the valves and at the turbine inlet in dependence of steam mass flow and valve throttle characteristics, as well as process engineering constraints, like valve staggering, for example. The developed method is applicable to new steam power plants as well as to retrofits. With the developed method it is also possible to predict individual valve strokes at valve testing or at deviating exterior conditions. The later feature is extremely useful for retrofit applications. Firstly, the correctness of the implementation with respect to the ‘old’ set-up can be verified, and then, secondly, the characteristics of the retrofitted components and thermodynamic conditions, respectively, can be substituted. The developed method was successfully applied for several power plants. A comparison of predicted data and commissioning data will be provided.

Dynamics Integrated Valve Analysis for Gas Turbine System

2009 ◽  
Author(s):  
Seong G. Kang ◽  
Kune Y. Suh
Keyword(s):  
Gas Turbine ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Power Plants ◽  
Turbine Blades ◽  
Control Valve ◽  
Operating Conditions ◽  
Stop Valve ◽  
Valve Control

A methodology and theory are developed to precisely determine the gas mass flow rate for the design of a gas turbine system manufactured for the operating conditions of nuclear and fossil power plants. From the heat exchanger or boiler to the first assembly of turbine blades, the gas passes by a stop valve, control valves and first nozzle, each device of which is connected with piping. The corresponding gas flow rate can be computed when the thermal and hydraulic conditions are defined at the stop valve, control valve and pipes. Such thermophysical properties as pressure, temperature, enthalpy and velocity specified at the inlet of each device are changed at the outlet of that device due to its structural characteristics. DIVA (Dynamics Integrated Valve Analysis) is written to predict the gas mass flow rate with reference to the Widows’ Creek type control valve.

Transient Behavior of an Ammonia-Based Energy Recovery System

2016 ◽  
Author(s):  
Gabriela Bran-Anleu ◽  
H. Pirouz Kavehpour ◽  
Adrienne S. Lavine
Keyword(s):  
Steady State ◽  
Heat Exchanger ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Energy Recovery ◽  
Flow Reactor ◽  
Ammonia Synthesis ◽  
Transient Behavior ◽  
Steam Temperature

An ammonia thermochemical energy storage system consists of an endothermic reaction that disassociates ammonia into hydrogen using the solar energy, which can be stored for future use. The reverse reaction is carried out in the energy recovery process; the ammonia synthesis reaction is used to heat supercritical steam to temperatures on the order of 650 degrees Celsius as required for a supercritical steam Rankine cycle. The goal of this paper is to investigate the transient response in a synthesis reactor-heat-exchanger. It is desired to predict the time the system takes to reach steady state and the effect a perturbation has on the temperature response of the system. A numerical model has been developed to investigate the transient behavior of an ammonia synthesis reactor-heat exchanger. The model consists of a transient one dimensional concentric tube counter-flow reactor-heat exchanger. The effect of gas mass flow rate and initial gas temperature was investigated. Results show that as gas mass flow rate increases, the time for the outlet steam temperature to reach steady state decreases. For low gas mass flow rates, the required outlet steam temperature is not achieved.

scholarly journals Periodic flow structures in a turbofan fan stage in windmilling

2020 ◽  
pp. 095441002094829
Author(s):  
Nicolás García Rosa ◽  
Adrien Thacker ◽  
Guillaume Dufour
Keyword(s):  
Mass Flow ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Variable Mass ◽  
Flow Coefficient ◽  
Test Bed ◽  
Ambient Conditions ◽  
Low Velocity ◽  
Blade Passing Frequency ◽  
Flow Through

In a fan stage under windmilling conditions, the stator operates under negative incidence, leading to flow separation, which may present an unsteady behaviour due to rotor/stator interactions. An experimental study of the unsteady flow through the fan stage of a bypass turbofan in windmilling is proposed, using hot-wire anemometry. Windmilling conditions are reproduced in a ground engine test bed by blowing a variable mass flow through a bypass turbofan in ambient conditions. Time-averaged profiles of flow coefficient are independent of the mass flow, demonstrating the similarity of velocity triangle. Turbulence intensity profiles reveal that the high levels of turbulence production due to local shear are also independent of the inlet flow. A spectral analysis confirms that the flow is dominated by the blade passing frequency, and that the separated regions downstream of the stator amplify the fluctuations locked to the BPF without adding any new frequency. Phase-locked averaging is used to capture the periodic wakes of the rotor blades at the rotor/stator interface. A spanwise behaviour typical of flows through windmilling fans is evidenced. Through the inner sections of the fan, rotor wakes are thin and weakly turbulent, and the turbulence level remains constant through the stage. The rotor wakes thicken and become more turbulent towards the fan tip, where flow separation occurs. Downstream of the stator, maximum levels of turbulence intensity are measured in the separated flow. Large periodical zones of low velocity and high turbulence intensity are observed in the outer parts of the separated stator wake, confirming the pulsating motion of the stator flow separation, locked at the blade passing frequency. Space-time diagrams show that the flow is chorochronic, and a 2 D non-linear harmonic simulation is able to capture the main interaction modes, however, the stator incidence distribution could be affected by 3 D effects.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

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