Numerical Simulation Of Turbulent Flow Behind A Butterfly Valve Placed In A Dual-elbow Channel And Its Experimental Analysis

Because of its simple structure, convenient operation and otherreasons, butterfly valve is widely used in the industrial fields such aspower engineering, municipal water supply, chemical industry,shipbuilding and so on as a flow control®ulating device. However, inthe process of butterfly valve-disc angle regulation to implement flowcontrol, flow separation often occurs in the valve-disc downstream, whicheasily induces noise radiation, structural vibration and other unfavorablephenomena. Flow separation phenomena in the butterfly valve arranged inthe long straight channel have been paid much widely attention and givenenough research. However, in some special situations, butterfly valve andelbow channel often need a nearby coordinate application because of spaceconstraint and other reasons, which brings more complex flow phenomenainside the channel; on the other hand, this will bring many disadvantagesto the valve stem and other driving components. Therefore, it is verynecessary to carry out some research and flow field analysis to obtainrelevant flow and mechanical properties.This paper employs computational fluid dynamics (CFD) to do someresearch, combining with pneumatic model experiment and taking theexhaust valve of the middle and low pressure cylinder in some certain power plant cogeneration steam turbine as the prototype and usingproportional scaling model. Specifically, it carries out the flow andvibration characteristics analysis for complex flow in the dual-elbowchannel behind butterfly valve. The practical engineering significance ofthis study is to help user understand the internal complex flow field andvibration characteristic, providing reference for valve actuator choice, andtheoretical basis for the follow-up improvement measures. Therefore, themain content of this study consists of two following parts:(1) Numerical simulation on the flow field, mainly including threeparts. First, the preparatory exploratory work, including simplified andoriginal model comparison and butterfly valve with straight pipe systemand dual-elbow pipe without butterfly valve system flow field analysis.Secondly, it is simulation study on the influence of inlet Reynolds number.Thirdly, it is simulation study on the influence of valve-disc inclinationangle.(2)Aerodynamic model experiment analyses are carried out and itmainly includes the torque, velocity field and pressure fluctuation test toverify the mechanical properties, flow time average and fluctuatingcharacteristics.The main results and conclusions are listed below:(1)SST turbulence model is the most suitable model for flow simulation compared with other two models; simplified model can be i-n high fidelity to simulate the complex flow field compared with th-e two model; Butterfly valve with straight pipe system and dual-elb-ow pipe without butterfly valve system can help to understand complex flow, including the flow separation, second flow, collision flow and shear flow.(2) Inlet Reynolds number have quantitative influence on the flow field.When the inlet Reynolds number ranges from5.8104to2.4105of45°inclination angle, flow field distribution does not change greatly; forceFx andFy and torque on the valve disc， dimensionless pressure loss between the inlet and outlet，the maximum kinetic energy in the mid-planeare the quadratic functions of the inlet Reynolds number; Energyconsuming parameter is the cubic function of inlet Reynolds number.Minimum dimensionless pressure parameter on the valve disc reduces;inlet Ma proportionally increases while the maximum Ma number showsnonlinear increase, where the ratio increases; the stagnation point remainsunchanged (x=-0.21d)while the first separation zone and the secondseparate region decreases gradually.(3) Valve disc inclination angle can qualitatively affect the flow field,which can be explained by the flow separation, secondary flow and flowshear&collision theory. When the valve-disc angle moved from-45°to45°through0°, absolute value of the torque and forceFx andFy on thevalve disc，energy consuming parameter，dimensionless pressure lossbetween inlet and outlet，the maximum turbulent kinetic energy in themid-plane first decreases and then increases, while the flow rate parameterfirst increases and then decreases, and have the peak value around0°.Onthe other hand, these variables changed rapidly when the absolute value ofthe inclination changed from30°to45°.When comparing two cases withthe same inclination angle while the opposite turning direction, flowparameter, dimensionless pressure loss between inlet and outlet and themaximum Ma number in the mid-plane, the case with negative angle issmaller than that with positive angle, where it is opposite for the energyconsuming parameter. The maximum dimensionless pressure parameter isone and located in the upstream face. The front stagnation point movestoward the edge and arrives at leading edge of the valve disc and thenmove toward the center of the valve disc face.(4) Pneumatic experiment for this model reveals that the numericalcalculation have a higher consistency value with the test for butterflyvalve-disc torque measurement of five inlet Reynolds number in45°degree; CFD velocity contour also agrees with the PIV test results in -30°,-15°and0°when the mass flow rate in the model inlet is0.0926kg/s;Spectrum analysis by CFD can obtain the characteristics frequency rangesfrom30Hz to100Hz for pressure pulsation for-15°and-30°inclinationangel when the mass flow is0.1701kg/s, which agrees with theexperimental measurement in general.