Optimum Tilt Angle of Flow Guide in Steam Turbine Exhaust Hood Considering the Effect of Last Stage Flow Field

Abstract Heat transfer and vacuum in condenser are influenced by the aerodynamic performance of steam tur- bine exhaust hood. The current research on exhaust hood is mainly focused on analyzing flow loss and optimal design of its structure without consideration of the wet steam condensing flow and the exhaust hood coupled with the front and rear parts. To better understand the aerodynamic performance influenced by the tilt angle of flow guide inside a diffuser, taking a 600 MW steam turbine as an example, a numerical simulator CFX is adopted to solve compressible three-dimensional （3D） Reynolds time-aver- aged N-S equations and standard k-e turbulence model. And the exhaust hood flow field influenced by different tilt angles of flow guide is investigated with consideration of the wet steam condensing flow and the exhaust hood coupled with the last stage blades and the condenser throat. The result shows that the total pressure loss coefficient and the static pressure recovery coefficient of exhaust hood change regularly and monotonously with the gradual increase of tilt angle of flow guide. When the tilt angle of flow guide is within the range of 30~ to 40~, the static pressure recovery coefficient is in the range of 15.27% to 17.03% and the total pressure loss coefficient drops to approximately 51%, the aerodynamic performance of exhaust hood is significantly improved. And the effectiveenthalpy drop in steam turbine increases by 0.228% to 0.274%. It is feasible to obtain a reasonable title angle of flow guide by the method of coupling the last stage and the condenser throat to exhaust hood in combination of the wet steam model, which provides a practical guidance to flow guide transformation and optimal design in exhaust hood.

Effects of two different glycoprotein platelet Ⅱb/Ⅲa inhibitors and the clinical endpoints in patients with intracranial Pipeline flow diverter implant

Objective:To compare the antiplatelet effect and major adverse cerebrovascular events of Pipeline for intracranial aneurysms using glycoproteinⅡb/Ⅲa antagonists(GPI)eptifibatide and tirofiban.Methods:Retrospective analysis of relevant data of patients using GPIs combined with oral antiplatelet therapy in Nanfang Hospital of Southern Medical University from December 2017 to December 2019.The study was approved by the ethics Committee of Nanfang Hospital of Southern Medical University.According to the random use of GPIs drugs,they were assigned to the eptifibatide group and tirofiban group.Basic data,platelet inhibition rates at baseline,24 h and 72 h after administration,short-term major adverse cerebrovascular events,and bleeding complications were compared between the two groups.Results:A total of 47 patients were included in this study,including 24 patients in eptifibatide group and 23 patients in tirofiban group.There was no significant difference in average age(53.75 vs.53.91 years)and body mass index(BMI)(24.39 vs.22.73 kg/m2)between eptifibatide group and tirofiban group.There was no significant difference in coagulation factor function(R),fibrinogen function(K),fibrinolysis function(EPL),comprehensive coagulation index(Cl),arachidonic acid pathway inhibition rate(AA%)and adenosine diphosphate inhibition rate(ADP%).However,the baseline level of residual platelet function MA(ADP)in eptifibatide group was significantly higher than that in tirofiban group(50.79 vs.35.29 mm,P=0.0026).There was a statistical difference in the platelet aggregation function MA(65.38 vs.62.54 mm,p=0.0442),the rate of spontaneous hemorrhagic stroke(4.3%vs.0%)and the rate of asymptomatic minor bleeding(26.08%vs.4.1%)in the two groups(P<0.05).Conclusion:Both eptifibatide and tirofiban can effectively inhibit platelets,but the effect of etifeptide is better than that of tirofiban in preventing intracranial microhemorrhage and asymptomatic cerebral infarction.

Transient simulation of a pump-turbine with misaligned guide vanes during turbine model start-up

Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement by using misaligned guide vane were verified by model test and simulation. The transient flow calculations were used to clarify the variations of pressure pulse and internal flow behavior in the entire flow passage. The use of misaligned guide vanes can eliminate the S-curve characteristics of a pump-turbine, and can significantly increase the pressure pulse amplitude in the entire flow passage and the runner radial forces during start-up. The MGV only decreased the pulse amplitude on the guide vane suction side when the rotating speed was less than 50% rated speed. The hydraulic reason is that the MGV dramatically changed the flow patterns inside the entire flow passage, and destroyed the symmetry of the flow distribution inside the guide vane and runner.

Effect of structure parameters of the flow guide vane on cold flow characteristics in trapped vortex combustor

The cold flow characteristics are investigated to show the effect of the structural parameters of the flow guide vane on the trapped vortex combustor（TVC）. The results show that the structural parameters have significant effects on the TVC. As a/ H increases, the total pressure loss, the wall shear stress at the bottom of the cavity and the turbulent intensity in the main combustion zone increase. b/ B does not have a significant effect on the cavity flow structure and the total pressure loss, and the wall shear stress at the bottom of the cavity increases as b/ B increases. There is no significant increase of the turbulent intensity with the increase of b/ B. The increase of c/ L has little effect on the total pressure loss, and it is not conducive to a stable combustion. As c/ L increases, the wall shear stress at the bottom of the cavity decreases. When a/ H= 0.4, b/ B= 0.4, c/ L= 0.1, a desirable dual-vortex structure is formed with an acceptable pressure loss to achieve a stable combustion. Moreover, to ascertain that the flame is stable for different values of Vm a with the optimal structural parameters, the effect of Vm a on the flow field is discussed. Results suggest that the dual-vortex structure has no relationship with the increase of Vm a. Furthermore, an unsteady simulation is conducted to show the generation and the development of the dual-vortex.

3-D NUMERICAL SIMULATIONS OF FLOW LOSS IN HELICAL CHANNEL

The flow loss of a helical channel Magnetohydrodynamic （MHD） thruster without MHD effect was numerically studied with 3-D simulations, and a flow loss coefficient （ was defined to quantify the flow loss and its influencing factors were studied. The results show that （ decreases in a first-order exponential manner with the pitch of a helical wall and the Reynolds number, and it declines slowly when t / T 〉 0.2 and Re 〉 10^5, a flow guide makes the flow more smooth and uniform, especially in the flow guide and helical wall sub-regions and thus reduces the flow loss greatly, by about 30% with the averaged value of （ from 0.0385 to 0.027, a rectifier weakens the helical flow and strengthens the axial one in the rectifier and outlet sub-regions, thus reduces the rotational kinetic pressure with the averaged value of ξ declining about 4% from 0.0385 to 0.037, and ξ decreases with a rectifier＇s axial length when Re 〉 10^5 .