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We investigate the behaviour of a dynamic fluid-structure interaction model of a chorded polyurethane mitral valve prosthesis, focusing on the effects on valve dynamics of including descriptions of the bending stiffnesses of the valve leaflets and artificial chordae tendineae. Each of the chordae is attached at one end to the valve annulus and at the other to one of two chordal attachment points. These attachment points correspond to the positions where the chords of the real prosthesis would attach to the left-ventricular wall, although in the present study, these attachment points are kept fixed in space to facilitate comparison between our simulations and earlier results obtained from an experimental test rig. In our simulations, a time-dependent pressure difference derived from experimental measurements drives flow through the model valve during diastole and provides a realistic pressure load during systole. In previous modelling studies of this valve prosthesis, the valve presents an unrealistically large orifice at beginning of diastole and does not close completely at the end of diastole. We show that including a description of the chordal bending stiffness enables the model valve to close properly at the end of the diastolic phase of the cardiac cycle. Valve over-opening is eliminated only by incorporating a description of the bending stiffnesses of the valve leaflets into the model. Thus, bending stiffness plays a significant role in the dynamic behaviour of the polyurethane mitral valve prosthesis.

SUMMARYAn Immersed Boundary fluid-structure interaction model is developed to investigate the dynamic behaviour of a prosthetic chorded mitral valve (MV) inside the left ventricle (LV). In order to simulate more realistic physiological flow conditions, in vivo magnetic resonance images of the LV are used to determine the anatomical structure and the motion of the LV. The LV geometry and its motion are incorporated into the dynamic MV model. This model allows us to investigate the influences of the flow vortex generated by the LV motion on the MV dynamics, as well as the impact of the motion of the chordae attachment points (CAPs). Results are compared with two other cases: (i) an LV model with no prescribed motion of the CAPs, (ii) a Tube model in which the LV is replaced by a tube, although the motion of the chordae is incorporated. These special cases enable the influence of the chordae motion and the vortex on the behaviour of the MV to be analysed independently. It is found that when the MV is placed inside a dynamic LV, the chordae and the valve stretch are significantly increased in the commissural region, and the flow field is strongly asymmetric, with a clockwise single vortex appearing after the early rapid filling phase of the diastole. Given that we impose a flow rate boundary condition, the reverse pressure gradient cannot be established and, hence, the valve does not close properly. Clearly, the presence of the flow vortex alone is not strong enough to aid the valve closure.

BackgroundTranscatheter mitral valve-in-valve (TMVIV) procedure with aortic transcatheter heart valves has recently become a less invasive alternative for patients with mitral bioprosthetic dysfunction. This study reports the initial experience of TMVIV implantation using the J-Valve System (JieCheng Medical Technology Corporation Ltd., Suzhou, China).MethodsA retrospective observational multicenter study was conducted to evaluate the short-term outcomes of TMVIV. In total, 26 consecutive patients with symptomatic bioprosthetic failure at eight hospitals underwent TMVIV using the J-Valve System between May 2019 and June 2021. Procedural results and clinical outcomes were analyzed using the Mitral Valve Academic Research Consortium criteria.ResultsThe mean age was 75.3 ± 7.1 years and 69.2% of patients were female. The mean Society of Thoracic Surgeons Predicted Risk of Mortality score was 12.3 ± 8.3%. The technical success rate was 96.2%. Nine of the 26 patients (34.6%) were implanted with a J-Valve of a size equal to the internal diameters of the deteriorated prostheses. At the 30-day and 1-year follow-ups, all-cause mortality was 3.8 and 16.0% and the stroke rates were 0 and 12.0%, respectively. Device-related mortality was 0% and the mean mitral valve gradient was 6.4 ± 2.7 mm Hg. No patient experienced device embolization, left ventricular outflow tract obstruction, or mitral valve reintervention. Postprocedural mitral regurgitation was none or trace in all the patients. All the patients were in the New York Heart Association (NYHA) class ≤ II at the last follow-up.Conclusion:Transcatheter implantation of the J-Valve System in high-risk patients with mitral bioprosthetic dysfunction was found to be a reasonable alternative and associated with good short-term outcomes.

The aerodynamic and mechanical performance of the last stage was numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solution and Finite Element Analysis (FEA) coupled with the one-way and two-way fluid-structure interaction models in this work. The part-span damping snubber and tip damping shroud of the rotor blade and aerodynamic pressure on rotor blade mechanical performance was considered in the one-way model. The two-way fluid-structure interaction model coupled with the mesh deformation technology was conducted to analyze the aerodynamic and mechanical performance of the last stage rotor blade. One-way fluid-structure interaction model numerical results show that the location of nodal maximum displacement moves from leading edge of 85% blade span to the trailing edge of 85% blade span. The position of nodal maximum Von Mises stress is still located at the first tooth upper surface near the leading edge at the blade root of pressure side. The two-way fluid-structure interaction model results show that the variation of static pressure distribution on long blade surface is mostly concentrated at upper region, absolute outflow angle of long blade between the 40% span and 95% span reduces, the location of nodal maximum displacement appears at the trailing edge of 85% blade span. Furthermore, the position of nodal maximum Von Mises stress remains the same and the value decreases compared to the oneway fluid-structure model results.

The design of a low reaction turbine blade profiles was carried out to improve the steam flow efficiency. The blade profiles geometry design for both the stationary and moving blades and reprofiling of them are done using Vista ATBlade, according to the aerodynamic analysis results from the cascade analysis code MISES. The original stator profile is aft-loaded, and the new one present in this paper is highly-aft-loaded (HAL) to depress the development of secondary flow further, while maintaining even lower profile loss and wider incidence angle tolerance. The newly designed moving blade is more robust compared with the original one, thus it has larger aspect ratio under the same blade section average stress level, and with better incidence tolerant capability as well. The planar cascade air tests were first carried out to verify the stator profile loss improvement, with a decrease of energy loss coefficient of almost 0.8% obtained under the Reynolds number of about 1e6. Then the annular cascade air tests with fully 360 degrees stator blades installed were conducted to validate the reduction of endwall loss and the profile loss as well, and to measure the mass flow capability (real mass flow/ideal mass flow). Finally, two three-stage tests for the original blades and the new one were developed to verify the improvement under real multi-stages flow conditions. All the stages for both tests are designed with the hub reaction of about 15%, without interstage swirl, in the design condition. The flow probes at upstream of first stage stator and downstream of last stage moving blade, the hydraulic dynamometer and the flowmeter are used to test the overall efficiency. Three traverse planes are located at the upstream, middle and downstream of the second stage to measure the flow properties using five hole pneumatic probes. The test results showed a increase of overall efficiency of about 1.5%. The CFD simulations showed very good agreement of mass flow capability with the tests, for both the stator annular and multi-stage tests. The application of the newly designed blade profiles in SanHe subcritical reheat 300MW steam turbine (16.7MPa/537°C/537°C) retrofit gives the final proof of the efficiency improvement. The measured efficiency showed remarkable performance, with an increase of efficiency of 1.5%–2.2% for both the HP and IP cylinder.

A well-designed exhaust hood of large steam turbines would recover some kinetic energy from the flow between the last stage blades and condenser, which improves the efficiency of the cylinder. The internal flow field of the exhaust hood was firstly numerical investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions based on the ANSYS-CFX. Then, the effects of the dimensions of the cylinder, bearing cone, diffuser guide, and diffuser ribs on the static pressure recovery performance of the exhaust hood were numerically conducted. The numerical results show that the cylinder length has significantly impact on the static pressure recovery coefficient of the exhaust hood by comparison of the cylinder section area at the fixed bearing cone and diffuser size. The bearing cone and diffuser were optimized to improve the aerodynamic performance of the exhaust hood. The rotationally symmetrical and enlarged diffusers show the different static pressure recovery performance of the exhaust hood. The optimized exhaust hood shows the improved aerodynamic performance by comparison of the initial design. The detailed flow pattern of the initial and optimized exhaust hood is also illustrated and discussed. This paper explicitly shows the interaction, and offers a good strategy for optimization, which has not been thoroughly discussed.

High performance of the last stage long blade plays an important role on the aerodynamic performance of low pressure cylinder for steam turbines. Aerodynamic optimization design of the last stage long blade for the maximization total-total isentropic efficiency with constraints of mass flow rate and leaving velocity using self-adaptive differential evolution algorithm is presented in this work. The aerodynamic performance of last stage is evaluated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) computations. Six two-dimensional airfoils along the span and three controlling points for the radial foil of blade using B-Spline functions are used to parameterize the three-dimensional profiles of the stator and rotor blade of the last stage, respectively. Self-adaptive differential evolution algorithms is developed to optimize the maximization total-total isentropic efficiency of last stage. The results show that the total-total isentropic efficiency of the optimized last stage is higher 1.68% than that of the referenced design. Furthermore, the aerodynamic performance of the five stages low pressure cylinder with three extractions coupled with the optimized last stage and referenced design is analyzed and compared. The detailed flow field and aerodynamic parameters of the optimized last stage are also illustrated.