The Analysis of Leading Edge Deformations on Turbomachine Blades

With recent advancements in the development of material and manufacturing technology, the leading edge geometry of turbomachine blades has attracted widespread attention. “Sharp„ leading edges always have a better aerodynamic performance, though it is prone to deformations easily. Thus, flat plates and real compressor cascades with different leading edge deformations were investigated to study the influence, which is applicable for thin blades at low speeds. Different boundary layer characteristics, including the velocity profile, transition process, and loss, are compared. The results show that there are several kinds of contradictory influence mechanisms and that the final phenomenon is closely related to the condition of the original boundary layer. In low turbulence, with large and laminar separation, the deformations can suppress separation and decrease loss. In high turbulence, with short and transitional separation, deformations can promote the transition process and increase the loss. The sensitivities of different the original leading edge shapes are also compared. This indicates that a good design always has a better robustness at low turbulence values, while it is worse at high turbulence values. The cascade experiment and simulation show that the deformation influence is similar to flat plates and that it is enlarged near the hub, which affects the corner separation

FLOW ANALYSIS OF A SINGLE-STAGE AXIAL COMPRESSOR WITH A SPLITTER ROTOR

ABSTRACT Unsteady and time-averaged flow fields of a single-stage axial compressor with a splitter rotor working in design conditions are simulated and analyzed with 3-D unsteady CFD code. The results show that strong unsteady flow exists in the rotor passage. Splitter reconstructs the pressure distribution in the rotor passage, changes load distribution of the rotor, and controls the flow near the rotor-blade. Splitter affects the unsteady static pressure distribution and fluctuation on principle blade, splitter and stator. INTRODUCTION Application of splitter rotor to axial compressors to raise the stage loading of compressor is one effective method of raising stage loading of fans/compressors. The major design ideology is to add splitter locally on the rear end of the passage between blades, where flows separation most likely happens. The splitter vane can alleviate or erase the flow separation on the backside of the principle blade suction surface, and also can avoid blocking, efficiency decreasing and weight increasing caused by adding full length blades. In the 70s, Dr. Wennerstrom applied the splitter aerodynamic design to avoid large deviation on the outlet of high-loading rotors caused by the stage pressure ratio of more than 3.0, which is based on the traditional design. However the result of the experiment is far from the design value, the reason is that there is a large-scale separation on the blade suction surface. To solve this problem, full 3-D CFD method is required, which is unavailable at that time. Until several decades later, when computer technology and full 3-D numeric simulation programs were developed greatly, by the aid of IHPTET, Textron Lycoming Co. resumed the aerodynamic design with splitter vanes, and great development is obtained. At the end of 90s, based on new design method and full 3-D steady viscous computation, Che

The Evolving Epidemiology of Elderly with Degenerative Valvular Heart Disease: The Guangzhou (China) Heart Study

Aim. The present study was aimed at investigating the prevalence, incidence, progression, and prognosis of degenerative valvular heart disease (DVHD) in permanent residents aged ≥65 years from Guangzhou, China. Methods. This was a prospective study based on community population. Over a 3-year span, we conducted repeated questionnaires, blood tests, and echocardiographic and electrocardiogram examinations (2018) of a random sample of initially 3538 subjects. Results. The prevalence of DVHD increased with age, average values being 30.6%, 49.2%, and 62.9% in 65-74, 75-84, and ≥85 years of age, respectively. The incidence rate was 1.7%/year. Aortic stenosis was the result of DVHD, and the mean transvalvular pressure gradient increased by 5.6 mmHg/year. The increase of mild aortic stenosis was lower than that of more severe disease, showing a nonlinear development of gradient, but with great individual variations. Mortality was significantly increased in the DVHD group (HR=2.49). Risk factors for higher mortality included age (χ2=1.9, P<0.05), renal insufficiency (χ2=12.5, P<0.01), atrial fibrillation (χ2=12.2, P<0.01), mitral regurgitation (χ2=1.8, P<0.05), and tricuspid regurgitation (χ2=6.7, P<0.05) in a DVHD population. Conclusions. DVHD was highly prevalent among residents in southern China. With the progression of the disease, the mean transvalvular pressure gradient accelerated. DVHD was an independent predictor of death, and the mortality was higher in those with older age, renal insufficiency, atrial fibrillation, mitral regurgitation, and tricuspid regurgitation