Teaching Experiences

(1) For Undergraduate -

Principle of Thermal Turbomachinery

Introduction of Computational Fluid Dynamics

(2) For Graduate –

Computational Fluid Dynamics

Turbomachinery Aerodynamics

Research Interests

l          Turbomachinery flows and heat transfer

l          Computational and modeling techniques for cavitation

l          MGT/SOFC hybrid system simulation

l          Seal flows and heat transfer

l          Fluid-structure interaction in labyrinth seal

Research & Engineering Activities Have Contributed to Design of

l          Controlling stage of steam turbine

l          Labyrinth seal, honeycomb seal and brush seal of turbomachinery

l          Low solidity diffuser of centrifugal pump

Professional Societies

Member: American Institute of Aeronautics and Astronautics (AIAA)

        American Society of Mechanical Engineering (ASME)

Introduction of Research Projects

(1) Research and Development of Turbine Blade Optimization Design Technology

The design of a turbomachinery component such as blades is a formidable challenge for designers. It is typically a multiobjective problem (MOP) that simultaneously involves some competing objectives such as maximization of the static pressure rise and minimization of the total pressure loss. An automated optimization design methodology for turbomachinery blades using multiobjective evolutionary algorithms (MOEAs) and Navier-Stokes solver was developed. The multi-branch Tournament selection and Pareto solution conception are used in the presented MOEAs. Elitist method and generation gap are adapted to ensure the optimization performance and decrease the computation expense. The Bezier-curves are utilized to parameterize the designed blade profile and corresponding control points are used as the designed variables. Reynolds-Averaged Navier-Stokes solver is applied to evaluate the aerodynamic performance of the designed candidates. The presented results showed that the development of present optimization design method offers a promising approach to turbomachinery designer to design a better machine.

(2) Leakage Flow, Heat Transfer and Rotordynamic Characteristics of Dynamic Seals in Turbomachinery

Sealing is a critical technology to achieve reliable performance and higher efficiency for turbomachinery. In the modern society, high surface speeds combined with large shaft excursions present major challenges in dynamic seal applications. With the superior sealing and vibration controlling performance over conventional labyrinth seals, the use of honeycomb seals as a replacement of labyrinth seals to eliminate rotordynamic instabilities and control leakage flow in turbomachinery has increased since 1980s. In contrast to the labyrinth seal, the abradable honeycomb liner can mitigate the rotor wear while providing a durable interface that enhances engine efficiency. In spite of the advanced performance of the honeycomb seal, as well as the newly developed hole-pattern seal, detailed researches on the fluid-temperature conjunction, thermal-fluid conjunction and fluid induced excitation phenomenon are still in lack up to now. By using the CFD method, the influence of the geometrical size and working conditions on the leakage, windage heating effect and heat transfer in the stepped labyrinth seal with smooth and honeycomb lands are investigated with the 3D periodic geometrical model. An ideal gas bulk flow analysis method for predicting the rotordynamic characteristics of the honeycomb seal and hole-pattern seal is developed. And the corresponding C++ codes based on this theory are programmed and carefully validated by using the obtained experimental data. With the codes, the influence of the boundary conditions and geometrical sizes of the honeycomb seal and hole-pattern seal on the rotordynamic performance are investigated in detail. The numerical method for predicting the rotordynamic characteristic of the honeycomb seal and hole-pattern seal is developed. By modifying Chochua and Soulas’ numerical method, the circular orbit model is adopted and applied. The accuracy and validity of the presented numerical method and the corresponding solving procedures are demonstrated by using the obtained experimental data. And the insight of the transient flow fields and reaction forces on the rotor is shown and discussed in order to reveal the fluid-induced-excitation phenomenon of the deliberately roughened stator annular seal.

(3) Aerodynamic Performance of Governing Stage of Large Power Steam Turbines

Steam turbine is one of the large power prime motor and widely applied in power plant, petrochemical engineering and so on. The aerodynamic performance and safe reliability of steam turbine is subjected to be emphasized due to increasing strictly environment requirements and manufacturing competitions. Nozzle feed steam and throttling feed steam system are two main structures of large power steam turbines to control their power output at off-designed operating conditions. Nozzle control stage is the critical structure of the nozzle feed steam system and used in large power steam turbines. Aerodynamic performance of the nozzle control stage plays an important role in the operating economical efficiency of steam turbines. Three RANS solution with CFD software is applied to analyze the aerodynamic performance of governing stage at designed and off-designed conditions.

(4) Design of Steam Path, Gland Seals and Valves of Steam Turbines

Leakage flow shows many disadvantages to the aerodynamic performance in turbomachinery, especially the tip clearance leakage flow between the rotor blade and casing endwall. To decrease the leakage flow influence, shrouded rotor blade are designed and utilized in turbomachinery, such as in steam turbines. As to the shrouded rotor blade, the leakage fluid only flows from the leading edge to the trailing edge of the rotor tip. The leakage flow mixes with the wake flow of the rotor blade and influences the inlet condition of the downstream stator stage. To improve the aerodynamic performance of the shrouded turbine stage, the steady and unsteady flow mechanisms interaction with the leakage flow and mainstream is needed to study.

(5) Analysis and Design of Last Stage Blades and Exhaust Hoods of LP Cylinder

Last stage blades(LSBs), being the key element of steam turbines, in many instances dictate the turbine configuration, including the number of LP cylinder. They also to a great degree determinate the turbine’s operating performance. At present, new, longer LSBs for the half rotation speed are mainly developed for large wet steam turbines of nuclear power plants. With the increase the LSB length, not only does the tensile stress caused by centrifugal forces grow, but the danger of water drop erosion increases, too, because of the increase in the tip circumferential speed. In addition, under operating conditions with low steam flow and high back-pressure, longer LSB are also more intensely heated because of friction and fanning in the ambient steam. Design of the roots, shrouds and snubbers of LSB requires special attention to be paid. Blade profile, aerodynamic performance and structure strength validation of the last stage blade is investigated. In addition, steady and unsteady flow fields coupling last stage and exhaust hoods are also needed to study using the parallel high performance computer systems and advanced CFD numerical method.

(6) Steam Cooling Technique in Supercritical and Ultra-Supercritical Steam Turbines

Application of the steam cooling technique is useful to fits use class of components material and expands the design life of ultra-supercritical steam turbine components. Importance of using steam cooling technique for supercritical and ultra-supercritical steam turbine components is analyzed. Design characteristics for cooling structure of nozzle chamber, high pressure rotor, inter-mediate pressure rotor, low pressure rotor and casing of ultra-supercritical steam turbines are investigated together with key technique for cooling structure design of ultra-supercritical steam turbines. The Key techniques included cooling parameter design, finite element analysis of temperature fields and stress fields for components as well as measurement and verification for cooling results.

(7) Flow and Film Cooling of Gas Turbine Blades

Gas turbines are widely applied in aircraft propulsion and power output industrial applications. With the increasing of the inlet temperature, the thermal efficiency and power generation of the gas turbines increase. However, the inlet temperature is limited by the material used in the gas turbines when the development of the high-temperature resistance material is slow. Therefore, there exists a research and development challenge for the cooling technology of the turbine blade. The gas leakage through the gap results in the high heat transfer coefficient on the blade tip, and the heat transfer rates at the blade tip can be one of the highest on the entire blade surface. The blade failures caused by the tip oxidation remain as a challenge problem. Thus, based on the related experimental data, the numerical simulation method is applied to study the characteristics of the tip leakage flow and heat transfer in the moving blade of modern gas turbine. In addition, the effects of the film hole position and the blowing ratio on the film cooling effectiveness in the squealer tip are analyzed.

(8) Simulation Model Development of Micro Gas Turbine/Solid Oxide Fuel Cell Hybrid System

The hybrid Micro Gas Turbine (MGT) and Solid Oxide fuel cell (SOFC) system is a promising concept in the future power generation for its high-performance and low-emission. The dynamic model for the hybrid system of integrated SOFC and recuperative GT with air reheating component is investigated and presented. A dynamic model is put forward based on the conservation equations of mass, energy and force through the whole plant, with specific source terms in different types of components. The SOFC is modeled on the basis of the Exponential Decay function and the Exponential Associate function, which describe the characteristics of the parameters distribution within the SOFC. A cubic curve is employed to denote the compressor pressure characteristics. In the turbine model, the relation between the work done and the inlet condition of turbine is determined according to the turbine nozzle work characteristics. Cycle simulation and analysis for two kinds of SOFC/GT hybrid systems are conducted with the help of the simulation tool Aspen Custom Modeler. Two cycle schemes of recuperative heat exchanger (RHE) and exhaust gas recirculated (EGR) are described according to the air reheating method. Some promising results of the MGT/SOFC hybrid system are presented.

(9) Numerical Method Development of Cavitation Simulation

Cavitation is a widely existing hydrodynamic phenomenon that has received much attention over the past decades. Cavitation physics plays an important role in the design and operation of many liquid handling turbomachines and devices. A new numerical algorithm for attached cavitation flows was developed. A cavitation model was implemented in a viscous Navier-Stokes solver. The liquid-vapor interface was assumed as a free surface boundary of the computation domain. Its shape was determined with an iterative procedure to match the cavity surface to a constant pressure boundary. The pressure distribution, as well as its gradient along the wall, was taken into account in updating the cavity shape iteratively. The obtained results are reasonable and the iterative procedure of cavity shape updating is quite stable. The superiority of the developed cavitation model and algorithm is demonstrated according to some numerical simulation results.