Qun Zheng

Numerical Simulation on Turbine Blade Leading-Edge High-Efficiency Film Cooling by the Application of Water Mist

Numerical simulation is performed to explore leading film cooling enhancement by the application of injecting water mist into the air. The accuracy of numerical simulation program for conjugate heat transfer methodology is verified with the C3X gas turbine vanes cooled with leading edge films. The effect of various parameters including mist concentration, mist diameter, different particle wall interactions conditions, and different forces on the improvement of cooling performance is investigated in this paper. It indicates that mist film cooling can decrease the temperature of boundary layer without impact on the temperature of the mainstream and the thickness of boundary layer.

Interaction Between Rotor and Annular Seals: Interlaced and Straight-Through Labyrinth Seals

The rotor dynamics and flow characteristics of a seal-rotor system for a straight-through seal and a corresponding interlaced labyrinth seal were computed. The most significant parameters of the rotor dynamic, such as frequency and amplitude of vibration, were determined by numerical methods. These parameters were then used in an unsteady fluid flow simulation. The numerical results indicated that rotor vibration could increase leakage flow and give rise to an additional aerodynamic force that could act on the rotor. Aerodynamic force produced by the straight-through labyrinth seal tended to reduce the self-excited vibration of the rotor, and this effect became more apparent with an increase in pressure difference, which penetrated the seals. The opposite case resulted in the numerical results of the interlaced labyrinth seal. It was found that the vortex and pressure distribution in the seal cavities was the primary cause of these results. Differences between the two types of labyrinth seals were present...

Investigation on the Highly Loaded Helium Compressor Based on Helium Thermophysical Properties: Part B — The Loss Analysis of Highly Loaded Axial Helium Compressor

Helium compressor is a main component of high temperature gas reactor (HTGR) helium power conversion unit, and its performance has significant effects on the power output and cycle efficiency. In this paper, the flow loss analysis of highly loaded axial helium compressor is carried out using a computational fluid dynamics (CFD) program at both design and off-design point. To understand the loss mechanism of the highly loaded helium compressor, special attention is paid to the tip clearance loss, profile loss and the end wall loss. As is well-known, when increasing the backpressure, the specific power and adverse pressure gradient of general air compressor cascade increase as well. But the specific power and adverse pressure gradient of the highly loaded design helium compressor in this paper will decrease with the backpressure increasing due to the new velocity triangle. So the loss characteristics of the highly loaded helium compressor are different from that of air compressor. From the three-dimensional viscous numerical results, the profile loss is the most important loss source of the highly loaded helium compressor. The proportion of the highly loaded helium compressor profile loss is more than 50%.© 2017 ASME

Numerical investigation on blade leading edge high-efficiency swirl and impingement phase transfer cooling mechanism

ABSTRACT A comparative study of the flow field and heat transfer characteristics between swirl and impingement of mist/air cooling on blade leading edge is carried out to find a better cooling configuration for phase transition cooling. The Eulerian–Lagrangian particle tracking technique is used to investigate mist/air cooling. Comparisons are made between these two cooling forms in such aspects as vortex structure, heat transfer enhancement, pressure loss, and thermal uniformity with and without mist injection. The influences of mist ratio and Reynolds numbers on these parameters are studied in this paper. Results show that heat transfer is enhanced while pressure loss and thermal uniformity are improved by the swirl flow created by vortex impingement. The heat transfer performance increases by about 46.2 and 51.9%, respectively, for impingement and swirl cooling with 8% mist injection, and the pressure loss coefficient increases by 19%. The difference of heat transfer coefficient between swirl and impingement cooling with and without mist injection at high Reynolds number is larger than that at low Reynolds number. In addition, the heat transfer nonuniform coefficient of swirl cooling is about 15% lower than for impingement cooling.

The Comparative Study Between Swirl and Impingement of Mist/Air Cooling on Blade Leading Edge

A comparative study of the flow field and heat transfer characteristics between swirl and impingement of mist/air cooling on blade leading edge is carried out to find better cooling configuration for phase transition cooling. The Eulerian-Lagrangian particle tracking technique is used to investigate the mist/air cooling. Comparisons are made between these two cooling forms in such aspects as vortex structure, heat transfer enhancement, pressure loss, and thermal uniformity with and without mist injection. The influences of mist ratio and Reynolds numbers on these parameters are studied in this paper. Results show that the heat transfer is enhanced, pressure loss and the thermal uniformity is improved by the swirl flow created by vortex impingement. The heat transfer performance increases by about 46.2% and 51.9% for impingement and swirl cooling with 8% mist injection, and the pressure loss coefficient increases by 19%. The difference of heat transfer coefficient between swirl and impingement cooling with and without mist injection at high Reynolds number is larger than that at low Reynolds number. In addition, heat transfer non-uniform coefficient of swirl cooling is about 15% lower than impingement cooling.Copyright

Conjugate heat transfer simulation of turbine blade high efficiency cooling method with mist injection

The idea of utilizing a finely dispersed water-in-air mixture has been proven to be a feasible technique to produce very high cooling rates. The accuracy of numerical simulation program for conjugate heat transfer methodology is verified with the Mark II transonic high pressure turbine stator which is cooled by internal convection through radial round pipes, and different turbulence models and transition models are employed to analyze the influence on results. On the basis of it, the mist cooling is simulated under typical gas turbine operating conditions for internal convective cooling to discuss the improvement of cooling performance. Though the results indicate that mist cooling can decrease the temperature of boundary layer without impact on the temperature of the mainstream and the thickness of boundary layer, the cooling capacity is limited by inadequate evaporation of mist. Considering the distribution of thermal stress and mist evaporation, a compound cooling blade of film cooling with trailing edge ejection is acquired which is modified from the blade of Mark II internal convective cooling; the effects of various parameters including mist concentration and mist diameter on the improvement of cooling performance are investigated, meanwhile the impact of curvature on cooling efficiency and mist trajectory is analyzed finally.

Numerical analysis of flows and aerodynamic forces in honeycomb and labyrinth seals

Rotor dynamics and flow characteristics are computed for a honeycomb seal and a corresponding labyrinth seal. Firstly, rotor dynamic parameters, such as amplitude and frequency of vibration are calculated. Then these parameters are used for unsteady fluid flow computation. Numerical results indicate that the rotor vibration can reduce sealing performance and result in additional aerodynamic force on rotor. Further, the aerodynamic forces tend to reduce the self-excited vibration of rotor, and this effect becomes more apparent with the increase of pressure difference. Vortex in seal cavities is deemed to be the primary cause of the above mentioned results. The differences between the two types of seals are presented in this article. Finally, authors conclude that suitable structure design of honeycomb and labyrinth seals, or their combination can minimize rotor vibration.

Study on the Leakage and Deformation Characteristics of the Finger Seals by Using Numerical Simulation

Depending on the throttling process of finger pad gap and the kinetic energy dissipation within the finger gap, finger seal can reduce the fluid leakage. But the deformation of the finger will increase the finger pad gap, which results in the increasing of overall leakage. To evaluate the performances of the finger seal, we used a two-way fluid-structure interaction method to analyse the seal deformation and flow field through the finger seal simultaneously. The numerical analyses show that a strengthened finger seal or a convergent type pad can be considered to reduce the leakage flow through finger pad gap. Finger pad deformation depends mainly on the pressure difference, but not the finger pad gap. There is a strong vortex in the finger gap, which blocks the fluid leakage. The leakage fluid is divided into many small vortices, the kinetic energy of the leakage fluid is dissipated in such a process and its pressure is decreased. When the finger pad deformed, its high pressure end moves toward the shaft, if the pressure difference increases or the shaft oscillated, this end could touch the shaft surface. The position of the maximum radial movement of finger pad does not coincide with the position of the maximum deformation of finger pad, which means the finger pad will be twisted to some extent rather than simply lift.Copyright

Experimental and numerical investigations of hole injection on the suction side throat of transonic turbine vanes in a cascade with trailing edge injection

Trailing-edge mixing flows associated with coolant injection are complex, in particular at transonic flows, and result in significant aerodynamics losses. The objective of this paper is to evaluate the impacts of hole injection near the suction side throat on shock wave control and aerodynamic losses. A series of tests and calculations on effects of hole injection on the suction-side throat of a high-pressure turbine vane cascade with and without trailing-edge injection were conducted. Wake traverses with a five-hole probe and tests of pressure distributions on the turbine profile were taken for total injection mass flow ratios of 0% and 1.2% under test Mach numbers of 0.7, 0.78, and 0.87. Meantime, numerical predictions are carried out for exit isentropic Mach numbers of 0.7, 0.78, 0.87, and 1.1 and hole-injection mass flow ratios of 0%, 0.17%, 0.3%, and 0.89%. Numerical predictions show a reasonable agreement with the experimental data, and wake total pressure losses and flow angles as well as pressure distributions on the turbine profile were compared to calculations without hole injection, indicating a significant effect of hole injection on the profile wake development and its blockage effect on the shock-wave flow in the vane cascade passage. At subsonic flows, the hole injection on the suction side throat thickens the suction-side boundary layer, and increases the flow mixing, thus causing increased wake losses and flow angles. At transonic flows, while the trailing-edge injection reduces the strength of the shock wave at the trailing-edge pressure side, the hole injection on the suction side throat alters the local pressure fields, and then tends to enhance the shock-wave at the trailing-edge pressure-side; however, it seems to reduce the strength of the shock-wave at the trailing-edge suction side.

Numerical analysis of gas turbine inlet fogging nozzle manifold resistance

Air pressure drop over the nozzle manifolds of inlet fogging system and the flow resistance downstream of the nozzle arrays (manifold) have always been an area of concern and are the object of this paper. Fogging nozzles arrays (involving several hundred nozzles) are mounted on channels and beams, downstream of the inlet filters and affect the pressure drop. The water injection angle, nozzle injection velocities, and the progressive evaporation of the water droplets evaporation all influence the inlet pressure seen at the gas turbine inlet. This paper focuses on a numerical simulation investigation of flow resistance (pressure drop) of inlet fogging systems. In this research effort, the inlet duct is meshed in order to compute the pressure drop over the nozzles frames in fogging and nonfogging conditions. First, the resistance coefficients of an air intake filter are obtained by numerical and experimental methods, and then the coefficients are used for the simulation of the inlet duct by considering the filter as a porous media. Effects of nozzle spread pattern and water injection pattern are then modeled. The results indicate that injection velocity and arrangement of nozzles could have significant effects on the pressure drop and intake distortion, which will affect compressor performance. This paper provides a comprehensive analysis of the pressure drop and evaporation of inlet fogging and will be of value to gas turbine inlet fogging system designers and users.