Zhenping Feng

Investigations on the Rotordynamic Characteristics of a Hole-Pattern Seal Using Transient CFD and Periodic Circular Orbit Model

Numerical investigations on the rotordynamic characteristics of a typical hole-pattern seal using transient three-dimensional Reynolds-averaged Navier–Stokes (RANS) solution and the periodic circular orbit model were conducted in this work. The unsteady solutions combined with mesh deformation method were utilized to solve the threedimensional RANS equations and obtain the transient reaction forces on a typical holepattern seal rotor at five different excitation frequencies. The relation between the periodic reaction forces and frequency dependent rotordynamic coefficients of the holepattern seal was obtained by considering the rotor with a periodic circular orbit (including forward orbit and backward orbit) of the seal center. The rotordynamic coefficients of the hole-pattern seal were then solved based on the obtained unsteady reaction forces and presented numerical method. Compared with the experimental data, the predicted rotordynamic coefficients of the hole-pattern seal are more agreeable with the experiment than that of the ISO-temperature (ISOT) bulk flow analysis and numerical approach with one-direction-shaking model. Furthermore, the unsteady leakage flow characteristics in the hole-pattern seal were also illustrated and discussed in detail. DOI: 10.1115/1.4003403

2D Viscous Aerodynamic Shape Design Optimization for Turbine Blades Based on Adjoint Method

This paper presents an adjoint optimization technique and its application to the design of a transonic turbine cascade. Capable of a quick and exact sensitivity analysis and using little computational resources, the adjoint method has been a focus of research in aerodynamic shape design optimization. The goal of this work is to extend the adjoint method into turbomachinery design applications for viscous and compressible flow, and to further improve the aerodynamic performance. In the work, the minimization of the entropy generation rate with the mass flow rate constraint was considered as the cost function of the optimization, and was applied in the direct design process. The adjoint boundary conditions of the corresponding cost function were derived in detail, using the nonslip boundary condition on the blade wall, while the flow viscous effect on the cascade inlet and outlet was neglected. Numerical techniques used in Computational Fluid Dynamics (CFD) were employed to solve the adjoint linear partial difference equations. With the solved adjoint variables, the final expression of the cost function gradient with respect to the design variables was formulated. Combined with quasi-Newton algorithm, an aerodynamic design approach based on the adjoint method for turbine blades was presented, which was independent of the Navier–Stokes solver being used. Finally, to validate the present optimization algorithm, the aerodynamic design cases of a transonic turbine blade with and without mass flow rate restriction were performed and analyzed.

Investigations on the Discharge and Total Temperature Increase Characteristics of the Labyrinth Seals With Honeycomb and Smooth Lands

The viscous work generated by the rotating components of a seal not only represents a direct loss of power but also causes an increase in the total temperature of fluid (windage effect). In order to study the discharge and total temperature increase characteristics of the stepped labyrinth seals with smooth and honeycomb lands, 3D Reynolds-averaged Navier‐Stokes solutions from CFX is used in this work. At first, the influences of the inlet preswirl, leakage flow rate, and rotational speed on the total temperature increase in the convergent and divergent stepped labyrinth seals with smooth and honeycomb lands are conducted. The obtained 3D numerical results are well in agreement with the referenced experimental data. It shows that the utilized numerical approach has sufficient precision to predict the total temperature increase in seals. Then, a range of pressure ratios and four sizes of sealing clearance are performed to investigate the effects of sealing clearances and pressure ratio impact on the discharge and total temperature increase of the stepped labyrinth seals with honeycomb and smooth liners. DOI: 10.1115/1.3068320 Nowadays, the increasing demands of performance and fuel efficiencies for the gas turbine engine lead to an increase in core flow temperature. In order to protect the turbine airfoil from thermal stress fields created by exposure to the combustion gases, more and more advanced cooling technologies are introduced by the researchers. However, achievements of enhancing cooling for the gas turbine engine will encounter the windage heating effect in seals. In the internal cooling air system, seals serve the purpose of metering the cooling air to prevent hot air ingress. The viscous work generated by the rotating components, the so-called windage heating effect, will induce an increase in the total temperature of the fluid. It degrades the cooling quality and in turn necessitates increasing the quantities of cooling flow extracted from the main gas path. Neglect of such effect will decrease the lifetime of blades working in a high temperature environment. Second, the cooling air is contaminated by the labyrinth seal leakage flow and then passes into the blades or interstage cavities for the purpose of cooling. The heat transfer characteristics in the next gas path are directly affected by the former outlet temperature and exit swirl. As a result, cooling air temperature is the most important information for a gas turbine designer or researcher to evaluate the cooling quality of the components and quantity of the cooling flow. Hence it is crucial to study the total temperature increase characteristic in the seal. There are many factors that can affect windage effect. One of these factors is the inlet preswirl. The positive preswirl will decrease the total temperature difference between seal inlet and outlet 1‐3. Another factor is the swirl development in the seal chamber. Moreover, for interstage seals, the exit swirl can change the incidence angle of the main flow into the downstream blades,

Effects of Coating Thickness, Test Temperature, and Coating Hardness on the Erosion Resistance of Steam Turbine Blades

This paper experimentally examines the influence of coating thickness, test temperature, coating hardness, and defects on the erosion resistance of boride coatings, ion plating CrN coatings, and thermal spraying coatings. The results demonstrate that the erosion rate of coating can be reduced effectively by improving coating hardness and thickness with the absence of the cracks of coating during the coating process. In comparison with thermal spraying coatings, boride coatings and ion plating CrN coatings are more suitable for protecting steam turbine blades from solid particle erosion due to higher erosion resistance. However, blades cannot be protected effectively when coating is thinner than a critical value θ crit , Based on our results, it is recommended that the protective coating for the steam turbine blade should be thicker than 0.02 mm. In addition, the effect of temperature on erosion resistance of the coating is strongly dependent on the properties of transition layer between coating and substrate material. For the coating without pinholes or pores in the transition layer, the variation in erosion rate with temperature is consistent with that of uncoated substrate material. However, the erosion rate of coating descends with the elevation of test temperature when a lot of pinholes or pores are produced in the transition layer.

Effects of Intersection Angles on Flow and Heat Transfer in Corrugated-Undulated Channels With Sinusoidal Waves

This paper reported three-dimensional numerical simulations of the steady laminar flow and heat transfer in corrugated-undulated channels with sinusoidal waves, aiming to investigate the effects of intersection angles (θ) between corrugated and undulated plate and Reynolds number (Re) on the flow and heat transfer. The simulations are conducted by using multi-channel computational domain for three different geometries. The code is validated against experimental results and then data for Nusselt number (Nu) and friction factor (f) are presented in a Re range of 100-1500, and intersection angle range of 30-150 deg. The simulation confirms the changes of Nuu (averaged over undulated plate) and Nuc (averaged over corrugated plate) with 0 representing different characteristics. As θ increases, Nu (Nuu or Nuc) is about 2-16 times higher for the corrugated-undulated configurations CP-UH1 and CP-UP1 and the concomitant f is about 4-100 higher, when compared to a straight channel having square cross section. The minimum of local Nu ( Nuu or Nuc ) is situated at the four contact points where the top plate touches the bottom one, and the high Nu is located upstream of the crest of the conjugate duct. Performance evaluation for the CP-UH1 channel shows that the goodness factors (G) are larger than 1 with the straight channel having a square cross section as a reference, and the 30 deg geometry channel has optimal flow area goodness.

Numerical Study of Swirl Cooling in a Turbine Blade Leading-Edge Model

In this paper, a numerical simulation is conducted to predict the swirl cooling performance of an internal leading-edge cooling passage model for a gas turbine blade. The swirling cooling performance and its effectiveness are investigated in the case of two rectangular section inlets that cause flow to impinge tangentially on the internal surface of the circular cooling passage. Parametric analysis on the local and average flows and heat transfers are performed at various Reynolds numbers, as well as the ratio of swirl chamber radius to jet slot height for a constant ratio of swirl chamber radius to jet nozzle length and constant jet nozzle area, respectively. The results indicate that the position of the swirl flow center is changing along the axial of the swirl chamber, and the swirl flow center of one constant axial section is not uniform as well in different ratios of swirl chamber radius to jet slot height. The larger ratio of swirl chamber radius to jet slot height and the higher Reynolds number are...

Effects of aerodynamic parameters on steam vortex cooling behavior for gas turbine blade leading edge

Three-dimensional Reynolds-averaged Navier–Stokes equations are applied to further explore steam vortex cooling mechanism in gas turbine blade leading edge. Grid independence analysis and turbulence model validation are carried out to determine the proper grid dimension and turbulence model for simulations. Influences of Reynolds number and temperature ratio on steam vortex cooling flow and heat transfer behavior for the blade leading edge are investigated. Heat transfer and friction correlations for steam vortex cooling are achieved on the basis of numerical data. Results show that radial convection is generated due to violent rotational motion and uneven density distribution, contributing to heat transfer enhancement. For the sake of increasing steam velocity, the obvious increase in heat transfer intensity and decrease in friction coefficient are observed with the increasing Reynolds number. When the temperature ratio increases, the heat transfer intensity decreases slightly and the friction coefficient decreases significantly. The thermal performance increases with the increasing Reynolds number and the decreasing temperature ratio. Compared with calculating results, the heat transfer and friction correlations can predict steam vortex cooling characteristics accurately.

Effects of Pressure Ratio and Rotational Speed on Leakage Flow and Cavity Pressure in the Staggered Labyrinth Seal

Effects of pressure ratio and rotational speed on the leakage flow and cavity pressure characteristics of the rotating staggered labyrinth seal were investigated by means of experimental measurements and numerical simulations. The rotating seal test rig with turbine flowmeter and pressure measuring instruments was utilized to investigate the leakage flow of the staggered labyrinth seal at eight pressure ratios and five rotational speeds. The repeatability of the experimental data was demonstrated by three times measurements at different pressure ratios and fixed rotational speed. The three-dimensional Reynolds-averaged Navier–Stokes equations and standard k-e turbulent model were also applied to study the leakage flow characteristics of the staggered labyrinth seal at the experimental conditions. The validation of the numerical approach was verified through comparison of the experimental data. The detailed flow field in the staggered labyrinth seal was illustrated according to the numerical simulations. The experimental and numerical results show that the leakage flow coefficient increases with increasing pressure ratio at the fixed rotational speed and is more sensitive to the smaller pressure ratio. The influence of rotational speed on the leakage flow coefficient is not obvious in the present rotational speed limitations. The cavity pressure coefficient in the staggered labyrinth seal decreases and is significantly influenced by the cavity structure along the flow direction.

Effects of Inlet Preswirl and Cell Diameter and Depth on Honeycomb Seal Characteristics

Three-dimensional Reynolds-averaged Navier–Stokes solutions are employed to investigate the discharge and total temperature increase characteristics of the stepped labyrinth seal with honeycomb land. First, the relations between the windage heating number and the circumferential Mach number at different Reynolds numbers for different honeycomb seals are calculated and compared with the experimental data. The obtained numerical results show that the present three-dimensional periodic model can properly predict the total temperature increase in honeycomb seals. Then, a range of pressure ratios, three inlet preswirl ratios, four sizes of honeycomb cell diameter, and nine sizes of cell depth are selected to investigate the influence of inlet preswirl ratios and honeycomb geometry sizes on the discharge and total temperature increase characteristics of the stepped labyrinth seal. It shows that the leakage rate increases with the increase in cell diameter, and the cell depth has a strong influence on the discharge behavior. However, the influence of the inlet preswirl on the leakage rate is found to be little in the present study. For the total temperature increase characteristic, the inlet preswirl ratio and pressure ratio have more pronounced influence than those of cell depth and diameter. Furthermore, the relations between the leakage rate and cell depth and diameter, as well as the relations between the windage heating power and cell depth and diameter, are not monotonic functions if the pressure ratio is kept constant. DOI: 10.1115/1.4001296

Aerodynamic Design and Numerical Investigation on Overall Performance of a Microradial Turbine With Millimeter-Scale

For millimeter-scale microturbines, the principal challenge is to achieve a design scheme to meet the aerothermodynamics, geometry restriction, structural strength, and component functionality requirements while in consideration of the applicable materials, realizable manufacturing, and installation technology. This paper mainly presents numerical investigations on the aerothermodynamic design, geometrical design, and overall performance prediction of a millimeter-scale radial turbine with a rotor diameter of 10 mm. Four kinds of turbine rotor profiles were designed, and they were compared with one another in order to select the suitable profile for the microradial turbine. The leaving velocity loss in microgas turbines was found to be a large source of inefficiency. The approach of refining the geometric structure of rotor blades and the profile of diffuser were adopted to reduce the exit Mach number, thus improving the total-static efficiency. Different from general gas turbines, microgas turbines are operated in low Reynolds numbers (10 4 ―10 5 ), which has significant effect on flow separation, heat transfer, and laminar to turbulent flow transition. Based on the selected rotor profile, several microgas turbine configurations with different tip clearances of 0.1 mm, 0.2 mm, and 0.3 mm, two different isothermal wall conditions, and two laminar-turbulent transition models were investigated to understand the particular influences of low Reynolds numbers. These influences on the overall performance of the microgas turbine were analyzed in detail. The results indicate that these configurations should be included and emphasized during the design process of the millimeter-scale microradial turbines.