Guojun Li

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.

Multiobjective Optimization Approach to Turbomachinery Blades Design

This paper presents an automated optimization design methodology for turbomachinery blades using multiobjective evolutionary algorithms (MOEAs) and Navier-Stokes solver. 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. Two design cases of the 2D and 3D compressor blade are used to demonstrate the presented methodology performance. A 2D axial compressor blade is optimized for maximization of the static pressure rise and minimization of the total pressure loss at the fixed flow condition. The Pareto solutions are obtained using the presented optimization algorithm. The detailed analysis between the certain Pareto solutions with the higher static pressure rise and the lower total pressure loss and the initial design are illustrated. A 3D centrifugal compressor impeller blade is optimized as the second case. The maximization of the pressure rise and blade load and minimization of the rotational total pressure loss at the given flow conditions are worked as the design targets. The present method obtains many reasonable Pareto optimal designs that outperform the original centrifugal impeller at the designed condition.Copyright

On the Key Parameters of an Interior Sloshing Absorber for Vibration Suppression

The vibration reduction for a cantilever beam with an interior sloshing absorber is numerically simulated using an implicit coupling approach of segregated solvers. The sloshing liquid damps the vibration by allowing the sloshing force to lag behind the displacement phase of the beam. The sloshing in the absorber is analyzed both theoretically and numerically. The results show that the impact of free sloshing on the forced sloshing causes the phase to be lagged behind when the free frequency is lower than the frequency of forced vibration. A range of values are considered for the parameters of the absorber and system vibration in the simulations to investigate their effects on the suppression capability of the absorber. In order to explain the effects of the parameters, two new parameters γ and κ are defined to represent the phase lag and magnitude of the sloshing force, respectively. Their applicability is confirmed by a series of numerical simulations. The results reveal the main mechanism of vibration suppression, providing a theoretical basis for optimizing the design of the interior absorber.

Performance Analysis of 15 kW Closed Cycle Ocean Thermal Energy Conversion System With Different Working Fluids

Closed cycle ocean thermal energy conversion (CC-OTEC) is a way to generate electricity by the sea water temperature difference from the upper surface to the different depth. This paper presents the performance of a 15 kW micropower CC-OTEC system under different working fluids. The results show that both butane and isobutane are not proper working fluids for the CC-OTEC system because the inlet stable operating turbine pressure is in a very narrow range. R125, R143a, and R32, especially R125, are suggested to be the transitional working fluids for CC-OTEC system for their better comprehensive system performance. Moreover, it is recommended that propane should be a candidate for the working fluid because of its excellent comprehensive properties and environmental friendliness. However, propane has inflammable and explosive characteristics. As for the natural working fluid ammonia, almost all performance properties are not satisfactory except the higher net output per unit sea water mass flow rate. But ammonia has relative broader range of the stable operating turbine inlet pressure, which has benefits for the practical plant operation.

Numerical Simulation of Wet Steam Condensing Flow Based on a Two-fluid model

A two-fluid model of wet steam condensing flow was established, in which the effect of velocity slipping and coupling between the steam and liquid phases as well as the turbulent diffusion were taken into account. Referred to the transport equation theory of particle’s turbulent kinetic energy, the SST k-ω-k p two-phase turbulence model was derived from the SST k-ω turbulence model considering the turbulent characteristics of the internal flow in steam turbine. In this model, the quasi-fluid concepts were introduced in order to analyze the turbulent transport properties of the particle phase, such as the viscosity, the thermal conductivity and the diffusion coefficient. Numerical simulation of wet steam flow with spontaneous condensation in a two-dimensional cascade indicates that the results predicted by the present model agree well with the experimental data, and show more reasonable flow details in many local regions. A three-dimensional numerical simulation of the wet steam flow in a turbine cascade indicates that substantive nucleation emerges firstly near the end wall where the wet steam flow reverts to equilibrium state earlier than that in the middle section. The outlet Mach numbers of the two phases along the blade height are different due to the presence of vortices. The model developed in this paper includes the effects of interactions between the two phases, and improves the precision of numerical simulation of wet steam flow with condensation.

Effects of Pressure Ratio and Sealing Clearance on Leakage Flow Characteristics in the Rotating Honeycomb Labyrinth Seal

Honeycomb stepped labyrinth seals in turbomachinery enhance aerodynamic efficiency by reducing leakage flow losses through the clearance between rotating and stationary components. The influence of pressure ratio and sealing clearance on the leakage flow characteristics in the honeycomb stepped labyrinth seal is numerically determined. The geometries investigated represent designs of the honeycomb labyrinth seal typical for modern turbomachinery. The leakage flow fields in the honeycomb and smooth stepped labyrinth seals are obtained by the Reynolds-Averaged Navier-Stokes solution using the commercial software FLUENT. Numerical simulations covered a range of pressure ratio and three sizes of sealing clearance for the honeycomb and smooth stepped labyrinth seals. The numerical discharge coefficients of the non-rotating honeycomb and smooth stepped labyrinth seals are in good agreement with previous experimental data. In addition rotational effects are also taken into account in numerical computations. The numerical results show that the leakage flow rate increases with the increasing pressure ratio at the fixed sealing clearance for the rotating and non-rotating honeycomb labyrinth seal. The influence of the sealing clearance on the leakage flow pattern for the rotating and non-rotating honeycomb labyrinth seal are observed. Moreover, the similar leakage flow rates are obtained at the same flow condition between the rotating and non-rotating honeycomb labyrinth seal due to the honeycomb acts to kill swirl velocity development for the rotating honeycomb labyrinth seal.© 2007 ASME

SIMULATIONS OF DROPLET FORMATION IN A T-JUNCTION MICRO-CHANNEL USING THE PHASE FIELD METHOD

Micro-fabrication techniques are developed rapidly because they offer numerous benefits for chemical and biological industries. Numerical simulations (based on incompressible Navier–Stokes equations) are presented of the two-phase flow in a cross-flowing T-junction micro-channel using the phase field method and the results are in agreement with experimental measurements. The leakage rate in the gap between the droplet and lower wall decreases during the droplet formation, the relationship between the leakage rate and the derivative of the up-stream droplet size is obtained, which is applicable when the droplet contacts with the lower wall on the wetted conditions or expands to the up-stream in the main channel. The droplet formation is related to several factors, including the capillary number, the contact angle, the flow rate ratio, and the micro-channel shape. The critical capillary number could distinguish between the squeezing and dripping regimes for the generation of different kinds of droplets. The...

The Effect of Vortex Core Distribution on Heat Transfer in Steam Cooling of Gas Turbine Blade Internal Ribbed Channels

Steam has already been used as coolant of gas turbine blade internal cooling. A lot of investigations have been carried out to research the heat transfer performance of steam in ribbed rectangular channels. However, the micro-structure of the flow field especially the vortex distribution is not very clear. As the vortex caused by ribs is one of the main factors that enhance heat and mass transfer, it is very necessary to investigate the distribution of vortex in steam-cooled ribbed channels. The numerical simulation of steam flow field in 45° rib channels were carried out by using ANSYS CFX commercial program. The inlet Reynolds numbers are 30000 and 60000. The wall heat flux and inlet static pressure is 10kW/m2 and 0.3MPa, respectively. In order to find out the distribution and shape of all the main vortices, the technology of vortex core is applied, which is based on the critical point theory and Eigen-values of velocity gradient tensor. The distribution and shape of vortex core clearly indicates that the heat transfer strength of vortices positions is relatively higher than other places. There are four high strength vortices at the near-wall region between every two neighbored ribs. At the side wall which is located at the front side of ribs, high strength vortex exists and washes over the most part of the side wall. In the main flow region, the secondary flow caused by angled ribs can also be seen. The heat and mass transfer performance of steam in angled rib channels can be illustrated by the location and shape of vortex core.Copyright

NUMERICAL SIMULATION OF RAYLEIGH–TAYLOR INSTABILITY BASED ON AN IMPROVED PARTICLE LEVEL SET METHOD

An improved particle correction procedure for particle level set method is proposed and applied to the simulation of Rayleigh–Taylor instability (RTI) of the incompressible two-phase immiscible fluids. In the proposed method, an improved particle correction method is developed to deal with all the relative positions between escaped particles and cell corners, which can reduce the disturbance arising in the distance function correction process due to the non-normal direction movement of escaped particles. The improved method is validated through accurately capturing the moving interface of the Zalesaks disk. Furthermore, coupled with the projection method for solving the Navier–Stokes equations, the time-dependent evolution of the RTI interface over a wide range of Reynolds numbers, Atwood numbers and Weber numbers are numerically investigated. A good agreement between the present results and the existing analytical solutions is obtained and the accuracy of the proposed method is further verified. Moreover, the effects of control parameters including viscosity, density ratio, and surface tension coefficient on the evolution of RTI are analyzed in detail, and a critical Weber number for the development of RTI is found.

Effects of shape factors on flow and heat transfer in corrugated-undulated channels with sinusoidal waves

Abstract Three-dimensional numerical simulations of flow and heat transfer in crosscorrugated-undulated channels with sinusoidal waves under laminar flow conditions are reported. This simulation adopts the multi-channel computational domain. The main aim of this study is to investigate the effects of shape factors of the undulated plate and Reynolds number (Re) on flow and heat transfer. Data for Nusselt number (Nu) and friction factor (f) are presented for air flowrates in the range 100 ≤ Re ≤ 1500. Performance evaluation and analysis of entry effects are made. The results confirm that the effects of both undulation height and Re are significant but that the effect of undulation pitch is much less marked. As the height of the undulated plate increases, f decreases; the effect of the undulation pitch on f has similar characteristics. Minimum f is obtained in the largest height (CP-UH0) and the largest pitch (CP-UP0) channels, respectively. For the heat transfer, the results indicate that the average Nu with increasing height first decreases and then increases at the same Re, and the maximum average Nu is achieved on the CP-UH0 geometry; the average Nu, however, is nearly independent of the pitch. The maximum local Nu (Nu C or Nu U) is located in the upstream region of the crest of the conjugate channel and near the downstream end of the trailing edge. The minimum local Nu is situated around the four corners where the top plate touches the bottom one. Performance evaluation shows that the channels having the largest undulation height or largest pitch are optimal. The average Nu having the largest undulation height (CP-UH0) geometry is about ten times higher and the concomitant f is 18.52 times higher, when compared with a straight channel having a square cross-section. With the same reference channel, the average Nu having the largest undulation pitch (CP-UP0) geometry is 9.11 times higher at the cost of a 22.12 times higher f.