Turbulent boundary layers and hydrodynamic flow analysis of nanofluids over a plate

A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simulations using CFD code are employed to investigate the boundary layer and the hydrodynamic flow.To validate the current numerical model,measurement points from published works were used,and the compared results were in good compliance.Simulations were carried out for the velocity series of 0.04,0.4 and 4 m/s and nanoparticle concentrations0.1% and 5%.The influence of nanoparticles’ concentration on velocity,temperature profiles,wall shear stress,and turbulent intensity was investigated.The obtained results showed that the viscous sub-layer,the buffer layer,and the loglaw layer along the potential-flow layer could be analyzed based on their curving quality in the regions which have just a single wall distance.It was seen that the viscous sub-layer is the biggest area in comparison with other areas.Alternatively,the section where the temperature changes considerably correspond to the thermal boundary layer’s thickness goes a downward trend when the velocity decreases.The thermal boundary layer gets deep away from the leading edge.However,a rise in the volume fraction of nanoparticles indicated a minor impact on the shear stress developed in the wall.In all cases,the thickness of the boundary layer undergoes a downward trend as the velocity increases,whereas increasing the nanoparticle concentrations would enhance the thickness.More precisely,the log layer is closed with log law,and it is minimal between Y^(+)=50 and Y^(+)=95.The temperature for nanoparticle concentration φ=5%is higher than that for φ=0.1%,in boundary layers,for all studied nanofluids.However,it is established that the behavior is inverted from the value of Y^(+)=1 and the temperature for φ =0.1% is more important than the case of φ =5%.For turbulence intensity peak,this peak exists at Y^(+)=100 for v=4 m/s,Y^(+)=10 for v=0.4 m/s and Y^(+)=8 for v=0.04 m/s.

Passive Control of Turbulent Jet Flow with Wedged Nozzle

Turbulent flow field of the free jet with circular nozzle and wedged nozzles is measured using hot wire anemometry with resolution higher than the smallest turbulence time scale. Wavelet analysis is employed to perform multi-scale decomposition of instantaneous turbulence fluctuating velocity signals, and the energy distribution of the turbulent multi-scale eddy structures over scales is studied using wavelet coefficients. Investigation of the multi-scale eddy structures of circular jet and various wedged jets reveals the transport of the energy of these wedged jets in the space from the axis to the side of the jet, as compared with the circular jet. Furthermore, not only the eddy structures at the wedge tines in the near field are crashed, but also the interactions such as eddy structure union and entrainment take place at different longitudinal and normal locations along with the development of the jets because of the existence of wedges.

Turbulence Model Investigations on the Boundary Layer Flow with Adverse Pressure Gradients

In this paper, a numerical study of flow in the turbulence boundary layer with adverse and pressure gradients （APGs） is conducted by using Reynolds-averaged Navier-Stokes （RANS） equations. This research chooses six typical turbulence models, which are critical to the computing precision, and to evaluating the issue of APGs. Local frictional resistance coefficient is compared between numerical and experimental results. The same comparisons of dimensionless averaged velocity profiles are also performed. It is found that results generated by Wilcox （2006） k-co are most close to the experimental data. Meanwhile, turbulent quantities such as turbulent kinetic energy and Reynolds-stress are also studied.

CFD Simulation of Orifice Flow in Orifice-type Liquid Distributor

In this study,a suitable CFD(computational fluid dynamics)model has been developed to investigate the influence of liquid height on the discharge coefficient of the orifice-type liquid distributors.The orifice flow in different diameters and liquid heights has been realized using the shear stress transport(SST)turbulence model and the Gamma Theta transition(GTT)model.In the ANSYS CFX software,two models are used in conjunction with an automatic wall treatment which allows for a smooth shift from a wall function(WF)to a low turbulent-Re near wall formulation(LTRW).The results of the models coupled with LTRW are closer to the experimental results compared with the models with WF,indicating that LTRW is more appropriate for the prediction of boundary layer characteristics of orifice flow.Simulation results show that the flow conditions of orifices change with the variation of liquid height.With respect to the turbulence in orifice,the SST model coupled with LTRW is recommended.However,with respect to the transition to turbulence in orifice with an increase in liquid height,the predictions of GTT model coupled with LTRW are superior to those obtained using other models.

Effect of wind-current interaction on ocean response during Typhoon KAEMI(2006)

The Weather Research and Forecasting （WRF） model, the Princeton Ocean Model （POM）, and the wave model （WAVEWATCH III） are used to develop a coupled atmosphere-wave-ocean model, which involves different physical pro- cesses including air-forcing, ocean feedback, wave-induced mixing and wave-current interaction. In this paper, typhoon KAEMI （2006） has been examined to investigate the effect of wind-current interaction on ocean response based on the coupled atmosphere-ocean-wave model, i.e., considering the sea surface currents in the calculation of wind stress. The results show that the wind-current interaction has a noticeable impact on the simulation of 10 m-winds. The model involving the effect of the wind-current interaction can dramatically improve the typhoon prediction. The wind-current interaction prevents excessive momentum fluxes from being transferred into the upper ocean, which contributes to a much smaller turbulence kinetic energy （TKE）, vertical diffusivity, and horizontal advection and diffusion. The Sea Surface Temperature （SST） cooling induced by the wind-current interaction during the initial stage of typhoon development is so minor that the typhoon intensity is not very sen- sitive to it. When the typhoon reaches its peak, its winds can disturb thermocline, and the cold water under the thermocline is pumped up. However, this cooling process is weakened by the wind-current interaction, as ocean feedback delays the decay of the typhoon. Meanwhile, the temperature below the depth of 30 m shows an inertial oscillation with a period about 40 hours （-17°N） when sudden strong winds beat on the ocean. Due to faster currents, the significant wave height decreases as ignoring the wind-current interaction, while this process has a very small effect on the dominant wave length.

Numerical analysis of periodic flow unsteadiness in a single-blade centrifugal pump

In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in detail by defining unsteady intensity and turbulence intensity in both rotor and volute domains under design condition Q=33 L s 1.The results show that the distributions of flow unsteadiness are the functions of impeller rotating angle and have complex unsteady characteristics.The obvious T u fluctuations can be also observed for different impeller positions.In addition,time-averaged unsteady intensity and time-averaged turbulence intensity were calculated by averaging the results of each mesh node for entire impeller revolution period to evaluate the strength distributions of flow unsteadiness directly and comprehensively.The accumulative results of an impeller revolution can directly show the positions and strength of the flow unsteadiness and turbulence intensity in both rotor and stator domains which can be an important aspect to be considered in the single-blade pump optimum design procedure for obtaining more stable inner flow of the pump and decreasing flow-induced vibration and noise.The flow unsteadiness in the side chamber cannot be neglected for an accurate prediction of the inner flow of the pump,and the optimizing design procedure for a single-blade pump impeller will not be accurate using CFD tool if the unsteady flow phenomenon in the side chamber is not considered.