轴流风速下旋流喷嘴的外流场实验研究

为解决烯烃厂急冷器结焦问题,建立旋流喷嘴实验模型,采用高速摄像系统跟踪记录喷雾场的形成过程以及测量雾滴的大小,并利用激光多普勒测试系统对喷嘴的外流场速度分布进行测量.实验结果表明:当喷嘴出口压力大于0.7MPa时,雾滴粒径变小的趋势加快,雾化效果发生明显转变,油浆经汽化产生的裂解气越多,从而提高裂解气的产量;当轴向风速大于10m/s时,喷雾场轴向速度增加显著并且趋于均匀化,油浆经过喷嘴后形成的雾滴在急冷器内停留的时间相对降低,减少了结焦发生的可能性.

CHARACTERISTICS OF FAN STALLING BASED ON CORRELATED DIMENSIONS

Different from the previous qualitative analysis of linear systems in time and frequency domains, the method for describing nonlinear systems quantitatively is proposed based on correlated dimensions. Nonlinear dynamics theory is used to analyze the pressure data of a contrarotating axial flow fan. The delay time is 18 and the embedded dimension varies from 1 to 25 through phase-space reconstruction. In addition, the correlated dimensions are calculated before and after stalling. The results show that the correlated dimensions drop from 1. 428 before stalling to 1. 198 after stalling, so they are sensitive to the stalling signal of the fan and can be used as a characteristic quantity for the judging of the fan stalling.

MEASUREMENT AND VISUALIZATION OF FLOW FIELD IN AXIAL FLOW FAN

An experimental investigation associated with the basic fluid mechanics in an axial flow fan is described in this paper. The flow field in the tip region has been studied by laser Doppler anemometer (LDA) and flow visualization technique. Some experimental data and images are interpreted to understand the complex interactions between the annulus wall boundary layer and the leakage flow. It shows that the vortex inside the blade passage is produced by the separation of annulus wall boundary layer rather than the rolling up of leakage flow.

Numerical simulation investigation on pressure loss of diffusion tank of axial main fan

Based on the engineering application, the angle range of rectifying airflow unit attaching diffusion tank is from 2.5° to 7.5°. In the range of average inlet velocity of 25.0 m/s to 55.0 m/s of diffusion tank, numerical simulations of diffusion tank were done. The results of numerical simulations of diffusion tank are shown as follows： ③ In cases of the inlet velocity range from 25.0 m/s to 55.0 m/s, and the angle range of rectifying airflow unit from 2.5° to 7.5°, the average value of pressure losses decreases to the minimum when the angle is 4.5°.② In cases of the inlet velocity of 35.0 m/s, the pressure loss of diffusion tank decreases to the minimum when the angle of rectifying airflow unit is 5.5°. ③ As far as there are different angles of rectifying airflow unit, pressure loss increases gradually along with the addition of inlet velocity.

Effects of circumferential configuration concerning splitter blade on the aerodynamic performance in a transonic axial fan

For a certain type of transonic axial fan, the flow field of a fan rotor with splitter blade was computed by numerical simulation, and the shape of the rotor was modified. The effects of different circumferential distributions concerning the splitter cascades upon the aerodynamic performance were investigated. The studies show that the optimum splitter cascade is not very close to the suction side of main blade. The load between the main blade and the splitter blade can be soundly distributed in terms of the adjustment of circumferential position of the splitter blade. The best aerodynamic performance can be successfully obtained according to the optimum shape of the expanding fluid channel reasonably formed by the splitter blade and the main blade.

Numerical Investigation of a High-subsonic Axial-flow Compressor Rotor with Non-axisymmetric Hub Endwall

The major source of loss in modem compressors is the secondary loss. Non-axisymmetric endwall profile contouring is now a well established design methodology in axial flow turbines. However, flow development in axial compressors is differ from turbines, the effects of non-axisymmetric endwall to axial compressors requires flow analysis in detail. This paper presents both experimental and numerical data to deal with the application of a non-axisymmetric hub endwall in a high-subsonic axial-flow compressor. The aims of the experiment here were to make sure the numerically obtained flow fields is the physical mechanism responsible for the improvement in efficiency, due to the non-axisymmetric hub endwall. The computational results were first compared with avail- able measured data of axisymmetric hub endwall. The results agreed well with the experimental data for estima- tion of the global performance. The coupled flow of the compressor rotor with non-axisymmetric hub endwall was simulated by a state-of-the-art multi-block flow solver. The non-axisymmetric hub endwall was designed for a subsonic compressor rotor with the help of sine and cosine functions. This type of non-axisymmetric hub end- wall was found to have a significant improvement in efficiency of 0.45% approximately and a slightly increase for the total pressure ratio. The fundamental mechanisms of non-axisymmetric hub endwall and their effects on the subsonic axial-flow compressor endwall flow field were analyzed in detail. It is concluded that the non-axisymmetric endwall profiling, though not optimum, can mitigate the secondary flow in the vicinity of the hub endwall, resulting in the improvement of aerodynamic performance of the compressor rotor.

Analysis of Tonal Noise Generating Mechanisms in Low-Speed Axial-Flow Fans

The present paper reports a comparison of experimental SPL spectral data related to the tonal noise generated by axial-flow fans.A nine blade rotor has been operated at free discharge conditions and in four geometrical configurations in which different kinds of tonal noise generating mechanisms are present:large-scale inlet turbulent structures,tip-gap flow,turbulent wakes,and rotor-stator interaction.The measurements have been taken in a hemi-anechoic chamber at constant rotational speed and,in order to vary the acoustic source strength,during low angular acceleration,linear speed ramps.In order to avoid erroneous quantitative evaluations if the acoustic propagation effects are not considered,the acoustic response functions of the different test configurations have been computed by means of the spectral decomposition method.Then,the properties of the tonal noise generating mechanisms have been studied.To this aim,the constant-Strouhal number SPL,obtained by means of measurements taken during the speed ramps,have been compared with the propagation function.Finally,the analysis of the phase of the acoustic pressure has allowed to distinguish between random and deterministic tonal noise generating mechanisms and to collect information about the presence of important propagation effects.

Contributions of the Secondary Jet to the Tangential Velocity Distribution and to the Collection Efficiency of the Fixed Guide Vane Type Axial Flow Cyclone Dust Collector

In order to control the maximum tangential velocity V?m(m/s)of the turbulent rotational air flow and the collection efficiencyηc(%)using the fly ash of the mean diameter X R50=5.57?m,two secondary jet nozzles were installed to the body of the axial flow cyclone dust collector with the body diameter D1=99mm.Then in order to estimate V?m(m/s),the conservation theory of the angular momentum flux with Ogawa combined vortex model was applied.The comparisons of the estimated results of V?m(m/s)with the measured results by the cylindrical Pitot-tube were shown in good agreement.And also the estimated collection efficienciesηcth(%)basing upon the cut-size Xc(?m)which was calculated by using the estimated V?m(m/s)and also the particle size distribution R(Xp)were shown a little higher values than the experimental results due to the re-entrainment of the collected dust.The best method for adjustment ofηc(%)related to the contribution of the secondary jet flow is principally to apply the centrifugal effect?c(1).Above stated results are described in detail.