Performance and flow condition of small-sized axial fan and adoption of contra-rotating rotors

Small-sized axial fans are used as air coolers for electric equipments. But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although it causes the deterioration of the efficiency and the increase of noise. Then the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of the performance. In the present paper, the performance and the internal flow condition of the small-sized axial fan are shown as a first step of the research for the contra-rotating small-sized axial fan and the important points to apply contra-rotating rotors to the small-sized axial fan are discussed. Furthermore, the numerical flow analysis is conducted to investigate the performance of the contra-rotating small-sized axial fan and internal flow conditions and pressure distributions are clarified and the effect of contra-rotating rotors is considered.     

Performance test and flow measurement of contra-rotating axial flow pump

An application of contra-rotating rotors has been proposed against a demand for developing higher specificspeed axial flow pump.In the present paper,the advantage and disadvantage of using contra-rotating rotorsare described in comparison with conventional type of rotor-stator,based on theoretical and experimentalinvestigations.The advantages are as follows:(1)The pump is inherently designed as smaller sized and atlower rotational speed.(2)A stable head-characteristic curve for flow rate with negative slope appears.(3)As the rear rotor rotational speed is varied as independent control of front rotor,the wider range of highperformance operation is obtained by rear rotor speed control in addition to front rotor speed control.Thedisadvantages are as follows:(1)The structure of double shaft system becomes complex.(2)The pumpperformance is inferior at over flow rate as the rear rotor loading is weakened.(3)The blade rows interac-tion from rear rotor to front rotor more strongly appears.Then the rear rotor design is a key to achievehigher pump performance.Some methods to overcome these disadvantages will be discussed in more detailstoward wider usage of contra-rotating axial flow pump in various industrial fields.     

The Self-induced unsteadiness of tip leakage flow in an axial low-speed compressor with single circumferential casing groove

Numerical investigation on the self-induced unsteadiness of tip leakage flow （TLF） for an axial low-speed com- pressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used to solve the unsteady Reynolds averaged Navier-Stokes （URANS） equations. It is found that the single grooves at various axial locations could have a large impact on the self-induced unsteadiness and the stall margin improve- ment （SMI） of compressor. The trend of SMI with groove center location demonstrates that the groove located near the mid of blade tip chord generates the best SMI. The worst groove is located about 20% Cax after the blade leading edge. The root-mean-squre of static pressure （RMSP） contours at 99.5% span and fast Fourier transform for the static pressure traces recorded in the tip clearance region for each casing are analyzed. The results demon- strate that the single groove location not only affects the oscillating strength but also the frequency of the un- steady tip leakage flow. At the near-stall point of smooth casing, the self-induced unsteadiness of TLF is enhanced most by the best grooved casing for SMI. While, the self-induced unsteadiness disappears when the worst groove for SMI is added. The characteristic frequency of TLF is about 0.55 blade passing frequency （BPF） with smooth casing. The frequency components become complicated as the single groove moves from the leading edge to the trailing edge of the blade.     

Modeling of the double leakage and leakage spillage flows in axial flow compressors

A model to predict the double leakage and tip leakage leading edge spillage flows was developed.This model was combined by a TLV trajectory model and a TLV diameter model and formed as a function of compressor one-dimensional design parameters,i.e.the compressor massflow coefficient,Ф and compressor loading coefficient,ψ,and some critical blade geometrical parameters,i.e.blade solidity,σ,stagger angle,βS,blade chord length,C,and blade pitch length,S.By using this model,the double leakage and tip leakage leading edge spillage flow could be predicted even at the compressor preliminary design process.Considering the leading edge spillage flow usually indicates the inception of spike-type stall,i.e.the compressor is a tip critical design,this model could also be used as a tool to choose the critical design parameters for designers.At last,some experimental data from literature was used to validate the model and the results proved that the model was reliable.     

Experimental and numerical investigation of the unsteady tip leakage flow in axial compressor cascade

For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.     

Numerical analysis of the tip leakage flow field in a transonic axial compressor with circumferential casing treatment

This paper reports on numerical investigations aimed at understanding the influence of
circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results
and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial
compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing
treatment configuration reveal an important modification of the vortex topology at the rotor tip
clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction
perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the
interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is
proposed.     

Experimental Investigations of the Three—Dimensional Flow in a Large Deflection Turbine Cascade with Tip Clearance

INTRoDUCTI0NThetipleakaeflowisnowrecognizedasanimpor-tantsourceoflossesinbothcompressorsandturbines,asasourceofcoolingprobleminturbinesandasourceofinstabilityincomPressorsandfans.Manyturbo-maChinimPellersarenotshroudedandtheleakaeflowthroughthetipgaPofthebladeisanunavoidablefaCtorwhichdeterioratestheperformance.Den-tonandCumpsty[1]melltionedabouttwodistinctandequallyimportantaspects.tothetipclearanceflows.First,thereisareducti0ninthebladeforce,there-fore,theworkdone.Thisoccursbecausethe…     

Investigations of Interaction of the Main Flow with Root and Tip Leakage Flows in an Axial Turbine Stage by Means of a Source／Sink Approach for a 3D Navier—Stokes Solver

IntroductionFundamental stUdies of losses in tUrbomachinery in-dicate that, besides giving rise to losses of work, leakageflows contribute to the overall creation of entropy andkinetic encrgy losses. Some entropy is created in thelabyrinth seals and in passages between the fixed androtating pats of turbomachinery. CFD computations inlabyrinth seal geometries enable the evaluation of theentropy ereation PrOCesses there. CFD-based analysis canm1nindze the mass fiow rates of the tip leakage a…     

Analysis on flow structure and improvement of heat transfer in 3D circular tube with varying axial groove turbulator configurations

Using passive devices are an efficient method to enhance streamline behavior when liquid flows through the circular pipe. The interrupted structure groove is usually used to change the flow patterns. In this analysis, a heat performance numerical technique is applied to study the characteristics of fluid flow and heat transfer of the circular pipe using different axial groove geometrical configurations with different axial groove numbers, including 2, 3, and 4, under different conditions. The number of annular grooves and circumferential positions are the important parameters to analyse with varying operating conditions, with the Reynolds number (Re) range from 1500 to 23,000. A three-dimensional coordinate pipe system is applied using tetrahedron grids. The discretization equations are obtained by deriving algebraic approximations to integral conservation equations. Results observed that using this type of passive method has a low effect on pressure dope compared to the normal one (smooth pipe). The flow change occurs near and closed to the axial groove parameters. Moreover, the Nusselt number (Nu) value for the groove turbulators was higher than the normal one, about 14.5%–21%. The friction factor (f) value for the groove turbulators was higher than the normal one, were about 7.5%–24%. Most friction losses are caused by dynamical pressure dissipation owing to more viscous losses closed to the wall surfaces. The improvement of heat performance using this type of passing method was more than 1.2%.     

Comparative analysis of two-phase flow in sinusoidal channel of different geometric configurations with application to PEMFC

The droplet dynamics inside a sinusoidal channel for PEMFC (polymer electrolyte membrane fuel cell) are investigated numerically using the VOF (volume of fluid) method. This study is done for three geometrically different channels corresponding to various non-dimensional sinusoidal distances (50, 25, 12.5, 16.7 and 8.3). The effects of key parameters like sinusoidal distance (pitch-amplitude ratio), radius of curvature and wall contact angle on the droplet removal in the flow channel are investigated. The performance of the sinusoidal as compared to the conventional channel is studied based on droplet removal rate and GDL (gas diffusion layer) surface water coverage. It is found that the droplet removal rate increases with increasing sinusoidal distance and wall contact angle. In addition, decrease in the sinusoidal distance results in a significant reduction in the average droplet speed and gas diffusion layer surface water coverage. It was also observed that broken bits of the droplet stuck on the wall corners accrued with a reduction in the wall contact angle. The curvy nature of the side walls generally induces a secondary flow effect which would be most beneficial in enhanced reactant diffusion and cell performance. It is suggested that the sinusoidal distance and wall contact angle effect on two-phase flow in a channel is highly significant. As such, needs to be considered for water management in sinusoidal channels.