Study on the effect of separation and reattachment flow between blades on fan noise

With the growth of the EV/HV market, the main cause of cabin noise has changed from engine driving sound to air conditioner noise. The blower noise is the largest in the air conditioner noise, and the noise reduction is urgent. Separated and reattached flows between fan blades are considered to be the main sources of blower noise. In the past, we tried to reduce the noise by reducing the separation. This time, the blade shape to further reduce the separation was produced and evaluated. As a result, the noise was greatly reduced, but a new problem was found that there was a flow velocity condition in which the noise increased despite the small separation. Therefore, we visualized the flow between blades by PIV, investigated the state of separated and reattached flow in detail, and investigated the factors related to noise increase and decrease by measuring noise and pressure fluctuation of blade surface simultaneously. As a result, it was found that the noise generation condition in the separation reattachment flow between blades is not only the size of separation but also the distance of separation shear layer from blade surface and the strength of vortex generated in shear layer.

Influence of Non-Newtonian Rheology on Mass Transfer From a Biofluid in Separated and Reattached Flows

Influence of the rheological model selection on the flow and mass transfer behavior of human blood in a separated and reattached flow region is investigated. Newtonian and non-Newtonian hemorheological models that account for the yield stress and shear-thinning characteristics of blood are used. The conservation of mass, momentum, and species equations as well as the Herschel-Bulkley constitutive equation are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the impact of flow restriction and rheological modelling on blood-borne oxygen exchange with the confining walls. The wall mass transfer rates within the separated and reattached regions display a strong dependency on the used hemorheological model. Newtonian and non-Newtonian models result in a peak wall mass transfer rate within the recirculation region. However, non-Newtonian models that account for the yield stress and shear-thinning effects predict a substantial, highly localized, drop in the wall mass transfer rates of oxygen, at the reattachment point.

Effect of Prandtl Number on Convective Heat Transfer in the Separated and Reattached Flow Region on a Blunt Flat Plate

The understanding of the heat transfer in separated and reattached flows is essential for a wide range of engineering applications. The majority of the literature uses air as a working fluid for experimental and numerical investigations. The blunt flat plate configuration offers a generic starting point for flow and heat transfer investigations in separated and reattached flow regions. The present contribution is dealing with experimental measurements of the flow and convective heat transfer within the separated and reattached flow on a blunt flat plate. The blunt plate was placed inside a closed circuit water tunnel. By this approach, in comparison with reliable literature data for air, it was possible to investigate the effect of the Prandtl number on the convective heat transfer of blunt flat plate.

Lattice Boltzmann method for axisymmetric turbulent flows

A lattice Boltzmann model for axisymmetric turbulent flows is developed. It is a further development of the enhanced axisymmetric lattice Boltzmann method (AxLAB®). The turbulent flow is efficiently and naturally simulated through incorporation of the standard subgrid-scale (SGS) stress model into the axisymmetric lattice Boltzmann equation in a consistent manner with the lattice gas dynamics. The model is verified by applying it to three typical cases in engineering: (i) pipe flow through an abrupt axisymmetric constriction, (ii) axisymmetric separated and reattached flow and (iii) pulsatile flows in a stenotic vessel. The numerical results obtained using the present method are compared with experimental data and other available numerical solutions, indicating good agreements. The model is simple and is able to predict axisymmetric turbulent flows at good accuracy.

The Flow Behavior of a Biofluid in a Separated and Reattached Flow Region

The flow behavior of human blood in a separated and reattached flow region is investigated. Hemorheological data that account for the yield stress and shear-thinning non-Newtonian characteristics of blood are used. The governing mass and momentum conservation equations along with the Herschel–Bulkley constitutive equation are solved numerically using a finite-difference scheme. Two inflow velocity profiles are considered, uniform and fully developed (fd) ones. A parametric study is performed to reveal the impact of inflow velocity profile, upstream flow restriction, and rheology on the recirculation strength and reattachment characteristics of the flow field. Uniform inflow conditions result in larger relative recirculation intensity, in comparison with the fd ones, only for a moderate upstream flow restriction. The separated flow region size in the case of a fd inflow is always larger than the one observed for uniform inflow. Larger separated flow regions with stronger flow recirculation, are predicted by the Newtonian (N) model in comparison with the yield shear-thinning (HB) model for all studied inflow and upstream restriction conditions. The separated flow region size displays a stronger dependency on the inflow velocity profile and upstream flow restriction, in comparison with the observed dependency on the used hemorheological model.

Inflow Conditions and the Wall Shear Stress Characteristics of a Biofluid in Separated and Reattached Flow Regions

The influence of inflow conditions and human blood rheology on the wall shear stress distribution in a confined separated and reattached flow region is investigated. The governing mass and momentum conservation equations along with the Herschel-Bulkley rheological model are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the influence of uniform and fully-developed inflow velocity profiles on the wall shear stress (WSS) characteristics using hemorheological models that account for the yield stress and shear-thinning non-Newtonian characteristics of human blood. The highest WSS or WSSmax, is always observed inside the flow separation region at a location corresponding to that of the corner vortex center. Uniform inflow results in higher WSSmax values in comparison with fully-developed inflow for moderate upstream flow restrictions. The opposite trend is observed for severe flow restrictions. Uniform inflow always results in smaller flow separation regions and WSSmax values at locations closer to the flow restriction plane. The yield shear-thinning hemorheological model always results in the highest observed peak WSS. The yield stress impact on WSS distribution is most pronounced in the case of severe restrictions to the flow.

The Impact of Hemorheology on Wall Shear Stress in a Separated and Reattached Flow Region

Wall-bounded separating and reattaching flows are encountered in biological applications dealing with blood flows through arteries and prosthetic devices. Separated and reattached flow regions have been associated in the past with the most common arterial disease, atherosclerosis. Previous studies suggest that local wall shear stress (WSS) patterns affect the location and progression rate of atherosclerotic lesions. A parametric study is performed to investigate the influence of hemorheology on the wall shear stress distribution in a separated and reattached flow region. Recent hemorheological studies quantified and emphasized the yield stress and shear-thinning non-Newtonian characteristics of unadulterated human blood. Numerical solutions to the governing equations that account for yield stress and shear-thinning rheological effects are obtained. A low WSS region is observed around the flow reattachment point while a peak WSS always exists close to the vortex center. The yield shear-thinning hemorheological model always results in the highest observed peak WSS. The yield stress impact on WSS distribution is most pronounced in the case of severe restrictions to the flow.