Meridian Velocity Research Articles

Effect of double bypass conditions on the thermodynamic characteristics and internal flow mechanisms in a variable core cycle compression system

Effect of double bypass conditions on the thermodynamic characteristics and internal flow mechanisms in a variable core cycle compression system

Investigation of Internal Flow in Centrifugal Pump Diffuser using Laser Doppler Velocimetry (LDV) and Computational Fluid Dynamics

An unshrouded impeller is being developed for high head pumps to reduce costs and disk friction losses. On the other hand, research of internal flow in a diffuser did not clearly reveal flow structure. In this experiment, we measured the velocity distribution at the diffuser inlet and outlet plane using laser doppler velocimetry (LDV) to capture the flow from the unshrouded impeller. The relation between the total pressure and velocity distribution was evaluated. The circumferential velocity and meridian velocity were measured by short-focus LDV (Diode Laser, 74mW) about the circumferential and the height direction of the vane direction. Operating conditions in this steady measurement are at the design point flow rate. The result was compared with computational fluid dynamics (CFD) simulations carried out in steady conditions at the previously defined operation points. In this experiment, a phenomenon that the streamline moved toward the shroud side was confirmed. There was also a region where the static pressure increased on the shroud side at the diffuser inlet. This phenomenon was caused by the influence of the tip leakage flow of the unshrouded impeller downstream and the gap of the impeller’s main plate. Furthermore, two high velocity regions on the hub and shroud side at the diffuser outlet were observed because of the secondary flow in the diffuser. From the above studies, it was clarified that the ununiform flow in the diffuser was caused by the influence of the secondary flow in the unshrouded impeller.

The numerical study of the rake angle of impeller blade in centrifugal compressor

Investigated impellers have blade surfaces formed by straight generatrix. Blade profiles on shroud and disc surfaces are optimized by velocity diagram control (inviscid, quasi-three dimensional calculations). The blade profiles at hub and shroud blade-to-blade surfaces must be coordinated. A designer can choose the generatrix position at a trailing edge for it. The position is defined by the rake angle that is the angle between a trailing edge generatrix and a meridional plane. Two stages with 3D impellers, vaneless diffusers and return channels were investigated. Seven candidates of impellers of these stages with rake angles in range plus-minus 30 degrees were designed and investigated by quasi-three-dimensional inviscid calculation. CFD-calculations were made for the stages with these impellers. The optimal rake angle is minus 20 degrees for the high flow rate impeller due to lesser blade surface area and favorable meridian velocity field. Zero rake angle is optimal for the medium flow rate impeller where blade surface area is not so important. The combination of inviscid and viscid calculations is the informative instrument for further studies.

Internal Flow in a Centrifugal Pump of a Low Specific Speed with Semi-Open Impeller.

The internal flow in a centrifugal pump with semi-open impeller is visualized and measured by PTV method. In this pump, the design type number is 0.244 of low specific speed. The experimental results of two impellers whose outlet angles are 30 and 90 degree are compared. At the outlet of impeller, most of the quantity of fluid flows out along the pressure side of the vane, but some climbs over the top of the vane and flows into the suction side through the tip clearance. When the total quantity is changed, the meridian velocity distribution changes only near the tongue area, and in other area the meridian velocity is almost same. When the quantity becomes small, large vortices are produced between vanes, and this vortex reduces the tangential velocity at the outlet of impeller. This causes the reduce of theoretical head and instability in the performance curve.

Influence of the helical Impeller and the Silencer within the Scroll on Performance and Noise for Multiblade Blower.

In this paper, the velocity distributions around the impeller of a multiblade blower and noise reduction by the silencer within the scroll are investigated. It is shown that the region of small meridian velocity Cm2 at the outlet of the impeller is about 40% of the blade width b2 due to the inclination of the main flow to thce hub. It is also shown that the velocity fluctuations at the trailing edge of a blade are about 30% of the maximum velocity and that a silencer composed of sound-absorbing fiber and an air chamber within the scroll can reduce the specific sound level SLs by 2.5dB.

Velocity Distribution and Velocity Fluctuation in the Laminar-Turbulent Transition of Spherical Couette Flow.

The velocity distributions and fluctuating velocities in the laminar-turbulent transition of spherical Couette flow with only the inner sphere rotating, have been experimentally studied at two meridian angles, θ=60°and 90°, for the case of clearance ratio 0.14. The distributions of azimuthal and meridian velocity components have been considered over a wide range of Reynolds number. Logarithmic laws were obtained on the azimuthal velocity profiles in the turbulent boundary layer near the outer sphere wall for θ=60°and 90°. The phases of fluctuating velocity advance radially from the outer sphere to the inner sphere at θ=90°, but they depend on the type of disturbances at θ=60°. The phase-averaged fluctuating velocity profile in the presence of spiral TG (Taylor-Gortler) vortices differs from that in the presence of traveling azimuthal waves. Amplitude of fluctuation becomes large in the gap a little toward the outer sphere wall in the presence of spiral TG vortices at θ=60°, but a little toward the inner sphere wall in the presence of traveling azimuthal wave at θ=90°.

Velocity distributions in the turbulent boundary layers on rotating cones in axial uniform flow.

An experimental study is made for the turbulent boundary layer on the rotating cone in the axial uniform stream. Measurements of the mean velocity distributions were made at various values of the surface-to-free stream velocity ratio λb for two different cone vertex angles, 0=15°and 30°. In the polar diagram of the mean velocity distributions, the profiles are not only dependent on the local velocity ratio λ but also on θ and Rw, where Rw is the Reynolds number based on the wall velocity. The distributions of the swirl flow Richardson number reveal that the destabilizing effect of the centrifugal force is considerably stronger at θ=15°than at θ=30°. Discussions of the logarithmic velocity distributions are made for the azimuthal and the meridian velocity components as well as for the resultant velocity.

An experimental study on the aerodynamic performance of multi-blade blowers. (1st report Measurement of flow patterns within the blowers)

In this paper the velocity and the pressure distributions within the scroll of multi-blade blowers are studied. The blockage factor used for performance calculation is obtained experimentaly. It is shown that the meridian velocity cm2 at the outlet of the impeller is nonuniform in the axial direction and peripheral direction. The blockage factor is defined by taking the non-uniformity of cm2 into account, and has a minimum value of 0.38 at the width-diameter ratio b2/D2 of 0.4, and has a tendency to increase with decreasing b2/D2. The influence of the inlet diameter to the outlet diameter ratio D1/D2 and the capacity coefficient ψ on the blockage factor is small.

Velocity Profiles in the Skewed Boundary Layers on Some Rotating Bodies in Axial Flow

Velocity distributions in incompressible boundary layers on the various rotating bodies in axial flow were investigated experimentally. The rotating bodies consisted of a cylinder with nose section of three forms. Tests were run with two Reynolds numbers and the ratio of peripheral velocity of the body to main-stream velocity was in the range 0–4. The centrifugal force of the rotation considerably affected the meridian velocity profiles. Momentum thicknesses calculated from a theory with assumption of the quasi-two-dimensional velocity profile agreed well with the experiments except in the case of high rotating speed. The local shearing stress in the rotating direction is discussed.