Kraeva E.M.

Siberian State Aerospace University, Russia

А vortex zone in the channels of high-speed

centrifugal pumps

High-speed low-rate centrifugal pumps with rotor angular speed up to 10000 rad/s are wide used in structures of turbo-pump units of liquid-propellant engine of low traction and energy installation of aircrafts. That is because they have wide range of operating conditions. E.g., if the rotor angular speed rad/s, the value amounts to under Reynolds number . The feed decreases in such pumps simultaneously with rotor angular speed increase leads to decrease below value . It is rating value for closed-type impeller rotary pumps [1]. Therefore high-speed rotary pumps with semiopen-type impeller are used wide.

In centrifugal impellers of semi-open and open types there is unevenness of flow and vortex interaction along the radius of main fluid flow and in the lateral axil of the pump. The vanes convey energy to the fluid flow, a portion of which is moving with a lag from the main one in the lateral axil. In the result a flow is formed as in the channel behind the bluff body. This flow is characterized by the appearance of return currents and vortices. [2] This process is determined by the ratio of width to length of the channel, the thickness of the boundary layer on the walls and the relative height of the vane. The interaction of flows in channels and axil leads to the appearance of circulating currents in the area behind the vane.

Picture of the flow between the rotating impeller with the end vanes and sleek hull is quite complex. The liquid contained in the field of grooves is exposed to direct power impact of the vanes. The fluid in the axial gap is twisted by the forces of friction and slip relative to vanes of the impeller. Thus at the same radius the particles of the fluid are moved with different speed in the channels and the axial gap that causes a relative movement in the radial and axial directions. In the area of vanes there is a radial expendable flow towards the periphery.

Since the coefficient of flow swirling φ <1, we always have a relative motion of the fluid and the vanes of the impeller, that certainly leads to the formation of circulation zone in the channels of the impeller as a result the flow wraps around cavity.

One of the characteristics of the vortex zone is the ratio of the circumferential speed to the incoming flow speed at the outer border of the vortex zone

(1)

The analytical calculation of the variable on the data of the work [2] for the channel of an impeller gives the value . However, the experimental data presented in the same paper indicate a significant difference between the calculated value from the experienced one, in the direction of increasing the experienced value. That difference the author of [2] explains by the influence of boundary layers.

When testing a cylindrical fluid coupling on the water, in [3] there is a marked clearly expressed vortex structures in cavities of the rotating cylinder.

The analysis of experiments on determining the estimated value , as described in this paper, gives us a basis to take it to our research by 0.3.

A typical picture of variation in flow speed through the gap and the inter-vane channel (at a ratio of width to depth of the channel ) (Figure 1) taking into account on visualization tests confirmed the presence the three zones of flow: zone of the flow 1 flowing over the channel; the mixing zone 2 and zone 3 of the circular vortex flow in the channel region, where the speed .

Figure 1 – Experimental and theoretical profiles of the circumferential speed in the channel region along the radius of the vortex zone: 1 – the zone of the flow in the axial gap; 2 – the mixing zone; 3 – the zone of the vortex flow;

- experimental points [3]

In order to clarify the main features of the hydrodynamics in semi-open channels of an impeller, we conducted the series of experiments, including those on the visualization of the flow in these impellers.

This work was supported by the grant of the President of the Russian Federation МК – 1371.2013.8.

References

1. Kraev M.V., Lukin V.A., Ovsyannikov B.V. Low-rate pumps of air and space system [in Russian], Mashinostroenie, Moscow, 1985.

2. Abramovich G.N. The theory of turbulent jets. – М. : Phismathgiz, 1960. – 716 p.

3. Levin А.А., Perelman R.G. Investigation of a cylindrical fluid coupling / Investigation of aggregates operating on alkaline metals: MAI. – 1969. – V. 193. – P. 57–102.