WO2010042077A1

WO2010042077A1 - Centrifugal turbo machine rotor

Info

Publication number: WO2010042077A1
Application number: PCT/SI2009/000034
Authority: WO
Inventors: Brane Sirok; Gasper Benedik; Aljosa Mocnik
Original assignee: Domel, Elektromotorji In Gospodinjski Aparati, D.D.
Priority date: 2008-10-06
Filing date: 2009-08-19
Publication date: 2010-04-15
Also published as: SI22894A

Abstract

The subject of the invention is a new design of a centrifugal turbo machine rotor, such as a blower, pump or fan, which is generating the pressure difference and volume flow of fluid. The rotor (1) of the centrifugal turbo machine of the invention has a lower wall or hub (4), which is attached to the shaft (5) of the turbo machine, characterised in that a structure of porous or cellular material fills in at least part of the rotor between the rotation axis and the circumference of the rotor, whereas the driven fluid travels in the radial direction through a porous or cellular material (2).

Description

CENTRIFUGAL TURBO MACHINE ROTOR

The subject of the invention is a new design of centrifugal turbo machine rotor, such as blower, pump, fan, which generates the pressure difference and volume flow of fluid.

Technical problem

Technical problem that the invention solves is how to design and make the centrifugal turbo machine rotor, which will provide a minimum noise without discrete frequencies at low volume fluid flow rates, high efficiency in a wider volume flow range and steady fluid flow without pressure pulsations.

State of the art

Typically, centrifugal turbo machine rotors consisting of a hub - the lower wall, which is attached to the shaft turbo machine and the upper wall and between them at the circumference periphery arranged blades, through which torque is transmitted from the rotor, of motor to the driven fluid, that is gas or liquid. In the semi-open rotors there is no upper wall, the sealing is performed with a small gap between the rotor and turbo machine cover. The common feature of working centrifugal turbo machinery is that inputted mechanical work is transferred through the rotor blades in increase of stagnation pressure and consequently increases the enthalpy of medium, i.e. fluid.

Rotor blades thus providing the basic function of the blower, this is transfer of energy to the fluid, but during this transfer there are certain phenomena that are undesirable. The pressure on one side of the blade is higher than the pressure on the other side, what is causing pulsations in the exit flow of fluid and increased noise. The occurrence of »blade passing« is obvious in the application of bladed diffuser, which is used to reduce kinetic energy of fluid and thus to increase the static pressure. The interaction between moving rotor blade and static stator blade causes pressure impulse and consequently the noise generation with distinctive discreet frequency. This effect was attempted to be reduced or at least made less obvious in a number of patents, such as described in patent documents, for example US6166462, GB656430, FR2780454, US5340275, US4174020, US4279325, US005454690A, SI21831A, SI21778A2 etc. Working of turbo machine outside of the optimal point due to an unfavourable direction of fluid flow on bladed rotor results in flow separation and recirculation, what reduces the efficiency and generates a coherent vortex structures in specific frequency ranges as well as broadband turbulent noise. In the extremely low flow range it leads to stagnation vortices and even to reverse flow and consequently to air flow pulsations and also to 10-20 dB increase of noise according to the optimal operation point of turbo machine.

Similar phenomena occur in the pumps where increased local speeds of fluid results, in addition to already mentioned phenomena, in cavitation and, consequently, in increased cracking noise, increased vibrations, pressure drop, material erosion during bubble implosion and ultimately failure of the pump.

Nikola Tesla in patent US 1061142 describes the innovative approach for transfer of energy that does not take place through the rotor blades but through the boundary layer of parallel co rotating disc. Principle is useful for blowers, turbines and pumps. The advantages of the device are the absence of discrete frequencies in the noise spectrum, robustness and simplicity of the machine, possibility of use with fluids with high viscosity, abrasive particles or for non- Newtonian fluids. The efficiency of energy transfer between the discs is relatively high, however, high losses occur on exit and entrance of rotor. The total aerodynamics section efficiency of turbo machine does not exceed 60% and drops very quickly outside of optimal working point, and consequently broader commercial application of the solution did not occur.

The task and objective of the invention is the design of such centrifugal turbo machine rotor, which will not create pressure differences on both sides of the blade, and consequently one of noise generating mechanism will not occur, when used in conjunction with the diffuser »blade passing« will not occur and the recirculation flow stagnation vortices will not be present, high efficiency will be achieved in a wider range of flow rates, exit fluid flow will be uniform, without the pressure pulsations, noise will be broadband or so-called »white noise« without the occurrence of discrete frequencies.

The task is solved with the centrifugal turbo machine rotor upon an independent patent claim. Description of invention

Invention will be described on the basis of preferred embodiment and pictures, which show: Figure 1: elevation and section of preferred embodiment of a rotor of invention, Figure 2: preferred embodiment of a rotor partially filled with porous material, Figure 3: photo of the structure of the open-cell porous material, Figures 4a to 4g: different embodiment of periodic cellular material.

Figure 1 shows preferred embodiment of such a new rotor design of centrifugal turbo machine, where is the energy from the rotor 1 to the driven fluid not transmitted through the rotor blades, but through a rotating structure of porous material 2. Porous material 2, with which is partially or completely filled rotor 1 of turbo machine, is mechanically sufficiently solid, high-porous material with open cell structure. Photo of such a material is in figure 3. Porous material 2 is preferably inserted between the lower wall or the hub 3 and the upper wall 4, so that is the fluid flow in the axial direction not possible. The rotor is attached to the shaft of the motor, preferably electro motor, and rotates around the axis 5. Fluid enters into the rotor axially in the direction 6 and exit in the radial direction 7.

Rotor in invention is thus assembled of the hub or the lower wall, which is attached to the shaft of turbo machine and the upper wall between them and the structure of porous material through which torque from the rotor of the motor to the driven fluid is transmitted. Semi-open rotors have no front wall; the sealing is done with a small gap between the rotor and blower covering. The structure of porous material fills in the radial direction from rotation centre axis towards the periphery of the rotor at least a part of the rotor, and this to the perimeter of rotor.

According to invention a porous structure can be constructed in one piece or as an assembly of several components of any shape. Also, the structure of porous material can be made of any shape, for example as an inlet in the form of blades, contour of upper or lower wall can be parabolic or other section.

Porous material is composed of solid material, preferably of metal, polymer or ceramic, and of fluid, preferably gas or liquid. The density of porous material is preferably between 5% and 30% density of solid material. Porous materials with higher density have generally a higher -A- mechanical strength, but also the pressure losses occurred during the fluid flow are accordingly higher. For choice of material it is necessary to find a compromise between mechanical strength and fluid flow losses. Porous material shown in figure 3 has an open cell structure, which means that the pores in the material are interconnected; consequently it is permeable to fluid flow. Porous material has an average diameter of the cells between 0.1 and 20 mm, preferably between 1 and 4 mm. Mentioned material is due to the development of appropriate production technologies becoming increasingly market attractive.

As a porous material is also possible to use periodic or non-periodic cellular material, which is an assembly of various components, preferably defined geometric shapes. The term cellular material relates to the material of the cell structure. The basic elements of assembly parts are for example square, block, hexagon, triangle, pyramid or other periodical or periodical-like shapes. Some of preferred embodiments of the periodic cellular material for the manufacture of rotor after the invention are shown in figures from 4a to 4j. These materials can also be anisotropic. Permeability for fluid flow can be dependent from fluid flow direction. At the appropriate design it is in this way possible to achieve a maximum permeability of material in the direction of fluid streamlines, what is resulting in low pressure losses. It is also possible to achieve high tensile strength and stiffness of porous materials, in preferred embodiment as periodic cellular material; because of it turbo machine can operate at high rotational speeds and, consequently, reach high pressure differences and/or volume flows. Support structure of porous material is preferably made of metal or polymer. Material can be coupled with the lower and/or the upper wall, so that it forms a shape of panel or »sandwich structures With the appropriate technology is possible a large-scale production of material and consequently solution that is interesting for market.

The essential feature of the invented centrifugal turbo machine rotor is transfer of mechanically inputted work through the structure of porous material in increase of stagnation pressure and consequently increase of medium enthalpy.

In the preferred embodiment on figure 2 is as rotating structure used an open-cell porous aluminium material from manufacturer ERG materials with an average cell diameter of 2 mm and is as photograph shown in figure 3 On figure 3 is with an number 3.1 schematically shown the diameter of the pore and with 3.2 cell diameter of porous material. Mentioned material has proved sufficient mechanical strength and relatively low resistance to fluid flow. Mentioned material is homogeneous and isotropic. In the context of the invention is also possible usage of anisotropic and non-homogeneous material. Driven fluid is in this preferred embodiment air. Rotor 2.1 of centrifugal turbo machine, preferably driven by electric motor, is attached to the shaft 2.4 and consists of a porous material 2.6, preferably disc-shaped, hub or lower wall 2.3, upper wall 2.2, inducerja 2.5 and connection elements 2.7, which are preferably integrated in the lower wall or hub 2.3. The height of porous material can be varied depending of the diameter. Preferably is the maximal height of porous material at the location with the smallest radius in relation to the axis of the shaft 2.4. Optionally inducer 2.5 may be inserted in the center of rotor that provides pre rotation of the air and prevents the formation of vortices in inlet of rotor 2.1. Optionally may be on the stationary part of turbo machine inserted bladed or bladeless diffuser 2.8, which converts part of kinetic energy of air in to stagnation pressure. Inducer 2.5 can be integrated into the lower wall or hub 2.3 or upper wall 2.2.

Centrifugal turbo machine rotor, with the rotor lower wall, or hub, which is attached to the shaft of turbo machine, is characterized by the fact that the structure of porous or cellular material fills in the radial direction from rotation axis towards the periphery of the rotor, at least a part of the rotor and this preferably to the circumference of rotor, where driven fluid travels in the radial direction through a porous or cellular material. The structure of porous or cellular material is any homogeneous, non-homogeneous, isotropic or anisotropic microstructure and is composed of solid material, preferably of metal, polymer or ceramic, with the density of porous or cellular material preferably between 5% and 30% of the density of base solid material and the average cell diameter between 0.1 and 20 mm, preferably between 1 and 4 mm. The structure of porous or cellular material is made from at least one assembly part.

It is understood that an expert in this field based on knowledge of the above description, and description of the preferred embodiment designs different embodiment, particularly in terms of different industrial design or a different dimensions of rotor without circumventing the characteristics of the invention.

Turbo machine described in the invention has due to the absence of blades none of previously described weaknesses of turbo machinery with blades. There is no pressure difference on both sides of the blade, and thus one of the main noise generating mechanisms does not occur. When is it used together with the diffuser there is no "blade passing." phenomena. Also, flow recirculation and stagnation vortices are not present. Consequently, the high efficiency is achieved in a wider flow range, exit fluid flow is uniform, without pressure pulsations. Noise is broadband, without the occurrence of discrete frequencies. Turbo machine weakness is pressure loss and, as a consequence, decrease in efficiency and generation of turbulent noise, which is rising with the relative speed of fluid inside the porous material. Usage is preferably in the range of low and middle volume flows. Compared with Tesla's bladeless rotor it is possible to achieve good efficiency in a wider range of fluid volume flows and lower losses at the entrance and exit from rotor.

Potential applications are everywhere, where low noise level in the range of small and medium volume flows is significant. Metallic porous material (»metal foam«) is also used for filtration of dust and as a heat exchanger, because of it would be possible to implement these two functions in a single rotor: engine cooling and filtration of particles, which are present in the driven fluid.

Claims

1. Centrifugal turbo machine rotor, with the rotor lower wall, or hub, which is attached to the turbo machine shaft, characterised in that the structure of porous or cellular material fills in the radial direction from the axis of rotation towards the circumference at least a part of the rotor, and this preferably to the circumference of rotor, whereas the driven fluid travels in the radial direction through a porous or cellular material.

2. Rotor as claimed in claim 1, characterised in that the structure of the said porous or cellular material is of any homogeneous, non-homogeneous, isotropic or anisotropic microstructure.

3. Rotor as claimed in claim 1, characterised in that the said porous or cellular material consists of solid material, preferably of metal, polymer or ceramic, with the density of porous or cellular material preferably between 5% and 30% density of base solid material and the average diameter of cells between 0.1 and 20 mm, preferably between 1 and 4 mm.

4. Rotor as claimed in claim 1, characterised in that the structure of the said porous or cellular material is made of at least one assembly part.