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3. Harmony softwareContents:Application domainHarmony softwareMain features of the new 32-bit interface

3.1 Application domain

The current versions of Harmony software package were developed for computational modelling of pressure pulsations at bladepassing frequencies (BPF).

Studies of centrifugal machines show that, as a rule, the discrete BPF component and its harmonics have maximum spectralamplitudes of pressure pulsations and noise under the rated operation mode. BPF is defined by the formula

Where

- Frequency of rotation, Hz

- Number of impeller blades

- Harmonic order.

Experience shows that the amplitudes of BPF pressure pulsations depend on several design factors - form, number and dispositionof blades of the impeller, configuration of the volute, radial gap between the impeller and volute tongue.

The amplification of pressure pulsations can happen due to matching of frequencies of oscillations with acoustic resonancefrequencies of both the outlet duct and the volute i.e. the working cavity. In machines (ventilators) the length of acoustic wavescan be comparable to the size of the casing and outlet volume. Therefore the variation of rotation speed, number of impeller bladescan substantially modify the amplitudes of pressure pulsations due to the resonance into the machine (ventilator) working cavity.The behavior of BPF amplitude in the outlet pipe may considerably depends on the exit impedance boundary condition.

In the table below, one can see a few very rough estimations of influence of various factors on pressure pulsation amplitude.

Possible tasks that can be solved with Harmony

Chapter 3

Factor Rough estimation of influence (dB)

Position of the point in the machine working cavity 15

Radial gap change from 4% to 7% (no resonance case) 6

Increasing rotation speed by 20% (no resonance case) 3

Specific impeller geometry change (no resonance case) 9

Relation of numbers of impeller and diffuser blades (resonance) 20

Damping coating in the conical diffuser 8

Outlet pipe acoustic impedance (resonance) 15

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Here are presented some possible tasks that could be solved with Harmony software in reducing experimental costs.

Pressure pulsations determination in various points of a machine volute casing and diffuser. Influence of flow rate. Influence of rotation speed. Influence of radial clearance. Influence of geometry of the impeller (number and shape of blades, intermediary short blades). Influence of the machine casing geometry. Effect of damping coating. Effect of the outlet duct impedance.

3.2 Harmony software

Harmony software are developing in 3 versions. All these versions have some common features, such as PC implementation underMS Windows and enable the user to predict the influence of the pump geometry and operation parameters on the pressurepulsation inside the pump cavity and in the connected hydraulic circuit. Computational procedure consists of 3 main steps ofcomputation:

1. Impeller flow analysis2. Incompressible liquid flow in a pump casing (volute -- bladed diffuser -- conical diffuser -- hydraulic circuit)3. Wave equation solution to obtain pressure pulsations

There are 3 main types of results of a computational experiment that enable a user to make a conclusion easily:

A. Instantaneous pressure mapB. Amplitude pressure map for a selected harmonic of BPFC. Pressure time variation curve in an arbitrary point accompanied with spectrum data

The interface includes other useful additional features:

Static Pressure map in impeller channels Velocity vector field representation for impeller flow Resulting dynamical force and moment acting on the the volute casing Interface for definition of impedance boundary conditions of outlet pipe Export to DXF and Matlab format Possibility to compute with arbitrary impedance of the inner wall (damping coating)

3.2.1. Version MK1

The first version of Harmony software treats a simple volute- geometry by using polar coordinates that are exponentiallytransformed to obtain a more dense finite-difference grid near the impeller exit. The interface code of this version is a 16-bitWindows application. By using version MK1 it has been obtained useful results in studying of the influence of radial gap, andimpeller geometry on amplitudes of BPF pressure pulsation.

3.2.2. Version MK2

The second version was developed for computation of a bladed diffuser geometry by using an arbitrary curvilinear coordinates.Interface code of this version is a full 32-bit Windows application. This version called MK2 has been used for computationalstudies on the effect of the relation of numbers of impeller and diffuser blades in a new pump design. This version uses the same


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procedure of step 1 as for the version MK1 to complete impeller flow computation.

3.2.3. Version MK3

This version is under development recently. The main advantage of this version is a possibility to take into account an influence ofthe volute or bladed diffuser on impeller flow parameters. It means the impeller flow is considered as a non-axisymmetric i.e. flowparameters in impeller channels depend on the impeller angular position relatively to the pump casing. Version MK3 will give alsoa possibility to compute a pump with simple volute geometry as well as a pump with bladed diffuser by using arbitrary body fittedcurvilinear mesh.

3.3 Main features of the new 32-bit interface.

The new interface of version MK2 and MK3 will accumulate all ergonomic achievements of version MK1 with efficiency of 32-bit coding under MS Windows 95 and NT operation systems.

3.3.1 Impeller flow computation. Step 1

Now version MK2 includes interface of the impeller flow that consists of input dialogs of impeller geometry (Fig. 3-2, Fig. 3-4),initial condition of impeller flow computation (Fig. 3-1) and pump operation mode (Fig. 3-5).

Fig. 3-1 Definition of initial conditions



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Fig. 3-2 Blade geometry correction

Fig. 3-3 Inlet impedance definition.



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and bladed diffuser on arbitrary curvilinear grid. The information concerning pump casing geometry can be transferred to thefirst step for asymmetrical impeller flow computation. Full interface screen of the step 2 is shown on the Fig. 3-7.

Fig. 3-7 Full interface screen of the 2 step.

3.3.3 Wave equation solution. Step 3.

Interface of step 3 for the version MK2 has been developed during last year in wich all previous possibilities of version MK1 arekept and united with advantages of 32-bit application.



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Fig. 3-8 Full interface screen of the 3 step.

Send mail to [email protected] with questions or comments about this web site.Copyright 1999 Intellectual Reserves International, LtdLast modified: 08/31/99

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