Due to a current trend of increasing rotational speed and power, the problem of tone noise and pressure pulsation in centrifugal ventilators becomes a more urgent issue. Often the level of tones determines noise characteristics; mainly these are at blade-passing frequencies (BPF). The broadband noise resulting from small-scale turbulent pressure pulsation and secondary flows is an important problem as well. Numerical studies of pressure pulsation in ventilators are undertaken using the method based on a representation of compressible medium non-stationary motion as a combination of acoustic and vortex modes. Comparisons of results on an air pump unit show good agreement between computation and experimental data within 2 -3 dB in the total amplitude and first BPF harmonics. © Institute of Noise Control Engineering

Computational results of 3D turbulent compressible gas flow in a single-nozzle ejector are compared with experimental data. Full Navier-Stokes equations and k-ε model of turbulence are used for mathematical model of gas flow. In computations the suction gas flow rate was determined and compared with experimental one. Two computational grids — coarse and fine are used to perform simulation. The fine grid is differ from coarse one by adaptation near the nozzle of active gas. Comparison of results carried out on coarse and fine grids shows that the accuracy of coarse grid is enough to get reliable results. Difference of computed and experimental results is less then 4% for the flow rate of passive gas. These results enable to make computational study of the multi-nozzle water-steam ejector. Condensation of steam is taken into account by introducing the equilibrium model of condensation. It is found that location of nozzles and its length are the important parameters of ejector influencing considerably its characteristics. The process of the condensation of water vapor significantly influences the work of ejector with an increase of the suction flow rate by a factor of 2.

A numerical method and software package was developed for designers and researchers in the field of vibration and noise problems in centrifugal ventilators. The numerical procedure is based on a representation of unsteady compressible liquid flow as a form of vortex (pseudo-sound) and acoustic mode superposition. It gives a possibility to determine absolute amplitudes of pressure pulsation in the ventilator casing induced by unsteady interaction between nonuniform flow outgoing from a centrifugal impeller volute tongue or diffuser vanes, so-called blade passing tones. Inupt data includes 2-D ventilator geometry and operation mode. Acoustic impedance boundary conditions can be defined with a circuit specification or by direct inlet and outlet specific complex impedance definition. It is possible to take into account local wall-specific complex impedance to study a coating effect on reduction of pressure pulsation. Output data represents: unsteady pressure map in the ventilator casing; amplitude distribution map for any selected harmonic; pressure versus time curves with accompanied spectrum information at any point selected by user; total vibration load vectors acting on the ventilator volute casing; and static pressure, velocity, and vorticity distribution in the centrifugal impeller. Validation of the software was completed on the centrifugal pump air model with more than 400 measuring points for two different radial gaps. The mismatch with experimental data is mostly 1.5–2.0 dB of unsteady pressure amplitude. Effects of radial clearance, number and form of impeller blades, exit and wall impedance are considered as well. The successful validation of the numerical method shows a good prospect in optimizing centrifugal ventilator geometry with improving vibration and noise characteristics at the draft stage and reducing refinement costs.

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The centrifugal pump of high specific speed with a diagonal type of impeller flow is studied experimentally and numerically. 2D and 3D numerical methods are used with applying acoustics -vortex equations.Increasing energetic parameters of centrifugal pumps requires a more complex geometry of the impeller and volute as one need to raise the specific speed of the pump to provide a higher efficiency value. The pump of higher specific speed has an impeller with curved blades and diagonal meridional section. The flow outgoing the impeller has an essential axial component of velocity. Thus the two dimensional approach will not give the accurate prediction of pressure pulsations in the volute casing. This is why the new 3-dimensional method has been elaborated for this task. The 3D computational results of pressure pulsation are compared with those obtained by 2Dcomputation Measurements show that in the beginning of volute, in the pseudo-sound zone, amplitude of Blade Passing Frequency (BPF) spectral component is higher than that at the pump outlet by an order of magnitude. 3-Dimensional analysis gives a good agreement with experimental data while 2D prediction underestimates the BPF amplitude in the beginning of volute.