By Hung Nguyen-Schäfer
Aero and Vibroacoustics of automobile Turbochargers is a subject regarding features from the operating fields of thermodynamics of turbomachinery, aerodynamics, rotordynamics, and noise propagation computation.
In this widely interdisciplinary topic, thermodynamicsof turbomachinery is used to layout the turbocharger and to figure out its working stipulations. Aerodynamics is required to check the compressor circulation dynamics and circulate instabilities of rotating stall and surge, which may produce growling and whining-type noises. Rotordynamics is important to check rotor unbalance and self-excited oil-whirl instabilities, which bring about whistling and incessant tone-type noises in rotating floating oil-film sort bearings. For the particular case of turbochargers utilizing ball bearings, a few high-order harmonic and put on noises additionally occur within the rotor working variety. finally, noise propagation computation, based on Lighthill’s analogy, is needed to enquire airborne noises produced through turbochargers in passenger vehicles.
The content material of this ebook is meant for complex undergraduates, graduates in mechanical engineering, study scientists and practising engineers who are looking to larger comprehend the interactions among those operating fields and the ensuing impression at the attention-grabbing subject of Aero and Vibroacoustics of automobile Turbochargers.
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Extra resources for Aero and Vibroacoustics of Automotive Turbochargers
31a) in the perturbed pressure becomes the LEE given in Eq. 29a). The acoustic propagation equation LEE of the average noise pressure p0 is written in the radial direction r. 0 o2 p0 c20 o 2 op r À ¼0 ð3:32Þ ot2 r 2 or or Substituting a new unknown variable m = p0 Ár into Eq. 32), one obtains the acoustic propagation equation LEE in the radial direction after a few arithmetic calculations. o2 ðmÞ o2 ðmÞ À c20 ¼0 2 ot or 2 ð3:33Þ The noise pressure in Eq. 33) can be written for the forward and backward propagating waves in the complex formulation m ¼ p0fw ðr; tÞ þ p0bw ðr; tÞ r A1 A2 ¼ ejxðtÀr=cÞ þ ejxðtþr=cÞ r r p0 ðr; tÞ ¼ ð3:34Þ where Ai is the integrating coefficients; x is the oscillation angular frequency; r is the noise transmitting distance.
Generally, there are three kinds of boundary conditions at the enclosed surface (S) for the Helmholtz equation: • Dirichlet boundary condition at the rigid surface op0 ¼ 0 ) p0ðSÞ ðra ; tÞ ¼ constant on ðSÞ ð3:44cÞ • Neumann boundary condition at the vibrating surface op0 ¼ Àjq0 x vðSÞ ðra ; tÞ on ðSÞ ð3:44dÞ • Robin boundary condition (also impedance BC for Sturm-Liouville problems) p0ðSÞ ðra ; tÞ op0 q x ; Z q0 c % 0 ¼ Àjq x 0 k Z on ðSÞ ð3:44eÞ where Z is the noise impedance of the acoustic field, as given in Eq.
1. To generate the LSB frequencies, one superimposes the excitation frequency f2 on (2f2 - f1) to obtain the second-order frequency (3f2 - f1) following the thin arrow, and superimposing f2 again on the second-order frequency to generate the 44 3 Acoustic Propagation Theory third-order frequency (4f2 - f1). Another way, following the dark arrow, one obtains the new high-order harmonic frequencies of 2f2 and 3f2 by adding f2 to itself and 2f2, respectively. In order to receive the third-order frequency (2f2 ?
Aero and Vibroacoustics of Automotive Turbochargers by Hung Nguyen-Schäfer