Acoustics Sound

Aero and Vibroacoustics of Automotive Turbochargers by Hung Nguyen-Schäfer

By Hung Nguyen-Schäfer

Aero and Vibroacoustics of automobile Turbochargers is a subject concerning points from the operating fields of thermodynamics of turbomachinery, aerodynamics, rotordynamics, and noise propagation computation.

In this extensively interdisciplinary topic, thermodynamicsof turbomachinery is used to layout the turbocharger and to figure out its working stipulations. Aerodynamics is required to check the compressor stream dynamics and circulate instabilities of rotating stall and surge, that could produce growling and whining-type noises. Rotordynamics is important to review rotor unbalance and self-excited oil-whirl instabilities, which bring about whistling and incessant tone-type noises in rotating floating oil-film variety bearings. For the specific case of turbochargers utilizing ball bearings, a few high-order harmonic and put on noises additionally happen within the rotor working diversity. finally, noise propagation computation, based on Lighthill’s analogy, is needed to enquire airborne noises produced via turbochargers in passenger vehicles.

The content material of this publication is meant for complex undergraduates, graduates in mechanical engineering, examine scientists and working towards engineers who are looking to higher comprehend the interactions among those operating fields and the ensuing impression at the fascinating subject of Aero and Vibroacoustics of automobile Turbochargers.

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The envelop signal of the sideband given in Eq. 73) has a frequency of 2 fm since its period equals one-half of the period of the modulation signal, as shown in Fig. 11. 4 Frequency Modulations of Nonlinear Aeroacoustics Constant tone: Fig. 12 Noise sideband frequencies in Waterfall plot (courtesy BMTS) • The rectification term 12Zeà X 2 in Eq. 70); • Second-order harmonic frequencies of 2x1 and 2x2 with the amplitudes X12 and X22 in Eqs. 72); • Noise sideband frequencies modulated by the excitation frequencies of x1 and x2 have the amplitudes that are proportional to the term of Ze*X1X2.

Iðx; tÞ ¼ p0 ðx; tÞ vðx; tÞ where p0 (x,t) v(x,t) ð3:14aÞ is the noise pressure, as given in Eq. 1b); is the air particle velocity. The time-averaged noise intensity vector is given over the time period T. 1 Aeroacoustic Characteristics 21 The rms noise intensity amplitude is calculated from Eqs. 14a). 2 Irms ðxÞ ¼ 2 0 0 prms ðxÞ prms ðxÞ ¼ Z q0 c ð3:15Þ where p0 rms is the root mean square of the noise pressure vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi u ZT u u1 p0rms ðxÞ ¼ t p02 ðx; tÞdt T ð3:16Þ 0 (d) Noise power Noise power is defined by the sum of the noise intensity over the surface S surrounding the noise source.

54) is rewritten in Z Z Z r:ð/rp0 ÞdV À r/:rp0 dV þ / k2 p0 dV ¼ 0 V V ð3:55Þ V Applying Gauss divergence theorem to the control volume V, it is given by Z I 0 r:ð/rp ÞdV ¼ ð/rp0 Þ: n dS V S ¼ I / op0 dS ¼ Àjq0 x vSa on S Z ð3:56Þ / dS Sa Substituting Eq. 56) into Eq. 55), one obtains Z Z 0 2 0 ðr/:rp À k / p ÞdV ¼ Àjq0 x vSa / dS V ð3:57Þ Sa within the fluid velocity vSa on the radiating surface satisfies the Neumann boundary condition given in Eq. 44d).  j op0  : ð3:58Þ vSa ¼ q0 x on ðSa Þ The Rayleigh-Ritz method approaches the noise pressure p0 (e) in the finite element e = 1,…,Ne in the local coordinate system (n1, n2, n3) by a finite series expansion according to [1].

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