By Hung Nguyen-Schäfer
Aero and Vibroacoustics of car Turbochargers is a subject regarding points from the operating fields of thermodynamics of turbomachinery, aerodynamics, rotordynamics, and noise propagation computation.
In this largely 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, which 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 relentless tone-type noises in rotating floating oil-film style bearings. For the specified 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 booklet is meant for complicated undergraduates, graduates in mechanical engineering, learn scientists and training engineers who are looking to larger comprehend the interactions among those operating fields and the ensuing impression at the fascinating subject of Aero and Vibroacoustics of car Turbochargers.
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Additional info for Aero and Vibroacoustics of Automotive Turbochargers
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. I P ¼ I:n dS ð3:17Þ S The time-averaged noise power is resulted from the time-averaged noise intensity and surrounding surface.
Due to high rotational speed of the CW, the intake air pressure is increased at the blade outlet 2. The charge air pressure is Fig. 1 Aerodynamic Noise 49 additionally gained in the diffuser built in the compressor housing between the CW and the volute. The charge air mass flow rate through the compressor, not the charge air pressure, is used for turbocharging downsized engines. The compressor torque is derived from the angular momentum equation. M C ¼ m_ C ðr2 cu;2 À r1 cu;1 Þ ð4:1aÞ where m_ C is the compressor mass flow rate; r1 and r2 are the inlet (inducer) and outlet (exducer) radii of CW; cu,1 and cu,2 are the tangential (or whirl) velocities at the inlet and outlet.
6 Flow velocity profiles in a radial compressor wheel where ht,1, ht,2 cp c total enthalpies at the CW inlet and outlet (see Appendix A); air heat capacity at constant pressure; absolute air velocity. In the case of the backward swept CW mostly used in automotive turbochargers, the charge air is compressed on the impeller front face in the rotating direction x, which is called the pressure side (ps = ? + +), as indicated in Fig. 6a. On the contrary, the airflow separates from the impeller back face near the outlet 2, which is called the suction side (ss = - - -) opposite to the pressure side.