TMF Design Optimisation for Automotive Turbochargers Turbine Housings

Abstract

Turbine housings for automotive turbochargers are complex castings that are subjected to transient thermal stress from exhaust gas temperature and flow variation under complex duty cycles. A fatigue model based on a cumulative damage approach (Chaboche model [1]) is used to predict crack initiation. As the stress varies with temperature, a modified Chaboche model based on a normalized stress is proposed. To determine the transient stress and temperature distributions due to the high rates of convection from the gas, and the complexity of the design, conjugate heat transfer CFD simulation is performed. The tongue of the turbine housing is a critical region in which cracks initiate within a short time. Heat transfer coefficients ( HTC ) and bulk temperature predictions from CFD, in general, can be validated by thermal measurement. But because of the geometry and the location of the tongue, it is impossible to measure the metal temperature. For this work 2 methods were presented: HTC calibrated by thermal measurement and HTC from CFD heat transfer Conjugate method, steady state analysis. Heat transfer Coefficients and bulk temperatures obtained with those 2 methods are different. The heat transfer from CFD analysis with 15 layers has an important HTC which is 3000 W/ m2 °C, it is equal to 1200 W/m2 °C for the calibrated method, but the bulk temperatures are not the same. A sensitivity study on predicted life shows that this difference results in no more than a 2 hr change for a total predicted life of 50 hrs. In the industrial approach this difference is quite acceptable. The design of a turbine housing is optimized based on this TMF methodology and shows very good results in testing, as presented here.

A review of heat transfer in turbochargers

“…However, the universal tensile strength of the material decreased at higher temperature, thus reducing the maximum pressure ratio from 4.6 to 4.2 [33]. Ahdad et al [61] performed a fatigue analysis on turbine housing under transient conditions and observed tensile and compressive stress in the cooling and heating phase respectively. The accuracy of the structural analysis is improved in the transient analysis as the observation of stress during the cooling and heating process is vital.…”

“…The accuracy of the structural analysis is improved in the transient analysis as the observation of stress during the cooling and heating process is vital. In the turbine housing, the tongue and divider wall are subjected to the maximum thermal stress [61,29]. Ahdad et al [61] noticed a crack in the divider wall after 300 cycles (50 hours).…”

“…In the turbine housing, the tongue and divider wall are subjected to the maximum thermal stress [61,29]. Ahdad et al [61] noticed a crack in the divider wall after 300 cycles (50 hours). Heuer et al [29] analyzed the turbine housing with knobs acting as cooling fins, and observed that it helped to distort the thermal distribution in divider walls.…”

Experimental and numerical investigation of the thermomechanical load on a turbine housing in a radial turbocharger

“…Turbine housing -a key part of the turbocharger -generates thermomechanical fatigue under the influence of high-temperature gas and engine vibrations. [1][2][3] Hence, the thermomechanical fatigue of turbochargers has become a concern in the design of turbochargers.…”

“…8,10 The thermomechanical fatigue life of a component can be evaluated by solving the thermomechanical temperature and stress of the part. Thermomechanical temperature and strain (stress) simulations are solved by uncoupled or coupled methods; the uncoupled method requires manual control of iteration errors and the assessment of convergence results; it only focuses on the relationship between the core physical quantities in the physical field 2,8,11 The coupling solution can set the iteration error and automatically obtain the convergence result; we focus on the relationship between multiple or all physical quantities in the physical field. [12][13][14] The temperature field measurement of the turbocharger components requires a thermocouple to acquire the temperature at a point on the measured object.…”