Lumped Capacitance and Three-Dimensional Computational Fluid Dynamics Conjugate Heat Transfer Modeling of an Automotive Turbocharger

Abstract

One-dimensional wave-action engine models have become an essential tool within engine development including stages of component selection, understanding system interactions, and control strategy development. Simple turbocharger models are seen as a weak link in the accuracy of these simulation tools, and advanced models have been proposed to account for phenomena including heat transfer. In order to run within a full engine code, these models are necessarily simple in structure yet are required to describe a highly complex 3D problem. This paper aims to assess the validity of one of the key assumptions in simple heat transfer models, namely, that the heat transfer between the compressor casing and intake air occurs only after the compression process. Initially, a sensitivity study was conducted on a simple lumped capacity thermal model of a turbocharger. A new partition parameter was introduced αA, which divides the internal wetted area of the compressor housing into pre- and postcompression. The sensitivity of heat fluxes to αA was quantified with respect to the sensitivity to turbine inlet temperature (TIT). At low speeds, the TIT was the dominant effect on compressor efficiency, whereas at high speed αA had a similar influence to TIT. However, modeling of the conduction within the compressor housing using an additional thermal resistance caused changes in heat flows of less than 10%. Three-dimensional computational fluid dynamics (CFD) analysis was undertaken using a number of cases approximating different values of αA. It was seen that when considering a case similar to αA = 0, meaning that heat transfer on the compressor side is considered to occur only after the compression process, significant temperature could build up in the impeller area of the compressor housing, indicating the importance of the precompression heat path. The 3D simulation was used to estimate a realistic value for αA which was suggested to be between 0.15 and 0.3. Using a value of this magnitude in the lumped capacitance model showed that at low speed there would be less than 1% point effect on apparent efficiency which would be negligible compared to the 8% point seen as a result of TIT. In contrast, at high speeds, the impact of αA was similar to that of TIT, both leading to approximately 1% point apparent efficiency error.

Experimental validation of a quasi-two-dimensional radial turbine model

“…Such is the case of the heat transfer effects, that can be determined experimentally with a simple lumped model as in 9 or 10 . The simplifications that are used in simple turbocharger heat transfer models that are coupled with one-dimensional gas dynamics codes have been validated both experimentally and with computational fluid dynamics (CFD) simulations, as in 11 . The results of including a heat transfer model to determine internal heat flows has been investigated by several authors, such as in the works by Olmeda et al 12 or Serrano et al 13 .…”

“…8 Other aspects of the turbocharger behaviour can be taken into account in these simulations. Such is the case of the heat transfer effects, which can be determined experimentally with a simple lumped model as in Bohn et al 9 or Serrano et al 10 The simplifications that are used in simple turbocharger heat transfer models that are coupled with 1D gas dynamics codes have been validated both experimentally and with computational fluid dynamics (CFD) simulations, as in Burke et al 11 The results of including a heat transfer model to determine internal heat flows has been investigated by several authors, such as in the works by Olmeda et al 12 or Serrano et al 13 These models can even be used to obtain information that is difficult to measure in an experiment, such as the difference in heat flow paths, as in the work by Aghaali et al 14 Friction losses models as the one developed by Serrano et al 15 or Marelli et al 16 have been also coupled with 1D gas dynamics codes so the mechanical efficiency can be computed in time marching simulations, as shown in Serrano et al 17 Several works about radial turbine modelling can be found in the literature, where the properties of the internal flow of the turbine under different boundary conditions are presented and discussed, as can be seen in the works by Galindo and Colleagues 18,19 and Hakeem et al 20 Especially focused in the unsteady performance at high frequencies are the works by Hu 21 and King. 22 Also, the experimental characterisation of turbochargers increases in complexity in parallel to the models that use this information.…”

A review of heat transfer in turbochargers

“…The assumptions made in lumped capacitance models or other 1-D models should be validated in order to have a basis. This validation could be done by conducting focused experiments or 3-D CHT model [34]. Such validation is essential in strengthening the many results found in the literature which are generated by 1-D models.…”

“…The temperature distribution obtained from the CHT method is used for the structural analysis using the finite element method (FEM) to determine the thermal stress/strain of turbocharger parts under thermal load [33]. Increasing number of researches on heat transport in turbochargers is studied through CHT [34,35]. Individual components such as turbine, compressor and bearing housing along with full turbocharger analyses are also done using CHT [35,36].…”

Boosting the Capabilities of Gas Stand Data Acquisition and Control Systems by Using a Digital Twin Based on a Holistic Turbocharger Model

“…During the last decades, increasingly advanced turbocharger models have been developed for sizing, engine matching and one-dimensional modeling [4]. All the interesting phenomena are currently considered with high accuracy: adiabatic map extrapolation of both turbine [4] and compressor [5], friction losses [6] and heat transfer effects [7], can be computed hundreds of times per second with commodity hardware. All of these sub-models are based on zero-or onedimensional approaches and are used in a whole engine model simulation to improve the predictions [8].…”