Conjugate Heat Transfer Calculations Research Articles

Numerical study on conjugate heat transfer in a liquid-metal-cooled pipe based on a four-equation turbulent heat transfer model

Conjugate heat transfer between liquid metal and solid is a common phenomenon in a liquid-metal-cooled fast reactor's fuel assembly and heat exchanger, dramatically affecting the reactor’s safety and economy. Therefore, comprehensively studying the sophisticated conjugate heat transfer in a liquid-metal-cooled fast reactor is profound. However, it has been evidenced that the traditional Simple Gradient Diffusion Hypothesis (SGDH), assuming a constant turbulent Prandtl number (Prt, usually 0.85 - 1.0), is inappropriate in the Computational Fluid Dynamics (CFD) simulations of liquid metal. In recent decades, numerous studies have been performed on the four-equation model, which is expected to improve the precision of liquid metal’s CFD simulations but has not been introduced into the conjugate heat transfer calculation between liquid metal and solid. Consequently, a four-equation model, consisting of the Abe k−ε turbulence model and the Manservisi kθ−εθ heat transfer model, is applied to study the conjugate heat transfer concerning liquid metal in the present work. To verify the numerical validity of the four-equation model used in the conjugate heat transfer simulations, we reproduce Johnson’s experiments of the liquid lead-bismuth-cooled turbulent pipe flow using the four-equation model and the traditional SGDH model. The simulation results obtained with different models are compared with the available experimental data, revealing that the relative errors of the local Nusselt number and mean heat transfer coefficient obtained with the four-equation model are considerably reduced compared with the SGDH model. Then, the thermal-hydraulic characteristics of liquid metal turbulent pipe flow obtained with the four-equation model are analyzed. Moreover, the impact of the turbulence model used in the four-equation model on overall simulation performance is investigated. At last, the effectiveness of the four-equation model in the CFD simulations of liquid sodium conjugate heat transfer is assessed. This paper mainly proves that it is feasible to use the four-equation model in the study of liquid metal conjugate heat transfer and provides a reference for the research of conjugate heat transfer in a liquid-metal-cooled fast reactor.

The development of multi-physics approach with Monte Carlo and computational fluid dynamics coupling for reactor cores

Highly accurate solutions for neutronic and thermal hydraulic phenomena in reactor cores certainly improve the safety conclusions about the reactors. The coupling methodology of governing physics of these two fields by using Monte Carlo and computational fluid dynamics (CFD) methods was described in this study with its application to Istanbul Technical University (ITU) TRIGA Mark II Research Reactor. As a different approach, instead of not modelling top and bottom grid plates of the reactor that is the common practice for geometrical simplification, the effect of grid plates on flow hydrodynamics was included into the conjugate heat transfer calculations as boundary conditions. The investigation on the effect of core element temperature, cross sections, and S(α,β) thermal scattering data showed the need of proper coupling of neutronic and thermal hydraulic fields since 30–45% relative error on excess reactivity value of the ITU research reactor was observed. With the developed loose coupling model, 483 individual cross section and 483 different S(α,β) thermal scattering data were generated by using NJOY nuclear data generation code and MAKSXF and OTF utilization tools of MCNP6.2 code. The reactivity loss against power increase in research reactor value of this study showed 6% relative error with loose coupling comparing to maximum 50% without coupling.

A computational conjugate heat transfer study of a rectangular minichannel undergoing sinusoidal flow pulsations

The development of current and next generation high performance electronic devices has led to smaller components in more densely packed spaces. The increasing power levels have resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling systems is viewed as a potential solution to the problems involving high heat flux densities. A review of published literature indicates a lack of time-resolved and space-resolved links between the hydrodynamic pulsating characteristics and associated heat transfer perturbations. The scope of this work involves the development of a validated three-dimensional conjugate heat transfer computational model to investigate hydrodynamically and thermally fully developed pulsating flows in a heated rectangular minichannel. Simulations were performed for a sinusoidal waveform with a fixed pulsation amplitude for varying pulsation frequencies in the range of 0.02 Hz to 25 Hz, corresponding to Womersley numbers in the range of 0.5 ≤Wo≤ 18.33. Low pulsation frequencies exhibited the well known parabolic profile for the fluctuating hydrodynamic and thermal parameters, i.e., velocity, wall shear, and wall temperature. As a result, the axial pressure gradient, velocity, and wall shear stress profiles were in phase and similar results were obtained for the oscillating wall and bulk fluid temperatures. For the inertia dominated high frequency flows, an increase in axial pressure gradient leads to a phase lag of π/2 when compared with the velocity and wall shear profiles. The shorter time period pulsations exhibit unique attributes in the form of flow reversal effects at local near wall regions. High near wall thermal gradients were observed as a result of stronger viscous effects due to a narrowing thermal boundary layer; consequently the transverse diffusion of heat was ineffective. A phase lag and a subsequent drop in the peak magnitudes existed between the oscillating bulk and wall temperatures for high frequency flows. Fluctuations in near wall heat flux profiles showed a dependency on the imposed pulsation frequencies. For the chosen pulsation profile and frequencies, the overall time averaged thermal performance indicates that pulsating flow performs worse than steady flow for a flow rate amplitude of 1. The highest thermal performance was achieved for Wo=5.1 while maintaining a low friction factor.

The Effect of Single-Sided Ribs on Heat Transfer and Pressure Drop Within a Trailing Edge Internal Channel of a Gas Turbine Blade

Abstract Convective cooling in a gas turbine blade internal trailing edge channel is often insufficient at the sharp trailing edge. This study examines convective heat transfer and pressure drop within a simplified nonrotating trailing edge channel. The internal passage has been modeled as a right triangular channel with a 9 deg angle sharp corner. A copper plate was heated from underneath via a uniform heat flux heater and examined via infrared thermography for two cases: smooth wall and single-sided ribbed wall. Nonuniformity in the heat flux due to conduction is corrected by a Reynolds-averaged Navier–Stokes (RANS) conjugate heat transfer calculation, which was validated by the mean velocity, friction factor, and temperature fields from experiments and large eddy simulation (LES). Nusselt number distributions illustrate that surface heat transfer is increased considerably with ribs and coupled with the vortices in the flow. Heat transfer at the sharp corner is increased by more than twofold due to ribs placed at the center of the channel due to secondary flow. The present single-sided ribbed channel utilizes secondary flow toward the corner and is presumed to have better thermal performance than a dual-sided ribbed channel. Thus, it is important to set the appropriate rib length within the channel.

Conjugate heat transfer simulation of sulfuric acid condensation in a large two-stroke marine engine - the effect of thermal initial condition

In the present study, conjugate heat transfer (CHT) calculations are applied in a computational fluid dynamics (CFD) simulation to simultaneously solve the in-cylinder gas phase dynamics and the temperature field within the liner of the engine. The effects of different initial temperatures with linear profiles across the liner are investigated on the wall heat transfer as well as on the sulfuric acid formation and condensation. The temporal and spatial behavior of sulfuric acid condensation on the liner suggests the importance of CHT calculations under large two-stroke marine engine relevant conditions. Comparing the mean value of the heat transfer through the inner and outer sides of the liner, an initial temperature difference of 15 K with a linear profile is an appropriate initial condition to initiate the temperature within the liner. Moreover, the effect of the amount of water vapor in the air on the sulfuric acid formation and condensation is studied. The current results show that the sulfuric acid vapor formation is more sensitive to the variation of the water vapor amount than the sulfuric acid condensation.

Steady-State Fluid-Solid Mixing Plane to Replace Transient Conjugate Heat Transfer Computations during Design Phase

The demand for increased turbomachinery performance, both, towards higher pressures and temperatures, leads to high thermal-loads of specific components and can critically affect mechanical integrity. In the particular case of rotating-disk configurations, like the back-side of wheels or in cavities, a very efficient way for cooling is jet impingement. An example for this situation are high pressure-ratio turbochargers, where cooling of the impeller disk (back wall) is introduced to achieve tolerable thermal loads. From the physical point of view, jet impingement on a rotating wall generates an unsteady heat transfer situation. On the other end, accurate values of time-averaged temperatures would be sufficient for design purposes. In general, obtaining circumferentially time-averaged solutions requires transient analysis of the conjugate heat transfer (CHT) process to account for the mean effect of jet cooling on solids. Such analysis is computationally expensive, due to the difference in information propagation time-scale for the solid and the fluid. In this paper, a new approach to directly compute circumferentially time-averaged (i.e., steady-state) temperature distributions for rotating-disk CHT problems is presented based on an adaption of the well known fluid-fluid mixing plane approach.

Some Observations on the Computational Sensitivity of Rotating Cavity Flows

Abstract Across the open literature, there is no clear consensus on what the most suitable modeling fidelity is for rotating cavity flows. Although it is a widely held opinion that unsteady Reynolds-averaged-Navier–Stokes (URANS) approaches are unsuitable, many authors have succeeded in getting reasonable heat transfer results with them. There is also a lack of research into the validity of hybrid URANS/large eddy simulation (LES) type approaches such as detached eddy simulation (DES). This paper addresses these research challenges with a systematic investigation of a rotating cavity with axial throughflow at Grashof numbers of 3.03×109 and 3.03×1011. The disk near-wall layers remained laminar at both conditions, meaning that a turbulence model should not be active in these regions. The disk heat transfer was observed to affect the near-disk aerodynamics, which in turn affect the disk heat transfer: this feedback loop implies that conjugate heat transfer computations of rotating cavities may be worth investigating. On the shroud, additional eddy viscosity in URANS and DES was found to interfere with the formation of heat transfer enhancing streaks, whilst these were always captured by LES. DES exhibited a concerning behavior at the higher Grashof number. Locally generated eddy viscosity from the shroud was injected into the bulk fluid by the radial inflow. This contaminated the entire cavity with nonphysical modeled turbulence. As the radial inflow is a characteristic feature of rotating cavity flows, these results show that caution is necessary when applying hybrid URANS/LES approaches to this type of flow.

A high temperature turbine blade heat transfer multilevel design platform

In this work, a fast and efficiently design method has been introduced. This design process consists of the overall design and the detailed design. For the overall design, one-dimensional pipe-network computations are employed to obtain several design cases quickly at the beginning. Meanwhile the solid domain geometry and mesh with cooling structures, i.e., film holes, impingement holes, and ribs have been generated to carry out three-dimensional (3-D) heat conduction calculations. Based on the above, a detailed design has been performed by 3-D conjugate heat transfer calculations. The results show that both the average temperature and the mass flow maximum errors between the pipe-network and 3-D conjugate heat transfer calculations are about 10%. In this article, the cooling structure of a gas turbine blade is designed with this platform. The final design results show that the maximum dimensionless temperature on the blade surface is 0.813, i.e., lower than the design requirement. The dimensionless mass flow rate in the first cooling inlet is 0.0168, and the mass flow rate in the secondary inlet is 0.0231.

Numerical approach to define a thermodynamically equivalent material for the conjugate heat transfer simulation of very thin coating layers

The 3D Conjugate Heat transfer (CHT) calculation of the heat transfer from the gas to the walls of a combustion chamber requires very fine meshing, particularly so when the walls are coated with a very thin insulation layer. It is practically impossible to mesh such thin layers for numerical as well as computational cost reasons. In this paper a solution to this problem is presented: an equivalent material layer with a reasonable meshing thickness is defined in such a way that its thermal behavior matches that of the real very thin coating layer. The methodology used to define the thermodynamic properties of the equivalent coating material is based on a combination of a 1D heat transfer model and a multi-factorial sweep of material properties. This equivalent material layer can then be introduced in the 3D CHT calculation instead of the real coating thin layer, and can be adequately meshed to predict with accuracy the heat losses. The approach is illustrated for a real case and a parametric study is performed to evaluate the importance of the number of mesh nodes and the material thickness.

Large-Eddy Simulation of a Model Aero-Engine Sooting Flame With a Multiphysics Approach

In this work, an in-house developed multiphysics unsteady approach (U-THERM3D) is employed to compute wall temperatures in a loosely coupled manner for a model aero-engine combustor, fueled with a non-premixed ethylene/air mixture and representative of the RQL technology. Large-Eddy Simulation (LES) is carried out to prove that scale-resolving approaches are required for a reliable prediction of turbulent mixing with respect to steady-state methods. A Flamelet Generated Manifold approach is adopted to describe the reactive flow, whereas two additional transport equations are included to predict the soot concentration. For a thorough investigation of the considered aero-engine combustor, cold flow results are firstly presented, highlighting the importance of an accurate predictions of general flow features. Then, the aerothermal fields are analysed to show the overall accuracy of the developed approach and so the impact of heat losses, comparing the results of an adiabatic simulation with respect to the loosely coupled conjugate heat transfer calculation. Finally, the investigation is focused on the prediction of the wall temperature distribution to prove the advantages of the U-THERM3D procedure with respect to steady-state approach.

Reactivity Feedback Effect on Supercritical Transient Analysis of Fuel Debris

Transient analysis for possible prompt supercritical accidents of fuel debris in the Fukushima Daiichi Nuclear Power Station is quite important. However, unlike solution fuel systems, there is little knowledge about supercritical transient analysis in fuel debris systems. In particular, reactivity feedback effects, which may have a significant impact on the results of the analysis, are important and require further study. In particular, the impacts of radiolysis gas void and moderator boiling should be discussed. Thus, the purpose of this study is to clarify whether the reactivity feedback effects of radiolysis gas and boiling of the moderator impact the supercritical transient analysis in fuel debris systems. To accomplish this, we used a power profile obtained by the MIK code with the Doppler reactivity feedback effect; radiolysis gas analysis and heat transfer analysis were performed. For the radiolysis gas analysis, the AGNES2 model was modified to consider the difference between solution fuel and fuel debris systems. The heat transfer analysis used an OpenFOAM solver to perform conjugate heat transfer calculations. We found that the radiolysis gas void was negligible when probable G values, which are the generation number of molecules per absorbed energy, were used. In addition, the results showed that boiling could be also negligible under most conditions. However, we found that the boiling time may be earlier than the peak time of the power when the radius of the fuel debris particle is small. In this case, ignoring the boiling may give conservative results. These considerations should be included in future analyses.

The investigations of slot film outflow used on the laminated cooling configuration

The discrete film hole is the most common form of film cooling configurations in the turbine vane and blade. To enhance the film cooling effect, the improved hole, such as expanding-shape hole, is being used to replace the traditional cylindrical hole in the vane and blade cooling design. However the slot film outflow is been seen as the best form of film cooling when compared to the discrete holes. The slot film cooling configuration is usually used in the trailing edge of turbine vane and blade, but cannot be used in the mid-body of turbine vane and blade, with be drawback of lower mechanical strength. The present paper used the slot film outflow on the laminated cooling configuration. With the ribs in the laminated cooling configuration, the novel configuration can remarkably overcome the mechanical drawback of the simple slot film cooling, and can enhance the film cooling effect of the laminated cooling configuration. To investigate the cooling effect of laminated configuration with slot film outflow, four kinds of specimens are designed, including the traditional design with discrete film hole (baseline), the rearrangement design with discrete film hole (case A), the novel design with discrete slot (case B), and the novel design with continuous slot (case C). The Conjugate heat transfer (CHT) computations and the Pressure Sensitive Paint (PSP) test methods are used to assess the overall cooling performance (ηoverall) and the adiabatic film cooling effectiveness (ηfilm). The results show the two slot design cases (case B and case C) have higher film cooling effectiveness with more covered surface areas of film outflow, while performs lower flow resistance due to the lower flow velocity of the coolants in the slot. With the increase of Br, the film cooling effectiveness of two slot design cases (case B and case C) can keep increase, but the two hole design case (baseline and case A) cannot increase at area of Br > 0.55. At the blowing ratio near 0.96, for the baseline case, case A, case B, and case C, the area-averaged film cooling effectiveness is 0.26, 0.20, 0.68, and 0.50 respectively; and area-averaged the overall cooling effectiveness is 0.72, 0.81, 0.89, and 0.85 respectively; the flow frictions coefficients is 1.78, 2.15, 1.37, and 2.01 respectively.

Multi-objective optimization of discrete film hole arrangement on a high pressure turbine end-wall with conjugate heat transfer simulations

This paper discussed a method of combining a full automatic multi-objective optimization and conjugate heat transfer calculation to obtain optimal cooling layouts on a transonic high pressure guide vane under a realistic turbine working condition. The improvement in cooling design from the optimized models was analyzed in detail, along with a discussion of sensitivities of two objective functions to five design variables. The full automatic method comprises the process of geometry creation, mesh generation, numerical solution and post data analysis. The vane is solid and the end-wall is arranged in a linear cascade. On the end-wall, film holes are all cylindrical and classified in five regions, with region A near the leading edge of the vane, region B near the suction side, regions C and D near the pressure side, and region E for the rest. Five design variables are three pitch-to-hole ratios in regions B, D, E and two compound angles of film holes in regions A and D. Two selected objective functions are area averaged overall cooling effectiveness of the end-wall and aerodynamic losses in a cross-plane at x/Cax = 1.06 just downstream of the outlet of the cascade. For the optimization process, the multi-objective genetic algorithm based on the Non-dominated Sorted Genetic Algorithm-II was applied. The Latin hypercube sampling method was used to choose 21 experimental design points in the design space, which are also the sources for constructing the surrogate models with the Kriging model. The results demonstrate that the method using full automatic optimization and conjugate heat transfer calculation has achieved an increase of 8.7%–9.5% in area-averaged overall cooling effectiveness and a reduction of about 4.8%–6.1% in aerodynamic losses. The highest increase in cooling effectiveness exists in the region near the pressure side with a mild increase in the middle of the passage. The largest heat flux reduction exists in the regions near the pressure side and the crown of the suction side. The change of compound angle in region A near the leading edge has a negligible influence on overall cooling effectiveness but a high impact on aerodynamic losses. It's advisable to maintain the compound angle and pitch-to-diameter ratio at low values in region D near the pressure side to obtain high cooling performance.

New approach to study the heat transfer in internal combustion engines by 3D modelling

The stringent environmental constraints have led the industry to look for new technologies that improve the design of internal combustion engines (ICE), mainly focused on achieving higher thermal efficiency and reducing pollutant emissions. Numerical simulations play a key role for optimizing engine design, but modelling the physical processes such as the combustion and the heat transfer to the walls, represents a challenge due to the complexity of the phenomena involved. Combustion has to be modeled properly, and heat transfer models from gas to wall require coupling with solid wall models (CHT Conjugate Heat Transfer calculations). In this paper, a new approach is presented, focused on optimizing the computing time needed to perform CHT simulations. It is based on the use of the Rate of Heat Release (RoHR) obtained from a CFD calculation to replace the combustion process. The study is performed for a spark ignition (SI) engine. The proposed approach is validated for the heat transfer to the piston wall. The study shows that the CHT-RoHR approach yields very good results in terms of spatially averaged values during the whole engine cycle and allows considerable reduction in computational cost. It is therefore very useful to perform parametric studies.

Numerical stress analysis of the TBC-film cooling system under operating conditions considering the effects of thermal gradient and TGO growth

Strength assessment of the thermal barrier coating (TBC)-film cooling system plays a significant role in the safety design of gas turbine blades. In this work, a numerical study of the thermal-mechanical behavior of the TBC-film cooling system under operating conditions was conducted. The temperature field of the system was obtained using conjugate heat transfer calculation, and the effect of radiation heat transfer was considered. Subsequently, finite element calculations were performed for stress analysis during both high-temperature exposure and a cooling-down period after 500 h creep and oxidation. The results showed that film cooling brought about a steep thermal gradient and the uneven growth of thermally grown oxide (TGO). High stress concentration appeared around the cooling hole. In addition, interfacial peeling stress and shear stress were generated at the hole edge, which might induce Mode I and Mode II edge crack initiation in TBC upon heating or cooling, respectively.

Surface temperature reduction by using dimples/protrusions in a realistic turbine blade trailing edge

In this article, numerical simulations have been conducted on the heat transfer effect of dimple/protrusion layouts of a pin-finned wedge duct. Conjugate heat transfer calculations are further performed to investigate the cooling effect of modified schemes with dimples and protrusions added. Comparisons are carried out with a turbine second stage guide vane employed as the prototype. The dimple/protrusion-pin fin arrangement is set as the optimum one obtained above, and dimple depth/protrusion height varies from 0.2 to 0.3 times the structure diameter. It is found that the side-by-side arrangement and protrusion structure is more beneficial for the wedge duct endwall heat transfer. Comparison with the prototype blade shows that the addition of both dimples and protrusions are helpful in enhancing the trailing edge cooling effect. The cooling effect is increased with an increase in dimple depth/protrusion height. The results also show that the modified blade with protrusions attached at 0.3 height saves 0.48 g/s cooling mass flow and reaches the most positive performance with a 17 K, 14 K average temperature reduction, 0.022, 0.018 cooling effect increasing for pressure, suction side, respectively.

Low order modeling method for assessing the temperature of multi-perforated plates

A low-order model is proposed to predict the temperature of a multi-perforated plate from an unresolved adiabatic computation. Its development relies on the analysis of both an adiabatic and a conjugate heat transfer wall resolved large eddy simulation of an academic multi-perforated liner representative of the cooling systems used in combustion chambers of actual aero-engines. These two simulations show that the time averaged velocity field is marginally modified by the coupling with the heat diffusion in the perforated plate when compared to the adiabatic case. This gives rise to a methodology to assess the wall temperature from an unresolved adiabatic computation. It relies on heat transfer coefficients from referenced correlations as well as a mixing temperature relevant to the flow in the injection region where the cold micro-jets mix with the hot outer flow. In this approach, a coarse mesh simulation using an homogeneous adiabatic model for the aerodynamics of the flow with effusion is post-processed to provide a low cost alternative to conjugate heat transfer computations based on hole resolved meshes. The model is validated on an academic test case and successfully applied to a real industrial combustion chamber.

Numerical prediction of heat loss from a test ribbed rectangular channel using the conjugate calculations

Conjugate heat transfer of air and steam in a rectangular channel with 90° ribs along two opposite walls was investigated experimentally and numerically. The stainless steel test section was 80 mm × 40 mm × 2.5 mm and the ribs were 80 mm × 2.5 mm × 2.5 mm with 25 mm between ribs. The tests investigated the effects of coolant mass flow rate (the corresponding Reynolds numbers in the range of 10,000-50,000) on the conjugate heat transfer enhancement with the ribs. Two conjugate heat transfer calculation methods with different models were developed. For the first model (CHT-Q model) solid domain was viewed as a uniform internal heat source with the adiabatic exterior surfaces, while for the second model (CHT-T model) the outwall temperature was specified by the fitting polynomials of measured data with the zero internal heat. Comparisons between the experimental and numerical results showed that the SST k–ω turbulence model was more suitable for the conjugate heat transfer in such channels. Regardless of numerical error, an approximation of heat loss was specified by the successive trial calculations of the CHT-Q model, while a relatively accurate heat loss was evaluated by the post-processing of the CHT-T calculation. Local heat transfer coefficient can be determined accurately by the quantified heat loss of test system. The critical impact of conjugate heat transfer was demonstrated. Furthermore, the steam coolant compared to air exhibited a higher heat transfer performance by 12–25% for both the ribbed and smooth walls at the same Reynolds number.

Computational Conjugate Heat Transfer Analysis of a Hybrid Electric Vehicle Inverter

ABSTRACTA physics-based computational simulation of the heat transfer characteristics of an insulated gate bipolar transistor (IGBT) developmental inverter is reported. The simulation considers the fluid/thermal multiphysics interactions via a conjugate heat transfer analysis. The fluid phase includes air and liquid coolant; the solid phase, where the heat is conducted, includes various solid materials. Numerical solutions of the heat conduction and convection phenomena in and around the IGBT modules and the inverter, built as a three-dimensional computational model, are sought for by using parallel computing. Comparisons with the available experimental data show a satisfactory agreement of the inverter temperature at three power levels under two different coolant flow rates. Detailed examination of the flow field reveals that the design features of the rectangular coolant flow chamber in the heat sink and the small clearance between the tips of the pin fin and the walls lead to an evenly distributed coolant flow around most of the pin fins. The temperature distributions of the pin fins depend highly on their locations relative to the IGBT modules. The findings from the current study can be useful in future efforts to optimize the thermal performance of IGBT inverters.

Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel

In turbomachinery design, the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial turbine wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase of exhaust gas temperatures in the last years, thermomechanical fatigue in the turbine wheel came more into focus. In order to account for the thermally induced stresses in the turbine wheel as a part of the standard design process, a fast method is required for predicting metal temperatures. In order to develop a suitable method, the mechanisms that cause the thermal stresses have to be understood. Thus, in a first step, a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results, the main heat transfer mechanisms are identified, which are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures. With this understanding, two fast methods to calculate the transient temperatures in a radial turbine were developed. The first method is based on a standard method for transient fluid/solid heat transfer. In this standard method, heat transfer coefficients are derived from steady-state computational fluid dynamics (CFD)/conjugate heat transfer (CHT) calculations and are linearly interpolated over the duration of the transient heating or cooling process. In the new method, this interpolation procedure was modified to achieve an exponential behavior of the heat transfer coefficients over the transient process in order to enable a sufficient accuracy. Additionally, a second method was developed. In this method, the specific heat capacity of the solid state is reduced by a “speed up factor” to shorten the duration of the transient heating or cooling process. With the shortened processes, the computing times can be reduced significantly. After the calculations, the resulting times are transferred into realistic heating or cooling times by multiplying them with the speed up factor. The results of both methods are evaluated against experimental data and against the results of a numerical method known from literature. The methods show a good agreement with those data.