Conjugate Heat Transfer Calculations Research Articles

Analysis of internal cooling geometry variations in gas turbine blades

The present investigation analyzes the effects of major geometrical modifications to the interior of a convection cooled gas turbine rotor blade. The main focus lies on the flow of the leading edge channels and the impact on the heat transfer. An experimental approach is performed with flow visualization via paint injection into water. Also numerical calculations are carried out in two sets, on the one hand water calculations accompanying the experiments and on the other hand conjugate heat transfer calculations under realistic engine conditions. The latter calculations are still ongoing delivering preliminary results.

On the Temperature Measurement Bias and Time Response of an Aspirated Thermocouple in Fire Environment

To examine the uncertainty of thermocouple temperature measurements, the present study uses numerical simulations and analytical solutions to investigate the heat transfer processes associated with double shield aspirated thermocouple. This study is divided into two parts. First, 3D CFD calculations for real geometries are performed to understand the flow characteristics of double shielded aspirated thermocouples. Based on iso-thermal flow calculations for real geometry, conjugate heat transfer calculations for a 3D simplified geometry are performed to investigate the thermocouple radiative exchange errors that may be important in a fire environment. The results of the 3D heat transfer calculation are compared with algebraic solutions from a previously developed simple energy balance model and the algebraic model shows acceptable results compared to the 3D CFD model, despite its many assumptions and idealizations. A parametric study was conducted to quantify the thermocouple errors for various gas temperature and surrounding conditions. In this manner, the present study improves our understanding of the uncertainty of thermocouple temperature measurements.

Conjugate Heat Transfer Computation for Evaluation of Single-Blow Method for Compact Fin-Tube Heat Exchangers

Computations have been carried out to evaluate heat transfer coefficients given by the single-blow method that is characterized by a transient and conjugate heat transfer problem between the fluid and the solid. Both heat conduction and convection equations are solved numerically to obtain the transient fluid and fin temperature distributions. Finite volume solutions indicate that the fin temperature distribution of the single-blow method varies with time and position and that the fluid temperature distribution of the single-blow method is close to that observed in the steady-state computation specified with the constant wall temperature condition. It is found that the local heat transfer coefficient resulting from the single-blow method is almost identical to that from the steady-state constant wall temperature computation and is nearly time-independent.

Conjugate Heat Transfer Calculation of a Gas Turbine Rotor Blade with Ribbed Internal Cooling Passages

The present paper reports on numerical prediction of temperature distribution of the rotor blade in a gas turbine, which has ribbed serpentine passages for internal cooling. The three-dimensional numerical analysis was conducted by thermal conjugation of inside and outside fields, of the blade, which consists of convection heat transfer around the blade, thermal conduction in the blade material and internal cooling. Correlations of heat and mass transfer in ribbed channels were applied to evaluate heat transfer rate of the internal cooling. The predicted blade temperature profile for the rating condition coincides with the distinctive features of damage on an actual blade. And that profile is in agreement with local temperature estimated by destructive test of the blade. Moreover, the conjugate calculation demonstrates transitional variations in the blade temperature, which are essential for life evaluation of the blade, and clarifies the thermal behaviors of the blade in start-up and shutdown processes.

Study of natural convection in supercritical CO 2 cold wall reactors: Simulations and experiments

Fluid flow patterns and temperature profiles within cold wall, high pressure supercritical fluid (SCF) reactors were investigated by simulation and experiment at conditions relevant to the deposition of copper and other metals for applications in microelectronics. Steep thermal gradients between the heated platen, the bulk fluid, and the reactor walls produce large density gradients in the supercritical fluid. Rayleigh numbers are in excess of 1 × 10 10 and the flow is highly turbulent. Natural convection and buoyancy forces dominate the flow within the reactor in both the batch (closed domain) and continuous flow (open domain) configurations. The situation is unlike that in low pressure chemical vapor deposition reactors in which thermal gradients do not give rise to significant density gradients, flow is laminar, and forced convection dominates natural convection. Temperature distributions and flow patterns within cylindrical cold wall reactors containing supercritical carbon dioxide were simulated by computational fluid dynamics (CFD) and conjugate heat transfer calculations. Good agreement with experiment was achieved. The implications of the results for reactor design are discussed.

4335 RANSによるタービン翼の伝熱解析(S60-1 ガスタービン(1),S60 ガスタービン)

The present paper reports on bench-mark tests of Reynolds averaged Navier-Stokes (RANS) calculations of turbine blade heat transfer. Two sets of the bench-mark problems for the linear eddy-viscosity models with various modifications are solved by three dimensional steady-state calculation. The original models tested are the one-equation model by Spalart and Allmaras, the k-ε model and the k-ω model. One of the bench-mark problems, simulating a previous wind tunnel test, is prediction of local heat transfer coefficient on a stationary blade in a single cascade. Another one is estimation of local blade temperature by conjugate heat transfer calculation simulating an internal-cooling blade in a gas turbine. Computational results present that the k-ω model bounded by turbulence time scale and the shear stress transport (SST) model with the modified k production term reasonably simulate the measurements.

ガスタービン動翼内部リブ付き流路の冷却性能評価(一般セッション 冷却)

This paper reports on numerical assessment of cooling performance of internal ribbed channels in a rotor blade installed in a power generation gas turbine. Roughness functions of heat and mass transfer for fully developed flow in a rectangular cooling channel with two opposite angle-ribbed walls were estimated by using Large-Eddy Simulation (LES). In order to predict temperature profile of the rotor blade, derived correlations of the roughness functions from the LES were applied to the conjugate heat transfer calculation of the blade. As a result, predicted temperature profile on the blade is in agreement with local temperature estimated from material of the spent blade and numerical results presented characteristic variations of the local temperature depending upon mass flow rate of the internal cooling air.

Parametric study of unsteady flow and heat transfer in a pin-fin heat exchanger

A numerical study has been carried out to analyze the unsteady three-dimensional flow and heat transfer in a parallel-plate channel heat exchanger with in-line arrays of periodically mounted rectangular cylinders (pins) at various Reynolds number and geometrical configurations. The three-dimensional unsteady Navier–Stokes and energy equations are solved using higher order temporal and spatial discretizations. The simulations have been carried out for a range of Reynolds number based on cylinder width (180–600) and a Prandtl number of 6.99 (corresponding to water). Conjugate heat transfer calculations have been employed to account for the conduction in the solid cylinder and convection in the fluid. The thermal performance factor (TPF) increases significantly when the flow becomes unsteady. The choice of aspect ratio of the cylinders is judged by their relative increase in friction factor and heat transfer at transitional Reynolds number. The TPF is found to increase with the increase in pitch of the cylinders. The increase in channel height enhances the TPF though the heat transfer decreases at higher channel height.

A conservation-based discretization approach for conjugate heat transfer calculations in hot-gas ducting turbomachinery components

A numerical procedure has been developed for simulation of conjugate heat transfer in generalized coordinates and used in some typical turbomachinery applications. Discretized equations for nodes located exactly on the solid–fluid interface were derived using energy conservation principles, yielding the corresponding temperatures directly, without the need for inter- or extrapolation from adjacent nodes. A finite-volume-based computer code was used along with the SIMPLE algorithm and the k– ϵ turbulence model. The turbulent flow and heat transfer in a stepped labyrinth seal and in an effusion-cooled combustor liner have been studied and results were compared with measured data showing good agreement. In the labyrinth-seal case, the comparisons were in terms of surface temperatures and Nusselt numbers, while for the effusion-cooling case in terms of the streamwise velocity and the film-cooling effectiveness for different blowing and density ratios. In the latter case, two different liner materials were used to study the influence of the thermal conductivity on film-cooling characteristics and the agreement was better for the lowest of the two conductivities. The dominant flow structures could be captured with good accuracy.

DNS of Turbulent Heat Transfer in Channel Flow With Heat Conduction in the Solid Wall

The Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in the two-dimensional turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed at constant friction Reynolds number 150 and Prandtl numbers between 0.71 and 7 considering the fluid temperature as a passive scalar. The obtained statistical quantities like root-mean-square temperature fluctuations and turbulent heat fluxes were verified with existing DNS studies obtained with ideal thermal boundary conditions. Results of the present study were compared to the findings of Polyakov (1974), who made a similar study with linearization of the fluid equations in the viscous sublayer that allowed analytical approach and results of Kasagi et al. (1989), who performed similar calculation with deterministic near-wall turbulence model and numerical approach. The present DNS results pointed to the main weakness of the previous studies, which underestimated the values of the wall temperature fluctuations for the limiting cases of the ideal-isoflux boundary conditions. With the results of the present DNS it can be decided, which behavior has to be expected in a real fluid-solid system and which one of the limiting boundary conditions is valid for calculation, or whether more expensive conjugate heat transfer calculation is required.

Dual reciprocity BEM–BDIM technique for conjugate heat transfer computations

Numerical simulation of conjugate heat transfer problems by methods based on the boundary element method (BEM) promises great flexibility of the computational model. A combination of dual reciprocity BEM for computation of heat conduction in solid regions with boundary domain integral method for computation of heat transfer and fluid flow in fluid regions represents a promising way in numerical simulation of conjugate heat transfer. It combines boundary-only discretisation of solid parts and boundary and internal discretisation of fluid regions. In order to efficiently apply iterative solvers, the subdomain technique is used both in solid and in fluid parts of the computational domain. The results are compared with those of a thermal shock problem achieved by a pure boundary domain integral formulation and is verified on the test case of conjugate natural convection in a cavity with conducting side wall.