Numerical Investigation of Some Heat Transfer Topics with Relevance to Gas Turbines

University dissertation from Division of Heat Transfer, Lund Institute of Technology

Abstract: The first part of the investigation is related to the heat transfer and fluid flow problem inside ribbed ducts with a square cross section. The typical applications of this problem are in the cooling of gas turbine blades and guiding vanes. The second part is related to application of intercoolers in gas turbine systems. The intercooling is performed via intercoolers that usually are water-air heat exchangers. The ducts considered have rib turbulators in order to enhance the heat transfer rate. Firstly, a literature investigation is carried out and examples of different prediction methods for ribbed ducts are presented. Application of these ribbed ducts in cooling for gas turbine blades are discussed. The importance and role of intercoolers in gas turbine systems are discussed and their importance in future gas turbine systems is mentioned. Importance of various heat exchangers and extended surface types is presented and examples of heat exchangers concepts for intercooler applications are considered. A numerical calculation procedure is presented. The governing equations are the continuity, the Navier-Stokes and the energy equations in their general form for incompressible flows. In turbulent cases the time averaged form of this set of equations has been used. The turbulence modeling consists of two low-Re number turbulence models and two methods for determination of the turbulent Reynolds stresses, namely, Eddy Viscosity Model (EVM) and Explicit Algebraic Stress Model (EASM). The model development is carried out to ensure that the original EASM is consistent with the low-Re number k-epsilon turbulence model applied. A certain method is developed to deal with the de-coupling of the velocity and Reynolds stress fields in the collocated grid arrangement that is chosen in this work. The pressure-velocity coupling is handled by the SIMPLEC algorithm in turbulent cases and the PISO algorithm in unsteady laminar flow cases. Seven papers are included. In the first paper turbulent flow and heat transfer in a rotating smooth duct and a ribbed duct is considered. An EVM method with a low-Re number model is applied. The second paper consists of application of EASM and EVM with a low-Re number model to a ribbed duct case and presentation of detailed local variables and flow phenomena. The third paper presents a discussion of the role of intercoolers in gas turbine systems and means to improve performance are mentioned. The fourth paper presents a set of numerical analyses and CFD calculations carried out on various concepts of intercoolers. The fifth paper presents a discussion and comparison of some heat exchanger types readily applicable for a gas turbine intercooler. A comparison of the intercooler core volume, weight and pressure drop is presented. In the sixth paper two low-Re number turbulence models and EVM and EASM models are used to investigate a ribbed duct case. The local results as well as the averaged total values are compared with available experimental results. In the final paper, unsteady calculations for an offset strip fin have been carried out. The mechanisms of heat transfer enhancement are discussed and the creation of the temperature and velocity fluctuations has been investigated and the dissimilarity between them has been proved.

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