The internal cooling passage of a gas turbine blade can be modeled as a ribbed channel. So far, most studies have considered square ribs. However, the ribs can be rounded due to improper manufacturing or wear during the operation. Round ribs have also been tested expecting that they may enhance the thermal and aerodynamic performance. Hence, we have studied two different rib geometries in this study, i.e. square and semicircle ribs. Large eddy simulations (LES) of turbulent flow in a ribbed channel with a dynamic subgrid-scale model are performed. In our simulation, the no-slip and no-jump conditions on the rib surface are satisfied in Cartesian coordinates using an immersed boundary method. We have also conducted an experimental study to validate the simulation. The velocity and temperature fields are measured using hot wire and thermocouple, respectively. The surface heat transfer is measured using the thermochromic liquid crystal with a high spatial resolution. LES predicts the detailed flow and thermal features such as the turbulence intensity around the ribs and the local heat transfer distribution between the ribs, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms responsible for the local heat transfer distributions between the ribs; i.e. the entrainment of the cold fluid by the vortical motions and the impingement of the entrained cold fluid on the ribs. We also discuss the local heat transfer variation of the ribs in connection with flow separation and turbulent kinetic energy. The total drag and heat transfer are calculated and compared between the square and semicircle ribs, showing that two ribs produce nearly the same heat transfer, but the semicircle one yields lower drag than the square one.

In this article, an inverse method for retrieving time-and space-varying heat flux on the surface of a three-dimensional slab with temperature-dependent thermophysical properties from temperature scanning on the opposite surface is investigated. The sequential gradient method, which implements the gradient method in a sequential manner, is employed to solve the nonlinear inverse heat conduction problem. To stabilize the solution algorithm, a cubicspline function is specified in space and a constant or linear function is specified in time without the use of the regularization term. The proposed method is verified with presented computational results for several cases.

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The anisotropic phonon conductions with varying Joule heating rate of the silicon film in Silicon-onInsulator devices are examined using the electron-phonon interaction model. It is found that the phonon heat transfer rate at each boundary of Si-layer has a strong dependence on the heating power rate. And the phonon flow decreases when the temperature gradient has a sharp change within extremely short length scales such as phonon mean free path. Thus the heat generated in the hot spot region is removed primarily by heat conduction through Si-layer at the higher Joule heating level and the phonon nonlocality is mainly attributed to lower group velocity phonons as remarkably dissimilar to the case of electrons in laser heated plasmas. To validate these observations the modified phonon nonlocal model considering complete phonon dispersion relations is introduced as a correct form of the conventional theory. We also reveal that the relation between the phonon heat deposition time from the hot spot region and the relaxation time in Si-layer can be used to estimate the intrinsic thermal resistance in the parallel heat flow direction as Joule heating level varies.