SeveralBoundary condition types ofStructured grid structured grids, usedGrid generation in CFD calculations, including theCartesian Cartesian, cylindricalCylindrical, andBody-fitted body-fitted grids, are described. Physical spacesPhysical space where grids are generated are linked with theComputational space computational spaces. The importance of using fine gridsFine grid for resolving flows near the boundaries is emphasised. It is pointed out that the size of the grid cellsGrid cells can increase when resolving flows away from the boundaries, but the transition from fine to coarse gridsCoarse grid should be gradual. The most important boundary conditionsBoundary condition used in CFD calculations, includingWall wall, inletInlet, outletOutlet, symmetrySymmetry, andCyclic cyclic, are described. Two types of boundaries that can be imposed on the wallsWall are described. These are the fixed value of the variable (e.g. temperature) at the wallWall (DirichletDirichlet boundary condition) and the fixed value of the flux of the variable (e.g. heat flux)Heat flux at the wallNeumann (Neumann boundary condition). TheBoundary condition condition in which there is no temperature jumpTemperature jump at the wallsWall is used unless rarefied gasesRarefied gases under investigation. For transient problemsTransient problem, the boundary conditionsBoundary condition should be supplemented by theInitial condition initial conditions.