The correct answer is:
(d) Exhaust pipes
Explanation: In Computational Fluid Dynamics (CFD), an internal analysis refers to the analysis of fluid flow within a confined region, such as within pipes, ducts, or combustion chambers. These types of flows are generally governed by the interactions between the fluid and the boundaries (walls) of the system.
Combustion (a), Turbulence (b), and Flow over compressor (c) are typically associated with internal fluid flow analyses, where the flow is confined and governed by the geometry and boundary conditions within the system.
Exhaust pipes (d), on the other hand, are generally related to external flow analysis when considering the flow of exhaust gases through an open environment after being discharged. While exhaust pipes might involve some internal analysis of the pipe itself, the exhaust process often pertains more to how the gases exit into the atmosphere, which is an external flow problem.
Thus, exhaust pipes are not typically considered an internal analysis in CFD.