Teori strömmek 2

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• Explain what a normal shock is. What happens with the velocity, pressure and total temperature over a normal shock? How is the critical area, A∗ effected? A normal shock is a shock which is perpendicular to the flow (with its normal in line with flow direction). Velocity decreases, pressure decreases, and total temperature doesn’t change (since there is no work done to/by the system) over a (normal) shock. The critical area (sonic throat area) increases
• What is a critical property (such as for example the critical temperature T∗)? Critical properties are the conditions when the flow is sonic (Ma = 1.0). So T* is the temperature when the flow velocity is Ma=1.0
• Which of the properties ho, To, ao, po, and ρo are constants in a flow if the flow is adiabatic and isentropic, respectively? All stagnation properties are constant in isentropic flow h0, T0, a0 are constant in adiabatic flow, but 0, p0 might not be since they will vary throughout the adiabatic flow as the entropy changes due to friction and shocks
• Explain displacement thickness The displacement thickness can be thought of as an index proportional to the “missing mass flow” due to the presence of the Boundary layer. It’s the normal distance to a reference plane representing the lower edge of a hypothetical inviscid fluid of uniform velocity that has the same flow rate as occurs in the real fluid with the boundary layer
• Explain momentum thickness The momentum thickness in an index that is proportional to the decrement in momentum flow due to the presence of the Boundary layer. It’s the normal distance to a reference plane representing the lower edge of a hypothetical inviscid fluid of uniform velocity that has the same momentum flow rate as occurs in the real fluid with the boundary layer.
• What assumption is made to be able to derive the boundary layer equations? 2d-flow, incompressible flow and steady state
• Turbulent flow is dissipative. What does that mean? Kinetic energy gets converted into heat due to viscous shear stresses.
• explain B and beta in reynolds transport theorem B is an extensive property of a fluid (E.g energy, momentum and enthalpy.) is the corresponding intensive value (the amount of B per unit mass). We can therefore get the total amount of B in the control volume by using the integral
• How can we make use of Pascal’s law when analysing manometer tubes? Two points at the same elevation in continuous mass of the same static fluid will be at the same pressure. This is handy in manometer tubes, since we can just know the densities of the fluids in the manometer and the different heights of the interfaces between the different fluids.
• what is a streamline A line that is tangent to the velocity vector everywhere at an instant time. A streamline therefore shows the direction in which the fluid will travel at any point in time.
• What is a pathline The trajectory that the individual particle follows.
• What is a streakline A line created by particles in a flow that have previously passed through a common point.
• The continuum concept is very central in fluid mechanics - explain this concept. Fluid as a continuum means, we consider fluid as continuous medium despite the fact that at molecular level it is not continuous and at macroscopic level it may cluster. We use this assumption so that we can make use of well known differential calculus to solve the physical problems.

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