# Stagnation pressure and Stagnation Points

by mikeyboy22
Tags: points, pressure, stagnation
 Sci Advisor P: 1,498 Stagnation (or total) pressure is kind of a measure of a fluids energy, as I think of it. According to Bernoulli's, a fluid has three forms of energy, which we are already familiar with. Internal, kinetic and potential. Kinetic and potential we know from statics or kinematics, and internal is something we picked up thermodynamics. Now, the idea of total pressure is that if we can isentropically convert all of the potential and kinetic energy into internal energy, then we have this value. So, a shock is essentially a huge energy killer. If we assume a perfect gas, where cp is a constant, then we can write: $$s_2 - s_1 = c_p \ln\frac{T_2}{T_1} - R \ln\frac{p_2}{p_1}$$ If we consider thsi equation across a shock, then: $$s_{2a} - s_{1a} = c_p \ln\frac{T_{2a}}{T_{1a}} - R\ln\frac{p_{2a}}{p_{1a}}$$ However, $$T_{2a} = T_0 = T_{1a}$$, so: $$s_2 - s_1 = -R \ln\frac{p_{0_1}}{p_{0_2}}$$ or: $$\frac{p_{0_1}}{p_{0_2}} = e^{-(s_2-s_1)/R}$$ Because $$s_2>s_1$$ the total pressure always decreases across a shock wave. Anyways, hope this helped a little with your understanding, if you have any other questions, feel free to ask.