Stagnation Pressure,the Bernoulli Equation,and the Steady-Flow Energy Equation

Abstract

The Bernoulli equation is arguably the most commonly used equation in fluid mechanics. For the incompressible, inviscid flow along a streamline, the Bernoulli equation states that the total head of the fluid (the sum of the pressure head, velocity head, and elevation head) is constant. Neglecting elevation changes, the Bernoulli equation therefore limits the maximum pressure coefficient in a flow to 1, which occurs at stagnation points in the flow. Normally, the action of viscosity causes the total head in a fluid to decrease in the streamwise direction, which means the stagnation-point pressure coefficient is less than 1. However, at low to moderate Reynolds numbers, where viscous forces are most significant, stagnation-point pressures exceed 1. This counterintuitive result is explained by reference to the shear work term in the steady-flow energy equation.