Stagnation Pressure

Figure 3.23 : Stagnation Point on (a) Simple Body and (b) a complicated Body

 

Consider the application of the above form of Bernoulli equation for the flow about a body such as an aeroplane as shown in Fig.3.23. Let rs be a streamline that passes through the stagnation point of the flow, i.e., the point where the flow is brought to rest or where the velocity is zero. Applying the Bernoulli equation along rs we have,

$$p_1~+~{{\rho V_1^2 } \over 2}~=~ p_2~+~{{\rho V_2^2 } \over 2}~=~..=~...~=~ p_s~+~{{\rho V_s^2 } \over 2}~$$ (3.72)

where p_s and V_s are the pressure and velocity at the point s. It is known that V_s= 0. Therefore,

$$p_1~+~{{\rho V_1^2 } \over 2}~=~ p_2~+~{{\rho V_2^2 } \over 2}~=~..=~...~=~ p_s~~$$ (3.73)

p_s is referred to as Stagnation Pressure. Obviously it is the maximum pressure experienced by the fluid. It becomes a very convenient constant for the Bernoulli Equation for aerodynamics flows. It is the pressure experienced by the fluid when it is brought to rest. it is as if the kinetic energy of the flowing fluid is converted into pressure as a consequence of the fluid being brought to rest.

The term "p" is the pressure seen by the moving fluid and is referred to as Static Pressure.

(c) Aerospace, Mechanical & Mechatronic Engg. 2005
University of Sydney