A gas flows along the x axis with a speed of V = 5x m/s and a pressure of p = 10x2 N/m2 , where x is in meters.

(a) Determine the time rate of change of pressure at the fixed location x = 1 (i.e., for the particle currently at x=1).

(b) Determine the time rate of change of pressure for a fluid particle flowing past x = 1. (you are fixed at x=1)

(c) Explain without using any equations why the answers to parts (a) and (b) are different.

Respuesta :

Explanation:

Given that,

Speed = 5x m/s

Pressure = 10x² N/m²

(a). We need to calculate the time rate of change of pressure at the fixed location x = 1

Using formula of rate of change of pressure at fixed location

[tex]\dfrac{\delta P}{\delta t}=\dfrac{\delta}{\delta t}(10x^2)[/tex]

[tex]\dfrac{\delta P}{\delta t}=0[/tex]

(b). We need to calculate the the time rate of change of pressure for a fluid particle flowing past x = 1

Using formula of rate of change of pressure at the given instant

[tex]\dfrac{DP}{Dt}=\dfrac{\delta P}{\delta t}+u\dfrac{\delta P}{\delta x}+\dfrac{\delta P}{delta y}+\dfrac{\delta P}{\delta z}[/tex]

[tex]\dfrac{DP}{Dt}=u\dfrac{\delta P}{\delta x}[/tex]

Put the value into the formula

[tex]\dfrac{DP}{Dt}=5x\dfrac{\delta}{\delta x}(10x^2)[/tex]

[tex]\dfrac{DP}{Dt}=5x\times20x[/tex]

At x = 1,

[tex]\dfrac{DP}{Dt}=100\ N/m^2 s[/tex]

(c). The velocity is instantaneous at x = 1  for a part and for b part the velocity is steady flow.

Therefore, the answer is different for a and b part.

Hence, This is the required solution.