fluid mechanics - lesson 11 Flashcards
define turbulent flow
when fluid flows in an irregular pattern
= increases surface drag
define laminar flow
A type of fluid flow in which fluid moves smoothly in individual layers or streams
= minimises surface drag
what is Bernoulli’s principle?
as the velocity of a fluid increases, the pressure the fluid exerts on an object decreases
velocity is inversely proportional to pressure
what is the boundary layer?
the thin layer surrounding or attached to the ball
moves with and stays on the object
how does pressure gradient/differential affect form drag?
increased pressure gradient between front and back of the object increases form drag
how does a rough surface affect the boundary layer?
increases thickness of the boundary layer, magnifying affects of boundary layer
what is the separation point?
the position where the oncoming fluid detaches from the boundary layer on the ball
how does an early separation point affect form drag?
earlier separation point, convergence will occur further behind the object, bigger the pocket of turbulent fluid behind the object
therefore, a lower force pushing against back of the object, and greater pressure differential, greater form drag will be
what are the characteristics of the turbulent pocket behind the object?
high velocity, low pressure fluid
how does a smooth surface affect surface drag and form drag?
laminar flow over the surface decreases surface drag
but earlier separation point creates a large turbulent pocket at the back of the ball
greater pressure differential, greater form drag
how does a rough surface affect surface drag and form drag?
turbulent flow over the surface increases surface drag
but later separation point creates a smaller turbulent pocket at the back of the ball
smaller pressure differential, lower form drag
how does a rough surface affect form drag?
causes a late separation point creating a small turbulent pocket causing a smaller pressure differential and less form drag
how does a smooth surface affect form drag?
causes early separation point creating a large turbulent pocket at the rear of the ball causing a large pressure differential and greater form drag
how does the low velocity of the object affect form drag?
causes late separation point creating a small turbulent pocket and therefore a smaller pressure differential between front and back of the ball, decreasing form drag
how does the high velocity of the object affect form drag
causes early separation point creating a large turbulent pocket and therefore a greater pressure differential between front and back of the ball, increasing form drag
