can someone please help me understand why the pressure is like that over the top and bottom surface of this aerofoil please?
Also, what do the arrows point out mean? Why are the front and end ones pointing in?
There are a few interesting aspects to these seemingly innocuous pressure diagrams that bear closer examination.
Firstly, this is a non symmetrical airfoil with a bit of camber. This is why even the first diagram, at 0 degrees, it is generating more upward that downward force. The difference is more apparent at 6 degrees Angle of Attack.
cambered wings can have zero lift at a negative angle of attack
The second item of note is the pressure gradients at the trailing edge. Interestingly, these might be a result of insufficient airspeed, growing worse with increasing AoA.
Part of what makes wings work is the momentum, mv, of the airflow around the wing. As speed increases, in the exact same manner turbulent flow separates from the transom of a boat, the airflow from the top and bottom of the wing is carried past the trailing edge before merging.
This is what would expect to see with a properly functioning airfoil. The calm lower pressure stagnation zone directly behind the wing would not be creating any buffeting on the trailing edge.
The arrows represent the direction the pressures are acting. Pointing towards the wing are increased pressures, and those pointing away are where the wing experiences a decreased pressure. At the leading edge, you can conceptualize this as the point where the air collides with the wing and must be deflected away. Meanwhile, due to fluid dynamics principles (e.g. Bernoulli's principle) the high-velocity air moving around the curved surface is related to a decrease in pressure at those locations. In the diagrams, the leading and trailing edges are being pushed inward while the upper and lower surfaces are being pulled outward. Summing up all the inward (increased) and outward (decreased) pressures, and looking at only the vertical component will result in a single upward force felt by the airplane.