I think that dynamic stall is just a term for accelerated stall. You are saying that they are different stalls.
Yes, I am suggesting that the two are quite different.
Probably better if I waffle on a bit about stalls rather than try and pick out specifics. Some of the following stuff will be familiar, some not so familiar.
There is a variety of “different” sorts of stalls. The terminology can be a bit loose at times and that doesn’t aid understanding.
Regardless of whatever terms you may read in various books, the main types of stalls with which pilots should be familiar are described below.
Stalls occur when the airflow runs up against a pronounced adverse pressure gradient. This just means that, as the airflow goes on its merry way, if the local downstream static air pressure gets less (we refer to a “favourable” pressure gradient), it’s a bit like getting water to run downhill; the airflow accelerates and has a wonderful time. If, however, the local downstream static air pressure increases (an “adverse” pressure gradient) then it’s a bit like trying to get water to run uphill; the airflow doesn’t like it and slows down. If the airflow slows right down, it eventually gets to the point where it goes off and does its own thing and leaves the contours of the structure about which we would like it to move (we say that the flow “separates”). This process, in the extreme, results in significant regions of separated flow, lots of turbulence and we talk about the flow “stalling”. The different types of stalls just reflect different ways we can set up an adverse pressure gradient leading to a stall. The varying characteristics we can see with stalls just reflect the greater or lesser extent to which the gross flow tends to be relatively steady or unsteady during the process.
Certification Stall This is the very nice and sedate stall where the speed reduction to the stall is slow (at a rate originally not more than 1 mph/sec and, subsequently, not more than 1 kt/sec reduction in speed). While the regulatory certification specifics have varied a little over the years, the general idea is that the recovery occurs once there is a positive sign of stall (especially a pitch break, or nose drop) – unstall the wing by reducing the pitch attitude, roll wings level if there was a wing drop and, once positively unstalled (usually speed increasing through 1.2Vs), increase power and recover from the diving attitude.
This type of stall is used to determine the certification (or AFM/POH) stall speed and, subsequently, takeoff and approach speeds. While it is often referred to as a 1g stall, the stall occurs, necessarily as the power is low/idle, during a slightly less than 1g descent. Generally, this sort of stall in a certificated aircraft is fairly well-behaved. As such, it is not of much value for training beyond an initial exposure.
Turning Stall This is usually approached during a steady turn so that there is a load somewhat in excess of 1g. The wing sees this as a heavier aircraft and the stall speed will increase proportional to the square root of the load factor.
Accelerated Stall If the approach to the stall is a little more aggressive than for the 1g stall (the rate of speed reduction is somewhat in excess of 1 kt/sec), either wings level or in a banked turn (you may see the term “wind up turn” in some books), then the stall and post stall manoeuvres might get a little more interesting. We might see significant wing drop, spin entry (especially if the pilot doesn’t prevent slip/skid during the stall manoeuvre) and departure from controlled flight. Especially at low level, this is not a good idea in the normal course of things ...
As the main training concern with stalling is the very dangerous stall during the turn onto final, where we need to minimise height loss and get the aircraft back under control quickly and effectively, we have seen a traditional emphasis on training using an accelerated wings level or turning (or turning/descending) approach to the stall. In this, very dynamic, situation we can see all sorts of aircraft antics during the post stall recovery.
One problem was that folks in the training side of the house tended to lose sight of the main thrust in recovery which was to get the wings unstalled. After some accidents some years ago, the Industry started to lift its game and the emphasis, progressively, is changing to emphasise the need to get unstalled before things get needlessly exciting. As an aside, for routine, normal category operations, a far better plan is to stay away from the stall other than on training occasions when you may have a specific interest in playing with stalls.
Dynamic Stall If the approach to the stall involves quite high accelerations and very high pitch rates, the nature of the stall aerodynamics changes quite considerably. As the wing transits the normal stall angle, the wing sees a short-lived spanwise vortex formed which then sheds rearwards. During this process, the flow reattaches and the lift force can increase quite significantly until the vortex effect ceases.
This phenomenon rarely is seen in fixed wing aircraft (the pitch rates are too low) but is very relevant to rotary wing aerodynamics (retreating blade stall) where it often limits the maximum forward flight speed for a helicopter.
Also it is relevant to flapping wing aerodynamics (insects and birds) and wind turbine power generation. For man-made structures, the dynamic load variations can cause concerns with structural strength and fatigue lives.
Mach Stall (or Shock Stall) When the flow over the aircraft surfaces gets toward the speed of sound, we see the formation of weak shock regions which strengthen as the speed increases. Associated with the shock regions, there are rapid flow discontinuities and it is very easy for the airflow to separate from the aircraft surfaces in a manner similar to that seen during a normal, low speed stall. Separation at higher transonic Mach numbers results in aircraft movements similar to what we see in low speed stalls and we refer to Mach or Shock stalls. Obviously, this is not of much importance to the PPL/CPL level of flying activity but, if you end up playing with fast aircraft, transonic aerodynamics becomes a subject of considerable interest.
A couple of thoughts to add, if I may. There are two specific concerns with shock stalls (these caused much angst in the early days of high speed flight) which have largely been designed out of contention in more modern high speed aircraft.
Due to shock downstream separation, we can see both a significant reduction in control effectiveness due to disrupted airflow over control surfaces (especially the elevators - one of the reasons higher speed aircraft generally have all flying tailplanes or stabilators) and, due to both separation and a transonic aft movement of the CP (in subsonic flight, CP - strictly we refer to the aerodynamic centre but you can think of CP for this discussion - typically is around 25% chord while, for supersonic flight, 50% chord), we can see a quite significant and (for a conventional subsonic design, difficult to control) nose down pitching moment (often referred to as "Mach tuck") and very high control stick loads should the flow over the elevators remain attached.
Both of these effects were responsible for numerous aircraft losses during early days of high speed flight and it took quite some effort for the design and flight test community to sort out just what was going on in the transonic flight region. It was due to these sorts of problems, and the significant drag rise in the region of Mach 1 which led to the coining of the term "sound barrier".
If you have any specific questions, post them and I will endeavour to answer them without too much confusing technobabble.
