Why is tangential velocity a loss of kinetic energy in a turbine section?

While researching turbine engines I came across a statement

The mass of airflow naturally does not change in the transfer of energy to the rotor system, but the velocity of mass flow being slowed axially is said to account for the energy of flow as the energy of shaft power is increased. In other words, tangential velocity is essentially a loss of kinetic energy to the engine.

Why and how does this the loss occur, and how can this loss be reduced?

I'm not trying to get an in-depth mathematical aspect on that topic as I'm still a beginner with the study of gas turbines, a simpler theoretical non-math explanation would very much be appreciated, thanks!

• I am not sure to understand what you mean by Why is the loss a case. Sep 3 '20 at 13:44
• @BambOo I have made the changes in question Sep 3 '20 at 15:56
• Where did you see the axial velocity is slowed through the turbine ? In fact, density of air is reduced during gas expansion which leads to axially accelerate the flow in order to keep mass flow constant. Cross section surface is gradually enlarged in order to confine air speed. Sep 5 '20 at 18:16
• @Salmonbeing00, I read your post a second time and realised that your question is about engine in general and not only the turbine part. My first answer involve turbine module only. Sep 5 '20 at 18:29