Lakhasly

A fluid coupling is shown in Fig.The notations U, V, and Vr continue with their meanings, that is, the blade velocity, absolute velocity of fluid, and the velocity of fluid relative to the blade, respectively. Just as there are different designs of the pumps or the turbines with varying parameters (D1, D2, A1, A2, @1, @2,etc.), there are various designs of fluid coupling and torque converters.But these possibilities do not alter the analysis because the torque interactions depend on the tangential components of the fluid velocities.The velocity triangles can be drawn corresponding to the two elements, in order to determine the interaction of the torques/energy/power.It is quite possible that the outlet of the pump impeller and the inlet of the turbine runner may be in the radial direction [as in Fig.Also, the velocity triangles are as practiced with reference to the respective machines.The additional subscripts p and t signify the pump and the turbine, respectively.Naturally, the velocity triangles become the reference for analysis.9.3(b)].

A fluid coupling is shown in Fig. 9.3(b), where there are only two elements: (a) The pumping element
and (b) the turbine element. The interacting faces of the elements guide the oil flow in the axial direction.
The flow from the pump to the turbine is at a larger radius. The return flow from the turbine to the pump
348 Turbomachines
is at a smaller radius. The velocity triangles can be drawn corresponding to the two elements, in order to
determine the interaction of the torques/energy/power. As the flow is parallel to the axis, the velocity triangles are on a plane that is parallel to the axis. For the case of the fluid coupling, Sr
is equal to 1 and Nr
is
less than 1. The blade velocities of the turbine blades are, therefore, less than those of the pump blades.
It has to be remembered now that the analysis is with respect to the flow of fluid in the two (or three)
elements of the whole device, that is, the pumping unit (the stator unit) and the turbine unit. Naturally, the
velocity triangles become the reference for analysis. Also, the velocity triangles are as practiced with reference to the respective machines. It is quite possible that the outlet of the pump impeller and the inlet of the
turbine runner may be in the radial direction [as in Fig. 9.3(a)], or in the axial direction [as in Fig. 9.3(b)].
But these possibilities do not alter the analysis because the torque interactions depend on the tangential
components of the fluid velocities.
The notations U, V, and Vr continue with their meanings, that is, the blade velocity, absolute velocity of fluid,
and the velocity of fluid relative to the blade, respectively. Subscripts 1 and 2 continue to mean the inlet and
outlet conditions, respectively. The additional subscripts p and t signify the pump and the turbine, respectively.
Just as there are different designs of the pumps or the turbines with varying parameters (D1, D2, A1, A2,
@1, @2,etc.), there are various designs of fluid coupling and torque converters. Apart from that, the power
input at the pumping unit must essentially be higher than the power output at the turbine unit.