Toofuzzy, the low starting torque is partly compensated by the washers that hold the Discs Pack together via the impact principle by which airfoil shaped blades of a turbine wheel get their good starting torque. In cases where the turbine can start unloaded and "clutched" to a load this is not a problem but if it is directly coupled to s generator the start-up time is much longer but at the target speed a Disc Pack is theoretically more efficient. In practice however the typical Tesla Turbines build by amateurs have not realised the high efficiency that was promised . . .various design deficiencies are the cause of that, resulting in more turbulence than hoped for as well in un-optimised units.
I can see where it would have low starting torque. I wonder if a grooved (vortexed) surface would help.
This, with superficial look at things appears a reasonable option to consider. but it is not. The Tesla turbine derives its torque form laminar flow surface drag. . .not turbulent friction such as occurs in almost all flow devices and turbulence is present all turbines. The Tesla Torque results from the presumed laminar tangential flow over the disc surface while the fluid spirals in a restrained vortex motion to the disc's central outlet. So, a fluid element is forced to flow in a spiral form by the presence of the fluid surrounding it as the initially tangential injection flow must change to partially a radial inward flow.
Should one create spiral channels, even in the exact general average spiral path that the fluid will move between unproved plates, you still totally destroy the tangential flow component that is present between the smooth discs! This way you will in effect have created an impact flow turbine by which torque is created by the rate of change of momentum of the flow in a curved duct. . . this is the type of process that happens in the Heron Turbine and in fact also in conventional webbed radial flow turbines like used in Turbo Charges.. .It would not be Tesla Type Turbine.
In addition that fundamental difference there is much more against that idea. If you have grooved discs then as the turbine would have to operate at a specific constant speed AND at a constant flow AND at constant torque. . .if load variations would occur then the fluid flow has to change and the spiral grooves will have the wrong shape and be useless as torque generators. The flow will want spill over the groove boundaries and this will defeat the grove concept. . .the nature of the groove design would have the specific purpose of containing the fluid in the groove. . .if that does not happen it destroys the curved channel flow and at the same time if the channels ribs are very narrow the fluid can not create surface drag torque at all at other speeds.
So a Tesla Turbine must have smooth discs. All sorts of Disc Types Turbines with vanes on them have been suggested and Patented but they are not Tesla Turbines.
The modification Vortex had created for the Vortex Combined Disc Turbine(VCDT) still retains the smooth discc Tesla Concept. . .That is a critical feature to hold on to.
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