Tht; turbine performance can be improved simply by minimising the losses. This can be achieved through a number of ways, discussed in the following paragraphs.
Further filtering of the water - such as making the grid at the entrance to the inlet pipe of a slightly finer mesh. Although this will tend to begin to limit the flow when the amount of debris builds up on the grid, it is much easier to keep clean when compared to having to repair damages to the turbine itself, even if the comparison is purely on an accessibility level and ignoring the effort of repairing damages to the turbine itself.
Laminar flow characteristics could be beneficial, not only to the operation of (he turbine itself, but also to the reduction of the losses due to friction. A filter grid is needed to improve the laminarization of the flow entering the nozzle, at the expense of a smaJl pressure drop, but would not be able to ca.use the flow to be entirely laminar due additionaJly to the velocity of the flow causing high Reynolds numbers and falling into the region of turbulent flow.
An unexpectedly high amount of heating of the thrust bearing occurred during the operation of the turbine. Due to the damage that can be caused in this instance, where the heating causes the grease to carbonize and no longer provide sufficient lubrication, it is necessary to provide cooling. This can quite easily be provided by including a water jacket around the thrust bearing, supplied in a manner similar to that of the cooling water for the stuffing box. A pipe tapped from the high~pressure side of the flow, directed through the water jacket and returned to the low-pressure side.
Balancing of the turbine rotor may further eliminate vibration within the system.
Vibration noise tends to initiate premature turbulence, if the flow Reynolds number is near the laminar to turbulent transition. Thus balancing of the turbine, may not only help reduce the amount of mechanical work lost, but also the amount of friction losses, when comparing turbulent and laminar friction losses.
Optimising the design of the draft tube, as discussed in Chapter 2.4.11 and following, would further increase the efficiency of the turbine, since the power is proportionaJ to the head. Optimisation of the draft tube design is covered in the aforementioned chapter.
Being able to restrict the flow within the draft LUbe during partial gate valve opening to ensure that the turbine remain "flooded" during the full range of its potential operating conditions, would increase the efficiency. When the turbine is not flooded, the presence of an air gap implies that not all the blades are producing work at any given point in time.
The turbine should also be disassembled periodically to check for debris restricting the flow, to check the stuffing box packing and the bearings should be replaced as recommended in the bearing design chapter.
Eliminating the leak found in the draft tube pipeline would change the power output, since it would raise the level of the vacuum caused by the exhaust water although such a high vacuum may cause cavitation due to localised low pressure gradients which will result in a decrease in efficiency.
The location of the high-pressure feeder pipe should be in such a position that it is capable of supplying the stuffing box with water even when the level of the water is not at its peak. for example when the turbine is run at lower volumetric flow rates.
Likewise for the pressure gauges, but this applies more to the flooding of the gauge itself, where it is necessary to bleed the air from the gauge. Although it should also be borne in mind that there is much debris and sand that flows with the water in spite of the gate upstream of the pipe inlet which filters larger debris. Should any of this enter the pressure gauge, it is bound to cause failure. Tt is therefore recommended that the gauges be placed halfway up the side of the pipe.
The final results of Figure 5.4.11 show an overlay of the valve, turbine and draft tube efficiencies. It is believed that a higher overall efficiency may be attained if the leak in the draft tube as well as the draft tube itself were modified to suit the ideal case as discussed in previous sections.
Finally, the governing of the turbine is the method of smoothing the power output such that the rpm may be set at 50Hz with minimal variations in power. This is necessary in terms of the power driven components supplied by the turbine. For this particular turbine, with its characteristically high torque at fairly low rpm, gearing to achieve the required 50Hz should prove to be a very productive task. However, as mentioned in the introduction, it was not required that this topic be researched.