I have been reading about the term Blade Loading and Stage loading in case of Axial Turbines and Compressors, however, I would like to know what does the term "loading" here exactly refers to? What I also read was that if we increase the number of blades then the Blade loading for each blade will reduce but the friction and weight will increase, then what is the optimum number of blades one should have?
The term “blade loading” is basically the same as “pressure ratio”. A blade with a higher blade loading causes the exit pressure from that blade stage to be higher than if the blade loading was lower. Hence, the pressure ratio (exit pressure/inlet pressure) is higher when the blade loading is higher.
The optimum number of blades is a very complex problem. But, in simple terms, too many blades, and the weight is too much, too few blades, and either the exit pressure of the compressor is lower (which makes the engine less fuel efficient), or the pressure ratio across each blade is higher, and the engine is much more likely to suffer compressor stalls. The fuel control may have to allow only a very slow acceleration and deceleration rate, to avoid stalls. It may also stall more easily in crosswind situations. Neither of these are ideal in a take-off situation. You don’t want the engine coughing and losing thrust when you are past the point of aborting the take-off, but aren’t high enough to fly a circuit and land.