Fundamentals Of Turbomachinery By William W Peng [new] -

“If you throttled the gate too far closed, Leo, you moved left on the curve. Flow dropped, but the specific speed (( N_s = N \sqrtQ / H^3/4 ))—Peng’s master index—stayed constant. Your machine is still geometrically similar to its design, but hydraulically mismatched.”

Spend two weeks just drawing triangles for different scenarios (axial, mixed, radial flow). If you skip this, later chapters will be incomprehensible. Fundamentals Of Turbomachinery By William W Peng