TURBOMACHINES Chapter 1 INTRODUCTION 1 Definition A turbomachine

TURBOMACHINES Chapter 1 INTRODUCTION 1

Definition: A turbomachine is a device in which energy transfer occurs between a flowing fluid and a rotating element due to dynamic action, and results in a change in pressure and momentum of the fluid. Principal components of a turbomachine: i. A vane carrying a rotating element (rotor, runner, impeller), ii. A stationery element (guide blade or nozzle), iii. An input and/or an output shaft, iv. A housing or casing, 2

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Types of turbomachines: 1. According to energy consideration; a. Turbomachines transferring rotor energy to fluid energy. E. g. pumps and compressors. b. Machines transferring fluid energy to a rotor energy. E. g. turbines (steam, gas and water) 2. According the direction of flow; a. Radial flow as in centrifugal pumps, fans, turbines and compressors. b. Axial flow as in axial flow pumps, compressors, fans and turbines. c. Mixed flow as in Francis turbine. d. Tangential flow as in Pelton wheel. 3. According to the action of the fluid on the moving blades; a. Impulse machines where fluid energy is converted into impulsive force by changing the direction of the fluid as in a steam turbine (De-Laval and Pelton wheel 5

Following points must be considered while selecting repeating variables: a. As far as possible independent variable should be selected. b. The selection should be in such a way that one variable contains the geometric property, second variable contains the flow property and the third variable contains the fluid property. 6

Variables with geometric property are: i. Length (L): blade chord or blade length ii. Diameter (d): rotor diameter iii. Thickness (t): blade thickness iv. Height (h): blade height Variables with flow property: i. Velocity (u): blade velocity ii. Velocity (V): flow velocity iii. Speed (N): rotation speed iv. Volume flow rate (Q) v. Mass flow rate (m) vi. Acceleration (a) vii. Angular velocity (ω) 7

Variables with fluid property: i. Gas density (ρ) ii. Bulk modulus (K) iii. Force (F) iv. Dynamic viscosity (μ) v. Pressure difference (Δp) vi. Power (P) vii. Elasticity (e) viii. Surface tension (σ) ix. Specific weight (w) x. Stress xi. Resistance (Ω) 8

Model to prototype similarity conditions: • Geometrical similarity: model and prototype are said to be similar if the ratios of all corresponding linear dimensions of the system are equal. for geometric similarity: • Kinematic similarity: two systems are said to be kinematically similar if they are geometrically similar and the ratios of velocity at all homologous points are equal. for kinematic similarity: • Dynamic similarity: dynamic similarity is said to exist between model and prototype, if they are geometrically and kinematically similar, the ratios of the corresponding forces acting at the corresponding points are equal. for dynamic similarity: 9

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