Abstract
Losses in turbine cascade are categorized as profile loss, secondary loss, tip clearance loss and annulus loss. Profile loss occurs due to development of boundary layer on surface of blade [1]. Increase in thickness of boundary layer and adverse pressure gradient increases profile loss. Secondary loss occurs due to turning of flow through flow passage which results in blowing of energy from pressure side to suction side. In turbine rotor blade suction surface leads and tip clearance loss occurs due to leakage of air from pressure side to suction side of the blade through tip clearance. Annulus loss occurs due to development of boundary layer on stationary row of blade. It also occurs in moving row of blade but in moving row of blades boundary layer is scraped by flow over the blades. This paper presents effects of variation of pitch-chord ratio on secondary loss.
Highlights
Secondary losses occur because of unwanted loss of energy due to formation of vortices and turning of flow [2]
Variation of secondary losses with variation of pitch is shown by Figure 8 excluding the pitch chord ratios of 0.42 and 0.44
Value of secondary loss is indicated by value of coefficient of lift and variation of lift and drag force along span which depends upon pitch-wise and span wise pressure gradients
Summary
Secondary losses occur because of unwanted loss of energy due to formation of vortices and turning of flow [2]. When the area of curved passage increases, pressure rises and flow is decelerated. This causes increase in thickness of boundary layer at walls. It is assumed that flow follows the blade passage and some energy is lost in changing direction of flow. The suction surface and pressure surface of blade are not symmetric, so pressure on suction side is different from pressure on pressure side of aerofoil All these contribute to variation of pressure as flow proceeds through passage. Loss of energy occurs due to these vortices, resistance to flow and adverse pressure gradient
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