98 Mar B5 May 2016 Page 9 Of 22 Question 7 Turbine Blade Flow Parti Variation In Velocity And Pressure Refer To The Exam 1 (82.34 KiB) Viewed 25 times
98-Mar-B5 May 2016 Page 9 of 22 QUESTION 7 TURBINE BLADE FLOW PARTI VARIATION IN VELOCITY AND PRESSURE Refer to the Examination Paper Attachments Page 16 Pressure and Velocity Variation. Consider conditions at the inlet of a multistage pressure compounded (pressure difference across each stage) impulse steam turbine. Sketch on the attached graph on Page 16 the variation of steam pressure and steam velocity (absolute velocity) as steam passes through the fixed and moving blades of four stages of such a turbine. Return Page 16 with the examination answer booklet. (4 marks) PART IL EFFECT OF BLADE LENGTH Refer to the Examination Paper Attachments Page 15 Steam Turbine Velocity Diagram. In a multistage steam turbine near the exhaust of the turbine the blade length increases substantially necessitating twisted blades where the blade angle changes progressively from the root (base) to the tip (top). (a) Explain why the length of the blade must increase and why this change in shape of the blade is necessary. (b) Assuming that the Steam Turbine Velocity Diagram on Page 15 represents the conditions at the root (base) of the blade: (Sketch the velocity diagram at the root (base) of the blade. (ii) Sketch the velocity diagram at mid-length (half height) of the blade. (iii) Sketch the velocity diagram at the tip (top) of the blade. The diagrams must show clearly how the velocity diagrams change so as to determine the shape of the blade. ( 6 marks) [ 10 marks)
98-Mar-B5 May 2016 Page 16 of 22 NAME QUESTION 7 PRESSURE AND VELOCITY VARIATION STAGE 1 STAGE 2 STAGE 3 STAGE 4 FIXED BLADE MOVING BLADE FIXED BLADE MOVING BLADE FIXED BLADE MOVING BLADE FIXED BLADE MOVING BLADE PRESSURE AND VELOCITY DISTANCE THROUGH TURBINE On the above diagram show the pressure variation through the first four stages of a multistage pressure compounded impulse turbine. Show pressure as a solid line Show velocity as a dashed line (absolute velocity relative to turbine casing)
98-Mar-B5 May 2016 Page 15 of 22 QUESTION 4 & QUESTION 7 PART II STEAM TURBINE VELOCITY DIAGRAM Nomenclature for velocity vectors and angles 0 VS1 VR1 al 0 VB 8 VR2 Vs2 Ve Vst VR1 Absolute steam velocity entering moving blades Relative steam velocity entering moving blades VB Moving blade velocity VRZ Vsz Relative steam velocity leaving moving blades Absolute steam velocity leaving moving blades
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