Turbine Cascade Laboratory1. ObjectiveThe turbine cascade laboratory is designed for the turbine compressor performance to be measured and then used to therefore optimise the blade shape and pitch to chord ratio. The deviation, deflection, and stagnation pressure loss as a function of distance and angle of incidence are the parameters of interest and need to be calculated. These are calculated by the following equationsIncidence angle (I) = 1 - 1Deviation () = 1 - 1Mean Deflection () = 1 + 2The air inlet angle can be varied by placing the cascade at an angle by a set of angled boxes.

Figure 12. IntroductionA cascade is used to measure the performance of the blades. The full circle of blades cannot be measured so part of it is used, as it is smaller (therefore easier to measure performance) and cheaper. The cascade represents the compressor blades in a gas turbine engine which are fixed blades (stators).The use of a cascade allows the observation of the affect that the blades have upon each other. The use of a wind tunnel gives an approximation of the effects of two dimensional flow over the blades allowing changes to be made for optimisation of performance. 3. Experimental apparatus and procedureAppartus Tunnel (consisting off contraction, diffuser and fan) Manometers Pitot tubes Claw Probe Cascade Angled Boxes 0o, 35o, 60oProcedureInitial checkWith the fan turned off, set the balance manometer to the reference position, zero the manometers and record the zero errors.With the 0o box attached without the cascade, do the following checks when the fan is switch on with its minimum speed.1. Set the traversing table to 0 angle, with the probe in the approximate centre of the tunnel outlet and the rotate the claw probe until the balance manometer is back at the reference mark. The flow is parallel to the tunnel axis within +/- 0.5o and the angle reading should be 0. Note the error, which should be allowed for in all subsequent readings.2. Compare the reading from the central claw probe tube with static reading before the contraction to establish an error in the assumption of constant stagnation pressure in the contraction.Measurements1. Mount the appropriate angled box and cascade onto the wind tunnel, and set the traversing table angle to match the box angle. The horizontal traverse should now be parallel to the cascade face.2. The claw probe should match the blade exit angle and set the nose one chord width downstream from the cascade. The vertical and horizontal positions should be at the central point of the outlet air stream.3. With the fan switched on, adjust the angle of the claw probe to restore the balance manometer to its reference mark and record the readings.4. In steps of 0.1 up to 2 inches, traverse the probe horizontally, recording the claw probe angle position when the manometers are balanced and the central tube manometer reading.5. Continue the traverse over three blades???6. Switch the fan off and repeat the procedure with the different angle box.7. Repeat the above over a number of varying inlet conditions???The readings taken during the experiment were from pitot 1, 3 and 5 as well as the angle of the claw probe.Pitot 1 measured the stagnation pressure after the cascade with the claw probe. Pitot 3 measured the static pressure before the cascade with the pitot parallel to the direction of the flow. Pitot 5 measured the static pressure before the contraction in the wind tunnel with the pitot parallel to the direction of the flow.

4. Results PresentationDeviation and Deflection

Figure 2

Figure 3Figure 1and Figure 2 show the deviation and deflection for the 0o cascade.

Figure 4

Figure 5Figure 3 and Figure 4 show the deviation and deflection for the 35o cascade.

Figure 6

Figure 7Figure 5 and Figure 6 show the deviation and deflection for the 60o cascade.The graphs above are derived from the raw data in Table 2. With an adjustment using the calibration angle of 3.2o, the following equations are using for the deviation and deflection.Deviation () = 1 - 1Mean Deflection () = 1 + 2Stagnation Pressure loss

Figure 8

Figure 9

Figure 10The stagnation pressure loss shows energy lost in the fluid across the cascade as shown by the non- dimensional equation below.

Using Bernoullis equation as shown below, the term is assumed to be relatively small and therefore the dynamic pressure term is ignored.

Looking at the stagnation pressure loss gives the equation below.

This gives the equation below.

The bottom can be rearranged again to give

Incidence (degrees)-152045

Mean Stagnation Pressure Loss ( mean)0.730.840.90

Mean Deflection ( mean)47.9881.57114.63

Table 1The mean stagnation pressure loss can be found by integrating the reading taken as shown by the equation below where N is the number of readings and L is the maximum length.

Figure 11

Figure 12

5. DiscussionThe peaks in the graph show the trailing edge deviation peaks. However in the deflection graphs they are shown as troughs. This is because As shown by the figures above, the pressure loss increases as the incidence angle (1) increases. This is due to the flow around the blades breaking down due to a separation of flow from the suction side of the blades. This would lead to turbulent boundary layer would also affect the neighbouring blades. As the blades are fixed and not rotating this may not be too much concern for the stator blades.After this is the rotor blades. If the pressure drop is far too high then there will not be enough pressure to turn the rotor and hence the stall.ue to this relatively higher ratio of expansion of steam in the nozzle the steam leaves the nozzle with a very high velocityThe steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.The steam flow is partially reversed by the moving blades, producing a reaction on the blades. Since the pressure drop is small across each row of nozzles (blades),rotating and fixed stators alternate and steam pressure drops by a fraction of the total across each pair, the stators grow larger as pressure drops.The pressure loss peaks in the graphs occur slightly just before the peaks in the deviation vs distance graphs. This means that the peaks occur just before the trailing edge of the blade. In a turbine, there would be no expected net loss in velocity, but a drop in pressure and temperature. This would be reflected in the work done trying to turn the rotor.Too high of an incidence would cause turbulent boundary layer on the du6. ConclusionRepeats - reduce errors to make experiments betterThe claw probe could have been moved in finer increments to give a more accurate set of results with repeats to remove any anomalies.Experimental ErrorsThe experiment consisted of many errors. They were the following: The micromanometer has an analogue reading with a needle fluctuating around the 0 point. This would have human error. The claw probe has an accuracy of 0.05 inch and again consisted of human error (parallax error) as the adjustments were not always at eye level. The protractor accuracy has an accuracy of 0.1o. This could again consist of human error and the fact that as the turbine was running, the vibrations would move the protractor slightly if not held. The readings were taken by different people giving a lack of consistency. In the turbine, there were leaking of air around the bolted parts between the contraction and diffuser and also the diffuser and fan.

7. References[1] Turan, Ideal Cycle Analysis notes. 2012[2] Cohen, H., Rogers, GFC., and Saravanamuttoo, HIH., Gas Turbine Theory. 4th edition 2005, Essex: Longman Group LTD. p. 199-205.[3] Hall, J., Noca, M., and Bailey, R., Cost-Benefit Analysis of the Aerocapture Mission Set, AIAA Paper, 2003-4658, July 2003.Curtis, H.D.,

8. AppendiciesAppendix ADistance Angle alpha 2 (Degrees)

metres03560

054.048.255.8

0.0025447.044.952.6

0.0050850.448.047.7

0.0076251.650.057.6

0.0101651.653.070.6

0.012754.750.364.0

0.0152452.044.358.3

0.0177847.547.653.5

0.0203249.448.950.2

0.0228650.849.550.2

0.025449.354.271.7

0.0279457.054.368.3

0.0304851.349.662.1

0.0330251.245.557.1

0.0355649.850.251.9

0.038151.250.049.3

0.0406451.557.049.3

0.0431851.953.667.2

0.0457254.150.764.7

0.0482651.145.658.6

0.050847.349.853.7

Table 2: Table showing raw data recorded

Appendix BBox Angle03560

Number315315315

Distance Inlet - statOutlet - stagContraction - statInlet - statOutlet - stagContraction - statInlet - statOutlet - stagContraction - stat

metresmmWgmmWgmmWgmmWgmmWgmmWgmmWgmmWgmmWg

01.002.589.202.002.508.151.101.709.25

0.002541.003.819.102.053.158.751.051.809.15

0.005081.003.159.102.053.208.801.031.959.20

0.007621.003.309.102.003.208.301.032.759.15

0.010161.003.309.102.053.158.801.031.909.15

0.01271.003.209.102.053.208.801.001.759.03

0.015241.003.009.102.052.408.801.001.659.00

0.017780.983.009.002.003.208.851.001.659.08

0.020320.983.209.002.053.258.901.001.859.15

0.022861.003.209.002.053.258.951.001.959.10

0.02541.003.309.002.053.208.901.001.908.95

0.027941.003.309.102.103.258.901.001.559.10

0.030480.983.009.002.002.308.900.951.509.05

0.033020.902.709.002.003.158.900.951.409.05

0.035560.903.009.002.053.258.950.951.509.05

0.03810.903.209.002.003.308.900.951.809.05

0.040640.903.209.002.003.208.950.902.159.00

0.043180.903.209.002.003.258.950.952.009.00

0.045720.903.109.001.953.208.950.901.558.85

0.048260.902.509.002.003.108.950.901.459.00

0.05080.903.009.002.103.209.000.901.559.00

Table 3: Table showing pressure readings at pitot 1, 3 and 5