Current Inlet Pressure Distortion Practice

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Experimental Setup

It has been shown by Jumel and DiPietro that the splitting airfoil concept had promise for a transient distortion generator. However, more investigation needed to be done on the splitting airfoil concept. To accomplish this, a splitting airfoil design has been built that is capable of being set at different angles. This enabled tests to be run with different wedge angles while still using the same model. The tests were similar to Jumel’s, being that the steady state total pressure loss was measured at several downstream planes. After viewing Jumel’s results, it was decided that the current focus should be on the first foot downstream. It was not known in this region how the wake would form and interact with the free stream as it moved further downstream. In addition, it was necessary to examine the entire width of the test section to get the complete total pressure patterns. Also, combinations of more than one splitting airfoil in close proximity were investigated. Combinations of airfoils were examined to see how the wakes would interact with each other. This chapter will discuss the splitting airfoil concept that was tested. It will also discuss the setup of the test section and will detail all of the tests that were completed.

Model Development

It was necessary to create a splitting airfoil that would be capable of being set to different angles between 0° and 180°. This device would have some sort of hinge to enable the airfoil to open and close. Therefore, the best alternative was to use an existing hinge to act as the airfoil. This would only approximate the actual device that would be used in front of an engine, but would give test data to see what sort of pressure patterns were capable of being created. The size of the hinge was chosen to be similar to the wedge that Jumel studied so the results could easily be compared to each other. The size of Jumel’s wedge was 1.5 inches along each edge and 1.5 inches wide. This would correspond to an area that was 3 inches tall by 1.5 inches wide if fully opened. The current investigation also focused on different configurations of airfoils that were tested in the wind tunnel. The size of the airfoils used was decreased slightly compared to Jumel’s so that the entire wake of the combination could be measured when testing more than one prototype.
The size of the hinge that was decided on was a hinge that was approximately 2 inches tall and 1 inch wide when fully opened. This size was chosen to match Jumel’s Reynolds number as close as possible while still allowing combinations of more than one hinge to be examined. The pin for the hinge would also have to be removable to allow the hinge to be placed on a strut in the test section. The best sort of hinge would be one that gave the least amount of distortion when in the fully closed position.
A search was done of various hinge manufacturers to try and come up with a suitable hinge. A collection of hinges was found at the McMaster-Carr Website [12]. The one that was chosen was a stainless steel hinge, model 1624A51. The dimensions of this hinge were 2 by 2 inches and the thickness of the metal was 0.060 inches. The hinge also had a removable pin. This hinge was the closest one that met all of the requirements. When fully closed this hinge would have a height of 0.25″ and 2″ when fully opened. This would enable as little distortion as possible when fully closed. A similar design could be used in the actual direct connect testing, although the splitting airfoil would be fitted with an actuation device. The hinge side view when fully closed and opened can be seen in Figure 3.1.
This hinge needed to be cut down to get to the desired size of approximately 2 inches by 1 inch. Hinges are manufactured to have a curved circular metal section that attaches the two different sides to the pin. One half of this particular hinge had 2 curved sections while the opposite half had 3 curved sections. Therefore, in order to make the hinge symmetrical, it was cut so there would be three of the curved sections in the final design. After being cut, the size of the hinge was 2 inches tall and 1.125 inches wide. Set screws were installed in the back of the hinge. These screws allowed the hinge to be set to the angle that was needed for the different tests. The screws would be tightened against the supporting rod that went through the hinge. A drawing of the original hinge compared to the cut hinge can be seen in Figure 3.2. In addition, the actual splitting airfoil used in the tests can be seen in Figure 3.3. Here you can see the set screws that are in the back of the hinge.

Wind Tunnel and Test Section

This section will describe the wind tunnel and test setup that were used in the experiments. More details, including drawings and pictures of the test setup can be found in Appendix A.
All information given below about the wind tunnel came from Jumel’s report previously mentioned [11]. The wind tunnel used was originally designed and built by Tkacik [15] for his experiments on stalled flow. It uses a centrifugal blower built by the Aerovent Corp. (model BIA, size 630, class II). The fan is equipped with a 15 horsepower electric motor. The inlet area can be adjusted by moving the inlet guide vanes which subsequently control the velocity. When originally designed, the tunnel could produce velocities from 15 m/s to 48 m/s. However, the maximum velocity that can currently be reached is approximately 42 m/s. A honeycomb (8,000 cells, 76.2 mm thick) and 3 screens are installed in the 1.2 square meter settling section. This honeycomb helps to reduce the freestream turbulence level in the flow prior to entering the nozzle. The nozzle accelerates the flow and reduces the area of the tunnel from 0.836 m2 to 0.093 m2 , before the test section. This area reduction decreases the boundary layer thickness at the entrance of the test section. The exit of the tunnel is 12″ by 12″ and has a mounting flange at the exit.
A test section was constructed out of ½  » thick Lexan , a clear acrylic material. The inside dimensions of the test section was 12″ by 12″ to match the exit of the wind tunnel. The test section was 40 inches long and had a flange on one end to attach it to the wind tunnel exit. A ¼ » hole was cut 4 inches from the beginning that was used for a Pitot static probe used to measure the inlet conditions. Tests were run on single hinges and combinations of two hinges, positioned on top of each other and side to side. Three holes were drilled on either side of the test section to allow the rods to be placed so the different combinations of hinges could be tested. There were seven ¼ » inch slots cut across the width of the top of the test section. These slots were used for the Pitot probe to scan the area inside. The first slot was placed so that the sensing end of the probe was 1” behind the rod holding the hinge. The slots then continued every 2 inches downstream for a distance of 13 inches behind the hinge, for a total of seven slots. This would allow for measurements at 1,3,5,7,9,11,and 13 inches downstream of the airfoil. A picture of the test section and wind tunnel can be seen in Figure 3.4.
A traverse was used to allow the pitot tube to scan the entire section. This was a student-made traverse that was manually positioned. This traverse was located on top of the test section and the probe was fed through the slots that were cut there. The traverse could be moved from slot to slot to measure different downstream stations. This traverse was able to scan the entire area of the test section. The horizontal and vertical position of the probe could be set manually using two hand cranks. A picture of the traverse can be found in Figure 3.5.
There were two pressure probes used to collect data. A Pitot-static probe was used that was placed 4 inches from the inlet. This was used to capture the inlet conditions, including inlet total pressure and inlet differential pressure. There was also a Pitot probe attached to the traverse. This probe was used to capture the steady state total pressure in the wake behind the splitting airfoil. These pressure patterns were the focus of this study.
The probes were connected to a pressure transducer by flexible neoprene tubes. The transducer used was a Datametrics Barocel Type 590D-10W-2PI-V1X-4D that was capable of measuring differential pressures up to 10 inches of water. To get the differential pressure upstream the tubes from the pitot-static probe were attached to high and low ends of the pressure transducer. For the total pressure measurements, both probes were attached individually by tubes to the high pressure end and the were referenced to ambient pressure. The pressure transducer was linked to a Type 1400 Electronic Manometer that read in inches of water. This arrangement allowed pressure measurements accurate to 0.001 inches of water. The voltage from the manometer was input to a National Instruments Data Acquisition box that was linked to a laptop through a data acquisition card (type A1-16E-4). Labview software was used to analyze the transducer signal. The data acquisition system was set up to have a low pass Butterworth Filter with a cutoff frequency of 100 Hz . Data was collected at 10,000 scans/sec every 3 seconds. The output voltage from Labview was displayed on the laptop and the corresponding pressure values were input into a spreadsheet.

1 Introduction
2 Literature Review
2.1 Current Inlet Pressure Distortion Practice
2.2 Transient Distortion Considerations
2.3 Transient Distortion Generator Concept
2.4 Splitting Airfoil Tests Completed
3 Experimental Setup
3.1 Model Development
3.2 Wind Tunnel and Test Section
3.3 Testing Procedure
4 Test Results 
4.1 Flow Characteristics
4.2 Single Wedge Results
Total Pressure Loss Contours
Wake Width
Maximum Pressure Loss
Similarity Study
Summary
4.3 Horizontally Aligned Wedge Results
Total Pressure Loss Contours
Maximum Pressure Loss
Comparison with Single Wedge Data
Summary
4.4 Vertically Aligned Wedge Results
Total Pressure Loss Contours
Maximum Pressure Loss
Comparison with Single Wedge Data
Prediction of Combination Data
Summary
5 Conclusions and Recommendations 
5.1 Conclusions
5.2 Recommendations
References
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Study of Steady-State Wake Characteristics of Variable Angle Wedges

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