The measurements will be conducted in the Matched-Index-of-Refraction (MIR) Facility at the Idaho National Engineering and Environmental Laboratory (INEEL), the largest MIR Facility in the world (Stoots et al., 2001). Optical flow measurement techniques, such as laser Doppler velocimetry (LDV) and Particle Tracking Velocimetry, permit flow field determination without locating transducers in the flow. By using transparent models, complex flow fields can be studied and the results can be used to assess the validity of computational fluid dynamic codes for difficult conditions. However, refraction of light beams can distort the views, introduce positioning errors and block measurements in some desired regions. A solution to these difficulties is to match the indices of refraction of the model and the fluid so that light rays are not deflected. While the INEEL MIR flow system has the refractive matching advantage that permits measurements that would otherwise be impossible, its innovation and technical significance is its large size. It is considerably larger than most other systems using the MIR technique; consequently, it provides significantly better spatial and temporal resolution at a given Reynolds number, typically by an order-of-magnitude.

The MIR flow system employs a light mineral oil as the working fluid. The current test section is 0.61 meters square and 2.4 meters long. Maximum design flow rate is about 0.35 cubic meters per second. Current instrumentation includes a two-component fiber optics LDV, a computer-controlled three-directional traversing mechanism, hot-film anemometers, a computer data acquisition system with LabView software and typical temperature and pressure sensors. A parallel auxiliary flow loop with an electric heater and a heat exchanger is employed with computer feedback control in order to maintain a selected, steady temperature in the system.

Maximum velocity in the current test section is about two meters per second. Qualification measurements with hot film sensors and with the LDV showed the free-stream velocity profile to be uniform to within one per cent and the free-stream turbulence level was 0.5 to 0.8 per cent without tripping. Fluid temperature is maintained to within 0.04 C to control its refractive index.

Additional photos of MIR Facility

Above is a schematic of the turbulence generator – it is an active grid of 21 parallel tubes that has been installed 5.1 cm upstream of the test section. The tubes are spaced on 2.54 cm centers (M = 2.54 cm) and have small holes on the upstream side of the array for secondary flow injection. Injection oil is provided through a parallel auxiliary flow loop powered by a separate pump. According to Welsh et al. (1997) and relationships developed by Roach (1987), this active grid should produce a free-stream turbulence intensity (Tu) of about 9-10% at the leading edge of the test plate (46 cm downstream from the turbulence generator). Also, in accordance with the findings of Blair (1982) and Young et al. (1992), the turbulence at 20 grid mesh lengths downstream (x/M=20) should be homogeneous. In the present apparatus the leading edge of the plate is located at x/M = 18.

Additional Photos of Turbulence Generator

The test plate and pressure gradient inserts are illustrated in figure above. The test plate is made of three sections of 1.3 cm thick aluminum plate and two sections of 1.3 cm thick GE124 clear fused quartz. The first section of the test plate is a 15.2 cm long with the leading edge machined into the shape of a NACA 009 airfoil. A turbulence trip is located 12.7 cm downstream of the leading edge. The trip consists of the four staggered rows of dowel pins across the plate. The trip was designed to simulate the boundary layer disturbances due to the film cooling jets that are located near the leading edge of a turbine blade. The quartz sections are installed so that they are centered in the glass windows of the test section. The top and bottom pressure gradient inserts are made of 1.3 cm thick aluminum plate and are placed in the test section to produce an acceleration parameter, K = (n/U¥ ²)(d U¥ /dx), of approximately 3 x 10^-6. Blair (1982, 1983), Keller and Wang (1996), Volino and Simon (1997), Zhou and Wang (1996) and others have conducted related boundary studies with K ranging from 0.2 x 10^-6 to 4.1 x 10^-6. The value in the present study, K = 3 x 10^-6, represents a typical dimensionless acceleration that is found on suction side of a turbine vane over the first one-quarter of the blade.

Additional photos of Test Plate Apparatus