Norikazu Sudani

Test time increase by delaying driver gas contamination for reflected shock tunnels

A gasdynamical detectorhas been applied to measure thearrival timeof driver gas in a low concentration in the testsectionofa high-enthalpyshock tunnel. Thedetection determines theusefultesttimewith uncontaminated test gas for a wide range of specie c reservoir enthalpies. Effects of over- or undertailored interface condition on severe contaminationhavebeeninvestigated.Itisexperimentallydemonstratedthatovertailoredinterfaceoperationmust beavoided toachievethetestdurationnecessary foraerodynamicmeasurements,especially forhigh-enthalpy e ow. Theinterfacecondition isoptimized forthelongesttesttimeattainable. Asan activemethod fordelaying drivergas contamination,adevicetotrapthedrivergasattheendoftheshocktubehasbeentriedforanovertailoredcondition. The method, however, causes the contamination to occur earlier. A modie ed device using a sleeve to capture driver gas upstream has been developed. Results with the longest sleeve tested show that strong contamination is dramatically delayed and that the uncontaminated test time is signie cantly increased. Nevertheless, improved test times are still shorter than the test time without the device at a slightly undertailored condition.

Gasdynamical detectors of driver gas contamination in a high-enthalpy shock tunnel

Simple gasdynamical devices consisting of a duct and a wedge have been applied to the detection of driver gas arrival in the test section of a high-enthalpy shock tunnel. Static pressure in the duct has been measured during a shot, and the time of driver gas arrival has been determined by the onset of the pressure rise, which indicates duct flow choking. The ability to detect driver gas in small concentrations is critical to the satisfactory performance of the device. Duct internal flows for various wedge angles have been numerically simulated to clarify the flow choking mechanism. The simulations give an idea of the improvement of detector sensitivity, and modified configurations of the detector are proposed. Flow visualization in the duct leads to a better understanding of pressure traces obtained, and pressure measurement data show a satisfactory degree of sensitivity

Assessment of sidewall interference in a two-dimensional transonic wind tunnel

Effects of test section sidewalls have been investigated in a two-dimensional transonic wind tunnel. The facility has recently been modified to improve the flow two-dimensionality for airfoil testing. A procedure where two corrections for top and bottom wall interference and for sidewall interference are combined is applied to data obtained in the modified facility. Satisfactory agreement with free-air computations and other experimental results is presented for two different airfoils. The applicability of sidewall corrections to various configurations of airfoil model is then discussed. To reduce threedimensional effects, a device for removing sidewall boundary layers has been installed. The significant validity of the device, however, has not been confirmed because of Mach number nonuniformity. These results suggest that the optimum experimental arrangement for transonic airfoil testing should be reconsidered for each wind tunnel to provide truly two-dimensional data.

CELL STRUCTURE ON CIRCULAR CYLINDERS NEAR THE CRITICAL REYNOLDS NUMBER

Summary Flow visualization for two-dimensional circular cylinders and a conical blunted circular cylinder near the critical Reynolds number is shown. A circular cylinder 1.045m long 0.2 m in diameter at M=O.1-0.15 shows almost twodimensional bubbles and weak three-dimensional separation curves. Some of the turbulent wedges produced by discrete artificial roughness serve to create V-shaped dividing curves in the bubble and reattached region, however, others give no effect. A circular cylinder 0.2 m (0.3 m) long and 0.025 m in diameter at M=0.5 creates cell structure of separation line. As the Reynolds number increased these cell structures vanished. The conical blunted cone cylinder model shows two-dimensional and cell structured separation lines in the reattached region. Symbols cd = drag coefficient of cylinder per unit length lift coefficient of cylinder per unit length diameter of cylinder spin rate (Hz) length of cylinder Mach number critical Reynolds number (single bubble c, = d= f= 1=