Abstract. An experimental investigation of the propagation of turbulent spots occurring naturally during boundarylayer transition was conducted. Wide-bandwidth heat-transfer instrumentation was used in tracking individual turbulent spots as they progressed down a flat-plate surface toward fully-developed turbulence. The convection rates of the turbulent/non-turbulent interfaces of the spots in the streamwise direction were determined, as were rates of lateral spreading. The separate effects of compressibility and favourable pressure gradients have been assessed, and some typical results have been reported. List of symbols

The effect of the interaction of the wake from a nozzle guide vane with the rotor may be simulated in part by means of a stationary rotor and a moving wake system. This technique is applied to a transonic rotor blade cascade, and the unsteady measurements of surface pressure and heat transfer rate are compared with baseline data obtained without the wake interaction. The wake-rotor interaction results in a change in inlet incidence angle and this effect is also examined in the steady-state case. It is found that the shock waves from the moving wake system have a major effect on the instantaneous heat transfer rates.

Heat transfer measurements have been made on a transonic turbine blade undergoing natural transition and with a simulation of the effect of NGV wake interactions. The use of wide bandwidth heat transfer instrumentation permits the tracking of individual unsteady events that were identified as being due to either the impinging wakes or to the turbulent spots occurring within the transition process. Trajectories of these events as seen by the blade surface instrumentation have been measured. Numerical models have been developed for the effects of both types of turbulent activity. The convection of the wake through the passage is predicted, allowing for estimations of the expected times for which the boundary layer is disturbed by the wake fluid. The new model for the random generation and subsequent growth and convection of the turbulent spots produces a time-resolved prediction of the intermittent heat transfer signals by use of a time-marching procedure. By superimposing the two numerical models it is possible to simulate the measured instantaneous heat transfer characteristics.

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110deg and blade chord of 1.0m. Data were obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0×105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle image velocimetry was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip end-wall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the undertip flow near the end wall due to the moving wall is observed and the effect on the tip leakage vortex examined.

Ultraviolet absorption and mass-spectrometric observations of shocked C2F4–Ar gas mixtures have indicated that the C2F4 monomer exists in thermal equilibrium with CF2 radicals and that the initial C2F4 oxidation mechanism involves two steps C2F4→ lim Ar2CF2CF2+O2→CO+2F+O.Dissociation and oxidation rates were determined from uv absorption measurements of CF2 at 2536 Å behind incident shock waves. The C2F4 dissociation reaction appeared to be second order, 12d[CF2]/dt=kAr[C2F4][Ar], with kAr=7.82×1015T12 exp(−55 690/RT) cc/mole·secover the temperature interval from 1200° to 1800°K at total concentrations between 0.9×10−5 and 1.7×10−5. A least-squares fit to the experimental equilibrium constants for the reaction C2F4=2CF2, using the integrated form of the van't Hoff equation, yielded logKc=−69 432/2.303RT+4.62 (Kc in mole/cc).From the measured heat of reaction, the heat of formation of CF2 at 298°K was calculated to be −39.7±3.0 kcal/mole. Mixtures of C2F4 and O2 in varying mole ratios were allowed to react at temperatures between 1500° to 2500°K with molar concentrations of reactants ranging from 4×10−8 to 6×10−7 mole/cc. The oxidation reaction was observed to be first order in both CF2 and O2, d[CF2]/dt=−kox[CF2][O2], with kox=2.92×1010T12 exp(−13 280/RT) cc/mole·sec.