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Uncertainty analysis of hot-wire data in turbulent flows are made for time-averaging and real-time data reduction techniques. Equations of uncertainty are derived in general form for every step of data taking and evaluation. Numerical examples are supplied for two-dimensional flat plate boundary layer data. Results show that the real-time data reduction techniques generally have a lower and much more uniform uncertainty distribution than the time-averaging techniques (whose uncertainties are much higher for the near-wall data).

a b s t r a c tThis paper presents the development and validation of a new partially-averaged Navier-Stokes (PANS) model which can successfully predict turbulent swirling flow with vortex breakdown. The proposed PANS model uses an extended low Reynolds number k-e model as the baseline model. Furthermore, a new formulation for the unresolved-to-total turbulent kinetic energy ratio f k is developed using partial integration of the complete turbulence energy spectrum. Therefore, the present formulation of f k is believed to be superior to the previously used constant or computed values. The newly developed PANS model is used in unsteady numerical simulations of two turbulent swirling flows containing vortex breakdown, namely swirling flow through an abrupt expansion and flow in a draft tube of a hydraulic turbine operating under partial load. The present PANS model accurately predicts time-averaged and root-mean-square (rms) velocities in the case of the abrupt expansion, while it is shown to be superior to the Delayed Detached Eddy Simulation (DDES) and Shear Stress Transport (SST) k-x models. Predictions of the reattachment length using the present model shows at least 14% and 23% improvements compared to the DDES and the SST k-x models respectively. Also, transient features of the flow, e.g. vortex rope formation and precession, is well captured in the case of the complex draft tube flow. The frequency of the vortex rope precession, which causes severe fluctuations and vibrations, is well predicted by only 7% deviations from the experimental data.

Numerical simulations and analysis of the vortex rope formation in a simplified draft tube of a model Francis turbine are carried out in this paper, which is the first part of a two-paper series. The emphasis of this part is on the simulation and investigation of flow using different turbulence closure models. Two part-load operating conditions with same head and different flow rates (91% and 70% of the best efficiency point (BEP) flow rate) are considered. Steady and unsteady simulations are carried out for axisymmetric and three-dimensional grid in a simplified axisymmetric geometry, and results are compared with experimental data. It is seen that steady simulations with Reynolds-averaged Navier–Stokes (RANS) models cannot resolve the vortex rope and give identical symmetric results for both the axisymmetric and three-dimensional flow geometries. These RANS simulations underpredict the axial velocity (by at least 14%) and turbulent kinetic energy (by at least 40%) near the center of the draft tube, even quite close to the design condition. Moving farther from the design point, models fail in predicting the correct levels of the axial velocity in the draft tube. Unsteady simulations are performed using unsteady RANS (URANS) and detached eddy simulation (DES) turbulence closure approaches. URANS models cannot capture the self-induced unsteadiness of the vortex rope and give steady solutions while DES model gives sufficient unsteady results. Using the proper unsteady model, i.e., DES, the overall shape of the vortex rope is correctly predicted and the calculated vortex rope frequency differs only 6% from experimental data. It is confirmed that the vortex rope is formed due to the roll-up of the shear layer at the interface between the low-velocity inner region created by the wake of the crown cone and highly swirling outer flow.

The effects of an acoustic field on the enhancement of coal combustion are investigated. A flat flame burner using methane-air mixtures as the fuel is used for the experiments. Micronized coal particles 20–70 μm in diameter are injected into the burning gas stream at the same velocity as the gas. The light intensity emitted from the flame, temperature and pictures of the flame with and without an acoustic field are recorded. The nominal values of the intensity of the acoustic field are between 140–160 dB and the frequency is between 500–3500 Hz. A definite increase in the rate of combustion of the coal particles is observed with the application of an acoustic field. The enhancement can be seen from the increased light intensity of the flame and the flame width. This paper presents the data and a discussion of light intensity emitted by the flame as a function of acoustic parameters.

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Hydrodynamic measurements were made with a triaxial hot wire in the full-coverage region and the recovery region following an array of injection holes inclined downstream, at 30° to the surface. The data were taken under isothermal conditions at ambient temperature and pressure for two blowing ratios: M = 0·9 and M = 0·4. (The ratio M = ρjetUjet/ρ∞U∞, where U is the mean velocity and ρ is the density. Subscripts jet and ∞ stand for injectant and free stream, respectively.) Profiles of the three mean-velocity components and the six Reynolds stresses were obtained at several spanwise positions at each of five locations down the test plate.In the full-coverage region, high levels of turbulence kinetic energy (TKE) were found for low blowing and low TKE levels for high blowing. This observation is especially significant when coupled with the fact that the heat transfer coefficient is high for high blowing, and low for low blowing. This apparent paradox can be resolved by the hypothesis that entrainment of the mainstream fluid must be more important than turbulent mixing in determining the heat transfer behaviour at high blowing ratios (close to unity).In the recovery region, the flow can be described in terms of a two-layer model: an outer boundary layer and a two-dimensional inner boundary layer. The inner layer governs the heat transfer.