A Compressible Turbulence Model for Pressure—Strain

This work focuses on the performance and validation of compressible turbulence models for the pressure-strain correlation. Considering the Launder Reece and Rodi (LRR) incompressible model for the pressure-strain correlation, Adumitroaie et al., Huang et al., and Marzougui et al., used different modeling approaches to develop turbulence models, taking into account compressibility effects for this term. Two numerical coefficients are dependent on the turbulent Mach number, and all of the remaining coefficients conserve the same values as in the original LRR model. The models do not correctly predict the compressible turbulence at a high-speed shear flow. So, the revision of these models is the major aim of this study. In the present work, the compressible model for the pressure-strain correlation developed by Khlifi−Lili, involving the turbulent Mach number, the gradient, and the convective Mach numbers, is used to modify the linear mean shear strain and the slow terms of the previous models. The models are tested in two compressible turbulent flows: homogeneous shear flow and the newly developed plane mixing layers. The predicted results of the proposed modifications of the Adumitroaie et al., Huang et al., and Marzougui et al., models and of its universal versions are compared with direct numerical simulation (DNS) and experiment data. The results show that the important parameters of compressibility in homogeneous shear flow and in the mixing layers are well predicted by the proposal models.

Properties of the compressibility and transport motion in wall-bounded turbulent flows at Mach 8

The compressibility effect and transport motion in highspeed turbulent boundary layer (TBL) is a fundamental problem because they dominate the average and statistical characteristics. Using the statistical methods and flow visualization technology, flat-plate TBLs at [Formula: see text] with high- and low-wall temperatures, [Formula: see text] and 1.9, are investigated based on the direct numerical simulation (DNS) datasets. Compared with previous studies, this study considers relative higher Mach number and strong cold wall temperature condition at the same time. First, the turbulent Mach number and turbulent intensity show that the compressibility effects are enhanced by the cooling process. Second, the high-order statistical moments and structure parameters confirm cold wall that causes stronger compressibility and the corresponding increased intensities of local streamwise and wall-normal transport motions. Finally, for uncovering the relationship between the compressibility effect and turbulent transport, more in-depth visualization analyses of velocity streaks are performed. It is found that ‘knot-like’ structures are generated when cooling the wall, and they lead to stronger intermittent, which results in the rapid increase of local compressibility effect and the wall-normal transport motion. Our research sheds light on providing a theoretical basis for further understanding the compressibility effects of TBL at high Mach number.

Measurement of Heat Transfer and Flow Structures in a Closed Rotating Cavity

Buoyancy-induced flow occurs inside the rotating compressor cavities of gas turbines. These cavities are usually open at the inner radius, but in some industrial gas turbines, they are effectively closed. This paper presents measurements of the disc heat transfer and rotating flow structures in a closed cavity over a wide range of engine relevant conditions. These experimentally derived distributions of disc temperature and heat flux are the first of their kind to be published. The radial distribution of the non-dimensional disc temperature virtually collapsed onto a single curve over the full experimental range. There was a small, monotonic departure from this common curve with increasing Reynolds number; this was attributed to compressibility effects where the core temperature increases as the rotational speed increases. These results imply that, if compressibility effects are negligible, all rotating closed cavities should have a disc temperature distribution uniquely related to the geometry and disc material; this is of important practical use to the engine designer. Unsteady pressure sensors detected either three or four vortex pairs across the experimental range. The number of pairs changed with Grashof number, and the structures slipped relative to the rotating discs by less than 1% of the disc speed.

Estimación de la Eficiencia de una Hélice Operando en Régimen Compresible Subsónico

La información experimental disponible para hélices no es útil cuando el número de Mach de la punta de la pala es mayor a . Con el fin de verificar esta aseveración, se propuso un caso de estudio para una hélice Navy 5868-9 con perfil aerodinámico Clark-Y de 4 palas operando a un número de Mach de avance de 0.59 y un número de Mach en la punta de la pala de 0.95. La eficiencia experimental de la hélice (obtenida de gráficas) se compara con la eficiencia obtenida empleando la teoría combinada y con la eficiencia obtenida al corregir la teoría combinada por efectos de compresibilidad con la metodología propuesta en este trabajo. Se concluye que la información experimental disponible para hélices no es adecuada cuando el número de Mach en la punta de la pala es mayor que el Mach crítico, siendo más conveniente el resultado teórico corregido por compresibilidad. The experimental information available for propellers is not useful when the Mach number of the tip of the blade is greater than 0.3. In order to verify this assertion, a case study was proposed for a Navy propeller 5868-9 with a 4-blade Clark-Y airfoil section operating at an advance Mach number of 0.59 and a Mach number at the tip of the blade of 0.95. The experimental efficiency of the propeller (obtained from graphs) is compared with the efficiency obtained using the combined theory and with the efficiency obtained by correcting the combined theory for compressibility effects with the methodology proposed in this paper. It is concluded that the experimental information available for propellers is not suitable when the Mach number at the tip of the blade is greater than the critical Mach, being more convenient the theoretical result corrected by compressibility.