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

2021 ◽  
Vol 2 (5) ◽  
pp. 6359-6370
Author(s):  
Tiburcio Fernández Roque ◽  
José Arturo Correa Arredondo ◽  
José Félix Vázquez Flores ◽  
Jorge Sandoval Lezama ◽  
Alejandro Mejía Carmona
Keyword(s):  
Mach Number ◽  
Theoretical Result ◽  
Experimental Information ◽  
Airfoil Section ◽  
Compressibility Effects

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.  

Compressibility effects in a turbulent annular mixing layer. Part 1. Turbulence and growth rate

2000 ◽  
Vol 421 ◽  
pp. 229-267 ◽  
Author(s):  
JONATHAN B. FREUND ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Growth Rate ◽  
Mach Number ◽  
Mixing Layer ◽  
Mixing Layers ◽  
Velocity Difference ◽  
Mean Velocity ◽  
The Mean ◽  
Mach Numbers ◽  
High Mach ◽  
Compressibility Effects

This work uses direct numerical simulations of time evolving annular mixing layers, which correspond to the early development of round jets, to study compressibility effects on turbulence in free shear flows. Nine cases were considered with convective Mach numbers ranging from Mc = 0.1 to 1.8 and turbulence Mach numbers reaching as high as Mt = 0.8.Growth rates of the simulated mixing layers are suppressed with increasing Mach number as observed experimentally. Also in accord with experiments, the mean velocity difference across the layer is found to be inadequate for scaling most turbulence statistics. An alternative scaling based on the mean velocity difference across a typical large eddy, whose dimension is determined by two-point spatial correlations, is proposed and validated. Analysis of the budget of the streamwise component of Reynolds stress shows how the new scaling is linked to the observed growth rate suppression. Dilatational contributions to the budget of turbulent kinetic energy are found to increase rapidly with Mach number, but remain small even at Mc = 1.8 despite the fact that shocklets are found at high Mach numbers. Flow visualizations show that at low Mach numbers the mixing region is dominated by large azimuthally correlated rollers whereas at high Mach numbers the flow is dominated by small streamwise oriented structures. An acoustic timescale limitation for supersonically deforming eddies is found to be consistent with the observations and scalings and is offered as a possible explanation for the decrease in transverse lengthscale.

scholarly journals The onset of compressibility effects for aerofoils in ground effect

2007 ◽  
Vol 111 (1126) ◽  
pp. 797-806 ◽  
Author(s):  
G. Doig ◽  
T. J. Barber ◽  
E. Leonardi ◽  
A. J. Neely
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Subsonic Flow ◽  
Flow Characteristics ◽  
Ground Effect ◽  
Aerodynamic Performance ◽  
Computational Studies ◽  
Pressure Gradients ◽  
Cfd Simulations ◽  
Compressibility Effects

Abstract The influence of flow compressibility on a highly-cambered inverted aerofoil in ground effect is presented, based on two-dimensional computational studies. This type of problem has relevance to open-wheel racing cars, where local regions of high-speed subsonic flow form under favourable pressure gradients, even though the maximum freestream Mach number is typically considerably less than Mach 0·3. An important consideration for CFD users in this field is addressed in this paper: the freestream Mach number at which flow compressibility significantly affects aerodynamic performance. More broadly, for aerodynamicists, the consequences of this are also considered. Comparisons between incompressible and compressible CFD simulations are used to identify important changes to the flow characteristics caused by density changes, highlighting the inappropriateness of incompressible simulations of ground effect flows for freestream Mach numbers as low as 0·15.

Theory of low Mach number compressible flow in a channel

1996 ◽  
Vol 313 ◽  
pp. 131-145 ◽  
Author(s):  
A. Shajii ◽  
J. P. Freidberg
Keyword(s):  
Steady State ◽  
Mach Number ◽  
Aspect Ratio ◽  
Compressible Flow ◽  
Applied Pressure ◽  
Subsonic Flows ◽  
Low Mach Number ◽  
Large Channel ◽  
Channel Aspect Ratio ◽  
Compressibility Effects

The properties of a relatively uncommon regime of fluid dynamics, low Mach number compressible flow are investigated. This regime, which is characterized by an exceptionally large channel aspect ratio L/d ∼ 106 leads to highly subsonic flows in which friction dominates inertia. Even so, because of the large aspect ratio, finite pressure, temperature, and density gradients are required, implying that compressibility effects are also important. Analytical results are presented which show, somewhat unexpectedly, that for forced channel flow, steady-state solutions exist only below a critical value of heat input. Above this value the flow reverses against the direction of the applied pressure gradient causing fluid to leave both the inlet and outlet implying that the related concepts of a steady-state friction factor and heat transfer coefficient have no validity.

scholarly journals Effect of compressibility on the global stability of axisymmetric wake flows

2010 ◽  
Vol 660 ◽  
pp. 499-526 ◽  
Author(s):  
P. MELIGA ◽  
D. SIPP ◽  
J.-M. CHOMAZ
Keyword(s):  
Mach Number ◽  
Base Flow ◽  
Sensitivity Analyses ◽  
Global Instability ◽  
Linear Dynamics ◽  
Wake Flows ◽  
Sensitivity Functions ◽  
Flow Profiles ◽  
Subsonic Regime ◽  
Compressibility Effects

We study the linear dynamics of global eigenmodes in compressible axisymmetric wake flows, up to the high subsonic regime. We consider both an afterbody flow at zero angle of attack and a sphere, and find that the sequence of bifurcations destabilizing the axisymmetric steady flow is independent of the Mach number and reminiscent of that documented in the incompressible wake past a sphere and a disk (Natarajan & Acrivos, J. Fluid Mech., vol. 254, 1993, p. 323), hence suggesting that the onset of unsteadiness in this class of flows results from a global instability. We determine the boundary separating the stable and unstable domains in the (M, Re) plane, and show that an increase in the Mach number yields a stabilization of the afterbody flow, but a destabilization of the sphere flow. These compressible effects are further investigated by means of adjoint-based sensitivity analyses relying on the computation of gradients or sensitivity functions. Using this theoretical formalism, we show that they do not act through specific compressibility effects at the disturbance level but mainly through implicit base flow modifications, an effect that had not been taken into consideration by previous studies based on prescribed parallel base flow profiles. We propose a physical interpretation for the observed compressible effects, based on the competition between advection and production of disturbances, and provide evidence linking the stabilizing/destabilizing effect observed when varying the Mach number to a strengthening/weakening of the disturbance advection mechanism. We show, in particular, that the destabilizing effect of compressibility observed in the case of the sphere results from a significant increase of the backflow velocity in the whole recirculating bubble, which opposes the downstream advection of disturbances.

Compressibility effects on the structural evolution of transitional high-speed planar wakes

2016 ◽  
Vol 796 ◽  
pp. 5-39 ◽  
Author(s):  
Jean-Pierre Hickey ◽  
Fazle Hussain ◽  
Xiaohua Wu
Keyword(s):  
Mach Number ◽  
Linear Stability ◽  
High Speed ◽  
Three Dimensional ◽  
Structural Evolution ◽  
Base Flow ◽  
Length Scale ◽  
Two Dimensional ◽  
Linear Mode ◽  
Compressibility Effects

The compressibility effects on the structural evolution of the transitional high-speed planar wake are studied. The relative Mach number ($Ma_{r}$) of the laminar base flow modifies two fundamental features of planar wake transition: (i) the characteristic length scale defined by the most unstable linear mode; and (ii) the domain of influence of the structures within the staggered two-dimensional vortex array. Linear stability results reveal a reduced growth (approximately 30 % reduction up to $Ma_{r}=2.0$) and a quasilinear increase of the wavelength of the most unstable, two-dimensional instability mode (approximately 20 % longer over the same $Ma_{r}$ range) with increasing $Ma$. The primary wavelength defines the length scale imposed on the emerging transitional structures; naturally, a longer wavelength results in rollers with a greater streamwise separation and hence also larger circulation. A reduction of the growth rate and an increase of the principal wavelength results in a greater ellipticity of the emerging rollers. Compressibility effects also modify the domain of influence of the transitional structures through an increased cross-wake and inhibited streamwise communication as characteristic paths between rollers are deflected due to local $Ma$ gradients. The reduced streamwise domain of influence impedes roller pairing and, for a sufficiently large relative $Ma$, pairing is completely suppressed. Thus, we observe an increased two-dimensionality with increasing Mach number: directly contrasting the increasing three-dimensional effects in high-speed mixing layers. Temporally evolving direct numerical simulations conducted at $Ma=0.8$ and 2.0, for Reynolds numbers up to 3000, support the physical insight gained from linear stability and vortex dynamics studies.

Are there thermoregulatory constraints on the timing of pupping for harbour seals?

1998 ◽  
Vol 76 (12) ◽  
pp. 2245-2254 ◽  
Author(s):  
A T Hind ◽  
WSC Gurney
Keyword(s):  
Metabolic Rate ◽  
Indirect Evidence ◽  
Minimum Cost ◽  
Experimental Information ◽  
Energetic Cost ◽  
Detailed Model ◽  
Harbour Seals ◽  
Seal Population ◽  
Moray Firth

In this paper we describe a detailed model of the thermal balance of a seal in air. We tested the model against the limited experimental information available on thermoregulation for harbour seals (Phoca vitulina) in air. Since a mother must meet both her own and her pups' energetic costs, we suggest that there may be an energetic advantage for harbour seals in Scotland if lactation is timed to coincide with the most favourable conditions for hauling out. To test this hypothesis, we used the harbour seals in the Moray Firth as our case study. The model does predict an energetic cost resulting from thermoregulation during haul-out for a mother and her pup in the Moray Firth. Taking the mother and pup as a unit, we estimate the minimum cost during lactation. This combined cost, which must be met by the female seal, is similar to the minimum metabolic rate during haul-out for the summer predicted from the model. In winter the predicted minimum metabolic rate exceeds the lactation cost, and an additional cost of thermoregulation results. The model predicts the most energetically favourable time for lactation to be June and July, and this is coincident with the timing of pupping in this seal population. We suggest that for harbour seals in Scotland, the timing of pupping may be influenced by the thermoregulation costs of haul-out. This provides indirect evidence that thermoregulation influences haul-out behaviour in this small phocid species.

scholarly journals A Compressible Turbulence Model for Pressure—Strain

Fluids ◽  
2022 ◽  
Vol 7 (1) ◽  
pp. 34
Author(s):  
Hechmi Khlifi ◽  
Adnen Bourehla
Keyword(s):  
Mach Number ◽  
Shear Flow ◽  
Turbulent Flows ◽  
High Speed ◽  
Turbulence Models ◽  
Mixing Layers ◽  
Compressible Turbulence ◽  
Homogeneous Shear ◽  
Homogeneous Shear Flow ◽  
Compressibility Effects

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.

A Variational Formulation of the Compressible Throughflow Problem

1976 ◽  
Vol 98 (1) ◽  
pp. 1-8 ◽  
Author(s):  
G. C. Oates ◽  
C. J. Knight ◽  
G. F. Carey
Keyword(s):  
Finite Element ◽  
Mach Number ◽  
Variational Formulation ◽  
Finite Element Approximation ◽  
Element Approximation ◽  
Natural Conditions ◽  
Viscous Forces ◽  
Algebraic Problem ◽  
Compressibility Effects ◽  
Highly Loaded

A variational formulation of the compressible throughflow problem is developed. The method is suitable for the calculation of throughflow flow fields in which large rotational effects, large compressibility effects and large variations in hub and tip radii may exist. The formulation requires the absence of viscous forces between the blade rows, though the effects of losses within the blade rows may be included through the variation of entropy across stream surfaces. The meridional Mach number is restricted to be less than unity, though the complete flow Mach number may be much in excess of unity. The variational formulation represents a complete statement of the problem in that the boundary conditions, far upstream and far downstream conditions, and matching conditions at all actuator disks are all natural conditions of the variational formulation. Furthermore, terms involving density variations vanish. The variational problem is posed in terms of the streamline position and the density. A finite element approximation produces a coupled nonlinear algebraic problem for numerical solution. Example calculations of flows with highly-loaded actuator disks, existing in annuli with large variations in hub and tip radii, are given.

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