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In the present study, no-load losses of different splash lubricated spiral bevel gears were measured. The authors used a specific test rig, and a set of gears, to investigate churning losses at higher tangential speeds: up to 60 m/s. An uncommon behavior of the drag torque was highlighted: the torque increased with the rotational speed until a local maximum was reached; then the torque decreased and a local minimum was noticed; at higher rotational speed the torque increased. The torque decrease seems to be linked with a windage phenomenon, which becomes non-negligible at such speeds. In this work, efforts were made to characterize this reduction of gear immersion depth in order to be able to predict no-load losses. It was found that the evolution of oil immersion was linked to a Froude number. Finally a new analytical model of no-load losses was developed for churning losses combined with windage effects. This formulation takes into account several parameters such as rotational speed, gear immersion depth, oil properties, and gear geometrical parameters.

In high-speed rolling element bearings, the drag forces can be prominent and it is demonstrated in this investigation that the classical models may not be appropriate for correctly estimating this ...

International audience; This article deals with the Windage Power Losses (WPL) of pinion-gear pairs rotating in air. The WPL of several disks, spur and helical gears have been measured using a dedicated test rig developed from a WPL measurement system initially used for one single pinion or disk. In practice, several gears are in mesh and the windage losses for coupled pinion-gear systems need to be addressed. It is experimentally confirmed that, although some couplings can be identified between two rotating gears, the total WPL can be estimated as the sum of that of each individual member.

Oil sump lubrication is commonly used in gearboxes. When considering consistent speeds, oil immersion is usually set to low level in order to reduce associated power losses. This configuration is already used in some parts of helicopter mechanical transmissions, and it is under consideration as a lubrication solution for future electric powertrain where gearbox input speeds may be very high. The gear drag power losses are generally evaluated from either a churning power loss model for classic oil sump lubrication or a windage power loss model for oil jet lubrication. One may thus wonder how to estimate drag losses when considering a gear that only a small part is immersed. In this study, the authors investigate the transition between churning and windage phenomena for a spur gear. A series of torque measurements on a single spur gear rotating in an oil bath at numerous oil immersion levels have been carried out. Based on these results, a criterion to indicate which power loss model to use is proposed.

This paper examines the use of proper orthogonal decomposition (POD) and singular value decomposition (SVD) to identify zones on the surface of the source that contribute the most to the sound power the source radiates. First, computational fluid dynamics (CFD) is used to obtain the pressure field at the surface of the blade in a subsonic regime. Then the fluctuation of this pressure field is used as the input for the loading noise in the Ffowcs Williams and Hawkings (FW&H) acoustic analogy. The FW&H analogy is used to calculate the sound power that is radiated by the blade. Secondly, the most important acoustic modes of POD and SVD are used to reconstruct the radiated sound power. The results obtained through POD and SVD are similar to the acoustic power directly obtained with the FW&H analogy. It was observed that the importance of the modes to the radiated sound power is not necessarily in ascending order (for the studied case, the seventh mode was the main contributor). Finally, maps of the most contributing POD and SVD modes have been produced. These maps show the zones on the surface of the blade, where the dipolar aeroacoustic sources contribute the most to the radiated sound power. These identifications are expected to be used as a guide to design and shape the blade surface in order to reduce its radiated noise.

This paper deals with recent experimental and numerical research in the possible reduction of windage power losses (WPL). It is accepted that these load-independent losses become prominent over other sources in mechanical transmissions with peripheral speeds above 100 m/s as is the case in energy production, aeronautics and electric vehicles. So far, the majority of the experiments and models deal with WPL evaluation for one single rotating pinion. The unique test rig designed at INSA Lyon makes it possible to measure both the WPL of a single pinion or a non-meshing pinion-gear pair. A number of comparisons between experimental and numerical results are presented and commented upon. It is shown, that the gear environment changes the airflow and, in depending on the cases, it can either reduce or increase WPL. Finally, the influence of pinion-gear couplings on WPL is discussed as well as the interest of shrouds and deflectors.

This paper examines the capability of both the Proper Orthogonal Decomposition (POD) and the Singular Value Decomposition (SVD) to identify the zones on the surface blades of a centrifugal fan that contribute the most to the sound power radiated by moving blades. The Computational Fluid Dynamics (CFD) OpenFOAM\(^{\textregistered }\) source code is used as a first step to evaluate the pressure field at the surface of the blade moving in a subsonic regime. The fluctuating component of this pressure field makes it possible to directly estimate both the loading noise and the sound power that is radiated by the blade based on an acoustic analogy of Ffowcs Williams and Hawkings (FW&H). In the second step, the estimated loading noise is then employed to evaluate the radiated sound power using the POD and SVD approaches. It may be noted that the sound power reconstructed by the two latter approaches, when relying solely on the most important acoustic modes, is similar to the one predicted by the FW&H analogy. It is also noted that the contribution of the modes in the radiated sound power does not necessarily appear in ascending order in the decomposition (i.e., in descending order of energy). Moreover, the highest radiating SVD modes are mapped onto the blade surface so as to highlight the zones that contribute the most to the noise. It is then expected that this identification will be used as a guide in the design of the blade surface to reduce the radiated noise.

International audience; Blood is a complex fluid in which the presence of the various constituents leads to significant changes in its rheological properties. Thus, an appropriate non-Newtonian model is advisable; and we choose a Modified version of the rheological model of Phan-Thien and Tanner (MPTT). The different parameters of this model, derived from the rheology of polymers, allow characterization of the non-Newtonian nature of blood, taking into account the behavior of red blood cells in plasma. Using the MPTT model that we implemented in the open access software OpenFOAM, numerical simulations have been performed on blood flow in the thoracic aorta for a healthy patient. We started from a patient-specific model which was constructed from medical images. Exiting flow boundary conditions have been developped, based on a 3-element Windkessel model to approximate physiological conditions. The parameters of the Windkessel model were calibrated with in vivo measurements of flow rate and pressure. The influence of the selected viscosity of red blood cells on the flow and wall shear stress (WSS) was investigated. Results obtained from this model were compared to those of the Newtonian model, and to those of a generalized Newtonian model, as well as to in vivo dynamic data from 4D MRI during a cardiac cycle. Upon evaluating the results, the MPTT model shows better agreement with the MRI data during the systolic and diastolic phases than the Newtonian or generalized Newtonian model, which confirms our interest in using a complex viscoelastic model.

International audience; This paper investigates the windage power losses generated by helical gears rotating in pure air based on experimental results and a computational fluid dynamic code. It is found that the simulated flow patterns are totally different from those calculated for spur gears and that both tooth face width and helix angle are influential. The windage losses derived from Dawson’s and Townsend’s formulae are critically assessed using computational fluid dynamic results thus highlighting the limits of a unique formulation for accurate windage loss prediction. Finally, an analytical approach is suggested which gives good results providing that the flow rates at the boundaries of the inter-tooth domains can be estimated.

In high-speed rolling element bearings the drag force generated by the motion of the balls in an air–oil mixture is frequently taken into account using the results for a sphere in an infinite medium. This approach is surprising because important interaction between the flows around the balls may occur. The drag coefficient value should be then adjusted to the configuration that is observed in a rolling element bearing (REB). In this article, a computational fluid dynamics code is applied to simulate three configurations: one single sphere, two spheres in tandem, and a set of spheres that are aligned along the air flow. It can be seen that both the flow pattern around one sphere and its drag coefficient are modified when placing another sphere in its vicinity. Furthermore, in REB configuration the drag coefficient value is far from the one observed when the obstacle is isolated and mainly depends on the space between the obstacles.

International audience; In this paper a computational fluid dynamics (CFD) code is applied to three-dimensional simulations of windage power loss generated by spur gears rotating in air. Emphasis is placed on the simplification which can be made in the numerical approach in order to gain cost and time needed for reaching a converged solution when using both fine mesh and important angular velocity. It appears that the similarity of the flows which are observed in the vicinity of both gear and disk sides is helpful. It is finally possible to compute the flow pattern near the teeth without simulating the contribution of the sides when appropriate boundary conditions are applied at the inlet of a truncated computational domain. The predictions of windage power losses using this original method are satisfying.

An investigation of heat transfer between a flow and a horizontal non-circular slender cylinder is presented in this article. Both experimental and numerical approaches are considered here. When using identical cylinders and free-stream velocities, a comparison between experimental data and numerical estimation emphasizes the shear stress transport k–ω turbulent model associated with fine mesh near wall to be appropriate for estimating an average value of heat transfer coefficient in the present configuration. From a numerical parametric investigation, which is based on the latter approach, two formulations of heat transfer are to be considered as thickness does not have a real influence in heat transfer for low Reynolds numbers, whereas for higher values, both thickness and width participate in heat transfer.

International audience; When considering high-speed gear transmission, the power loss due to the fluid drag torque generated by the gear rotation in air/oil mist may dominate the other losses. This windage power loss (WPL) must be therefore studied in order to mitigate its impact. Numerous investigations have been made in the past essentially to propose WPL model. However the influence of helix angle is not clearly understood since most of the previous studies considered spur gears. Experiments have still shown that WPL value is modified when helix angle value becomes not null. More investigations are therefore needed to reach appropriate model. The purpose of this paper is to build a numerical model using CFD method which is capable to estimate WPL generated by helical gears whose characteristics differ from their helix angle values. The helix angle influence is highlighted since both the volumetric flow rate which is expelled by the rotating gear and WPL are affected by a modification of this parameter.

International audience

International audience; This paper investigates the windage power losses generated by spur gears rotating in pure air by using a computational fluid dynamics (CFD) code. The three-dimensional simulations are at first validated comparing CFD predictions with the power losses measured in similar conditions from other investigations. The volumetric flow rate which is expelled by the teeth is then analysed, and a correlation which is based on a classical approach used in turbomachinery is finally proposed which makes it possible to estimate windage losses for spur gears. It was observed that this latter approach seems satisfying since the formulation of the volumetric flow rate which is employed in the model is appropriate to each gear.

International audience; In this paper, a computational fluid dynamics (CFD) code is applied to two- and three-dimensional simulations of windage power loss (WPL) generated by spur gears rotating in air. Emphasis is placed on the various meshes associated with the Finite Volume Method (FVM) and on the choice of turbulence model. Comparing CFD predictions with the power losses measured on a specific test rig, it is shown that the fluid ejection in the radial direction must be included in order to reproduce the experimental evidence. The relative importance of the losses generated by the gear front and rear faces along with those due to the teeth is discussed. The volumetric flow rate expelled by the teeth is analysed and the influence of flanges is highlighted.

National audience; Cette étude s'intéresse aux prédictions numériques des pertes par ventilation observées dans les transmissions par engrenages ayant des vitesses périphériques importantes. Le rôle du débit éjecté par les roues dentées testées est d'une part analysé et une formulation des pertes basée sur une analogie avec la cinématique de l'écoulement dans un système rotor est d'autre part proposée.

VDI-Berichte 2108-2; International audience

In this study a nonintrusive method for temperature measurement is investigated. The technique involves a two-beam schlieren system based on the measurement of angular beam dee ection across an axisymmetric e ow. The mean temperature is obtained by the Abel transform using the Gladstone approximation. Fluctuating temperatures are estimated by statistical processes of the beam dee ections. Validation is e rst performed in subsonic e ow, where schlieren data are compared with those obtained using classical probe. Finally, the schlieren method is successfully applied on supersonic jets approaching space launcher conditions. In the case of perfectly expanded jets, comparison between numerical and optical data shows good agreement. Nomenclature D = nozzle diameter, m J = Gladstone’ s constant, K LC = length of the potential core, m l = length scale, m M = Mach number n = refractive index P = pressure, Pa R = gas constant, J/mol ¢K r = radial component, m T = temperature, K V = jet velocity, m/s y = axial component, m ° = ratio of the specie c heats 2 = angle of beam dee ection, rad Ω = density, kg/m 3 ? = e uctuation rate of temperature Subscripts a = ambient condition i = stagnation condition j = perfectly expanded condition o = centerline component s = static component t = transverse component Superscripts N = time average 0 = e uctuating component

The effects of temperature both on supersonic jet noise with water injection (used for noise reduction) and on the efficiency of the method are investigated. The location of injection varies from 1.5D to 15D while the other parameters remain fixed to their optimum values. One notices better overall noise level reductions by injecting close to the nozzle exit. Moreover spectral analysis emphasizes that attenuation in high and low frequencies depends on the location of injection. Finally, the jet temperature does not greatly affect the efficiency of this method as the measured attenuation is similar to that encountered with supersonic jets with ambiant temperature. To cite this article: Y. Marchesse et al., C. R. Mecanique 330 (2002) 1–8

International audience

International audience

Colloque avec actes et comité de lecture. Internationale.; International audience; Cette étude s'intéresse aux prédictions numériques basées sur la méthode RANS des pertes par ventilation observées dans les systèmes de transmission à engrenages ayant des vitesses périphériques importantes. Le rôle du débit éjecté par les roues dentées testées est d'une part analysé et une formulation des pertes basée sur une analogie avec la cinématique de l'écoulement dans un système rotor est d'autre part proposée.

International audience

International audience

International audience; This paper investigates the windage power loss generated by helical gears rotating in pure air. A three-dimensional approach using computational fluid dynamics (CFD) code which has been validated for spur gear is adapted here in order to consider helix angle. The numerical approach is at first validated with the power losses measured in similar conditions. The influence of both width and helix angle values on the expelled volumetric flow rate and the windage losses are studied. Considering these observations, a correlation which is based on a classical approach used in turbomachinery is proposed.