Experimental and Numerical Investigation on Windage Power Losses in High Speed Gears

2017 ◽  
Author(s):  
D. Massini ◽  
T. Fondelli ◽  
A. Andreini ◽  
B. Facchini ◽  
L. Tarchi ◽  
...  
Keyword(s):  
High Speed ◽  
Power Transmission ◽  
Fluid Dynamic ◽  
Spur Gear ◽  
Cooling Capacity ◽  
Relative Magnitude ◽  
Power Losses ◽  
Test Rig ◽  
Aero Engines ◽  
Cooling And Lubrication

Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. The transmission system in fact has a direct impact on the engine overall efficiency by means of its weight contribution, internal power losses and lubrication requirements. Thus, an evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Gears are among the most efficient power transmission systems, whose efficiencies can exceed 99 %, nevertheless in high speed applications power losses are anything but negligible. All power dissipated through losses is converted into heat that must be dissipated by the lubrication system. More heat leads to a larger cooling capacity, which results in more oil, larger heat exchangers which finally means more weight. Mechanical power losses are usually distinguished in two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid-dynamics of the environment which surrounds the gears, namely windage, fluid trapping and squeezing between meshing gear teeth and inertial losses resulting by the impinging oil jets, usually adopted in high speed transmission for cooling and lubrication purposes. The relative magnitude of these phenomena is strongly dependent on the operative conditions of the transmission. While load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. Among fluid-dynamic losses, windage is extremely important and can dominate the other mechanisms. In this context, a new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry measurements for investigating the flow-field surrounding the rotating gear. The experiment has been computationally replicated, performing RANS simulations in the context of conventional eddy viscosity models. The numerical results were compared with experimental data in terms of resistant torque as well as PIV measurements, achieving a good agreement for all of the speed of rotations.

Experimental and Numerical Investigation on Windage Power Losses in High Speed Gears

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Daniele Massini ◽  
Tommaso Fondelli ◽  
Antonio Andreini ◽  
Bruno Facchini ◽  
Lorenzo Tarchi ◽  
...  
Keyword(s):  
High Speed ◽  
Spur Gear ◽  
Relative Magnitude ◽  
Navier Stokes ◽  
Power Losses ◽  
Test Rig ◽  
Viscosity Models ◽  
Image Velocimetry ◽  
And Performance ◽  
Aero Engines

Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. An evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Mechanical power losses are usually distinguished into two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid dynamics of the environment, which surrounds the gears. The relative magnitude of these phenomena is dependent on the operative conditions of the transmission: load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. A new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry (PIV) measurements for investigating the flow field surrounding the rotating gear. The experiment has been computationally replicated, performing Reynolds-averaged Navier–Stokes (RANS) simulations in the context of conventional eddy viscosity models, achieving good agreement for all of the speed of rotations.

Fuel Consumption Reduction of Off-Road Vehicles by Improving the Efficiency of the Hydromechanical Variable Transmission’s Lubrication and Actuation Systems

2020 ◽  
Author(s):  
Massimo Milani ◽  
Luca Montorsi ◽  
Stefano Terzi ◽  
Gelmini Mario ◽  
Fabrizio Panizzolo ◽  
...  
Keyword(s):  
High Speed ◽  
Ad Hoc ◽  
Dynamic Models ◽  
Power Transmission ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Hydrodynamic Resistance ◽  
Power Losses ◽  
Relief Valve ◽  
Actuation System

Abstract The paper investigates the efficiency of a hydro-mechanical variable transmission combining experimental and numerical approaches in order to develop operating strategies for power transmission losses reduction due to hydraulic circuits design. Two operating regions, characterized by high working time, have been detected analyzing the telescopic boom handler load spectral map of a real off-road vehicle transmission; the first one characterized by high output speed and the second one by low speed and torque transmission. The efficiency of the former region has been increased by improving the fluid dynamic behavior of the lubrication system, which is greatly affected by the high flow rate generated by the fixed displacement pump operating at high speed, while the latter has been improved regulating the flow pressure of the actuation system with a controlled relief valve. The power losses of the system are experimentally determined testing an instrumented transmission on an ad-hoc test rig. CFD dynamic models are adopted for the lubrication circuit optimization, addressing its real geometrical features as well as the actual operating conditions. Furthermore, the influence of the hydrodynamic resistance of the reverse and first wet clutches on the transmission power losses is investigated regulating the lubrication flow through an on/off valve. Tests demonstrated that up to 6.5 kW can be saved at high transmission ratios. Finally, the effect of the two regulating strategies have been estimated in terms of energy saving and C02 emission reduction on the total vehicle life. Results proved that 5600 kWh and 7250 kWh saved energy can be achieved for the two strategies corresponding to 3.7 tons and 4.6 tons of avoided CO2 respectively.

Three-Dimensional CFD Analysis of Meshing Losses in a Spur Gear Pair

2018 ◽  
Author(s):  
T. Fondelli ◽  
D. Massini ◽  
A. Andreini ◽  
B. Facchini ◽  
F. Leonardi
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Spur Gear ◽  
Computational Domain ◽  
Gear Pair ◽  
Transient Pressure ◽  
Numerical Effort ◽  
Free Environment

The reduction of fluid-dynamic losses in high speed gearing systems is nowadays increasing importance in the design of innovative aircraft propulsion systems, which are particularly focused on improving the propulsive efficiency. Main sources of fluid-dynamic losses in high speed gearing systems are windage losses, inertial losses resulting by impinging oil jets used for jet lubrication and the losses related to the compression and the subsequent expansion of the fluid trapped between gears teeth. The numerical study of the latter is particularly challenging since it faces high speed multiphase flows interacting with moving surfaces, but it paramount for improving knowledge of the fluid behavior in such regions. The current work aims to analyze trapping losses in a gear pair by means of three-dimensional CFD simulations. In order to reduce the numerical effort, an approach for restricting computational domain was defined, thus only a portion of the gear pair geometry was discretized. Transient calculations of a gear pair rotating in an oil-free environment were performed, in the context of conventional eddy viscosity models. Results were compared with experimental data from the open literature in terms of transient pressure within a tooth space, achieving a good agreement. Finally, a strategy for meshing losses calculation was developed and results as a function of rotational speed were discussed.

Experimental Investigation on Effusion Liner Geometries for Aero-Engine Combustors: Evaluation of Global Acoustic Parameters

2012 ◽  
Author(s):  
A. Andreini ◽  
B. Facchini ◽  
L. Ferrari ◽  
G. Lenzi ◽  
F. Simonetti ◽  
...  
Keyword(s):  
Cooling System ◽  
Fluid Dynamic ◽  
Pressure Fluctuations ◽  
Main Concern ◽  
Dynamic Features ◽  
Ambient Conditions ◽  
Test Rig ◽  
Acoustic Parameters ◽  
Field Range ◽  
Aero Engines

In new generation aero-engines based on the innovative lean combustion technology, thermoacoustic instabilities are one of the most important issues and their prevention and reduction are challenging goals. To achieve these targets, the use of multi-perforated liners, that have to primarily provide an efficient liner cooling, is very attractive because they are efficient passive dampers of pressure fluctuations, especially with bias flow. The design of multi-perforated liners for both thermal and acoustic purposes can be accomplished by selecting liner parameters, such as hole diameter, pattern and inclination, main and bias Mach numbers, fulfilling both requirements; this procedure requires to assess the effect of both geometrical and fluid-dynamic features. Thus, a specific research project is ongoing on the acoustic and thermal experimental characterization of selected multi-perforated liner geometries. In this paper, the complete experimental campaign on the acoustic behavior of the aforementioned liners has been carried out in the planar wave field range, that is of main concern in aero-engines. For this purpose, an innovative modular test rig has been designed to characterize test cases at ambient conditions, changing bias and main flows up to operating engine conditions. Liner geometries account for 3 different hole diameters, 5 different patterns and 2 hole inclinations, ranging within typical cooling system values; tests were performed with the two-source multi-microphone technique to evaluate global acoustic parameters independently from test rig boundary conditions. The acoustic performances of liners are discussed in terms of the energy dissipation coefficient.

Pumping Loss of Shrouded Meshed Spur Gears

2020 ◽  
Author(s):  
Michael J. Hurrell ◽  
Jerzy T. Sawicki
Keyword(s):  
High Speed ◽  
Fluid Dynamic ◽  
Spur Gear ◽  
Test Facility ◽  
Spur Gears ◽  
Cfd Analysis ◽  
Total Load ◽  
New Approach ◽  
Loss Component ◽  
Swept Volume

Abstract High speed rotorcraft transmissions are subject to load-independent power losses consisting of drag loss and pumping loss. Tightly conforming shrouds enclosing the transmission gears are often incorporated to reduce the drag component of the total load-independent losses. However, tightly conforming axial shrouds can result in an increase in the pumping loss component. Quantifying the pumping loss of shrouded gear transmissions has been the subject of many studies. This study presents a new approach for estimating pumping loss based on the concept of swept volume and examines the applicability of the approach to various shroud configurations. The drag loss and pumping loss of a shrouded spur gear pair has been determined through testing using the NASA Glenn Research Center (GRC) Gear Windage Test Facility. The results from this testing have been compared to theoretical results using the formulations presented in this study. In addition, computational fluid dynamic (CFD) analysis has been conducted for the various shroud configurations tested at NASA GRC. The results from the CFD analysis confirm the theoretical and empirical results and provide insight into the applicability of the swept volume approach for estimating pumping power loss of shrouded gear transmissions.

Analysis of the Oil Squeezing Power Losses of a Spur Gear Pair by Mean of CFD Simulations

2012 ◽  
Author(s):  
Franco Concli ◽  
Carlo Gorla
Keyword(s):  
High Efficiency ◽  
Fluid Dynamic ◽  
Axial Direction ◽  
Spur Gear ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Main Concern ◽  
Power Losses ◽  
Dynamic Simulations ◽  
Gear Mesh

Efficiency is becoming more and more a main concern in the design of power transmissions and the demand for high efficiency gearboxes is continuously increasing. Also the new restrictive euro standards for the reduction of pollutant emissions from light vehicles impose to improve the efficiency of the engines but also of the gear transmissions. For this reason the resources dedicated to this goal are continuously increasing. The first step to improve efficiency is to have appropriate models to compare different design solutions. Even if the efficiency of transmissions is quit high if compared to the efficiency of the engines and appropriate models to predict the power losses due to gear meshing, to bearings and to seals already exist, in order to have a further improvement, some aspects like the power losses related to the oil churning, oil squeezing and windage are still to be investigated. These losses rise from the interaction between the moving or rotating elements of the transmission and the lubricant. In previous papers [39, 40, 41 43, 44], the authors have investigated the churning losses of planetary speed reducers (in which there is a relative motion between the “planets + planet carrier” and the lubricant). This report is focused on the oil squeezing power losses. This kind of losses is associated with the pumping of the oil at the gear mesh, where there is a contraction of the volume between the mating gears due to the rotation of them and a consequent overpressure. This overpressure implies a fluid flow primarily in the axial direction and this, for viscous fluids, means additional power losses and a decrease of the efficiency. In this work this phenomena has been studied by means of some CFD (computational fluid dynamic) simulations with a VOF (volume of fluid) approach. The influence of some operating conditions like the rotational speed and the lubricant temperature have been studied. The results of this study have been included in a model to predict the efficiency of the whole transmission.

CFD Simulations of a Meshing Gear Pair

2016 ◽  
Author(s):  
E. Burberi ◽  
T. Fondelli ◽  
A. Andreini ◽  
B. Facchini ◽  
L. Cipolla
Keyword(s):  
Fluid Dynamic ◽  
Relative Magnitude ◽  
Gear Pair ◽  
Power Losses ◽  
Cfd Simulations ◽  
Pressure Fields ◽  
Torque Transmission ◽  
Many Sources ◽  
Different Sources ◽  
Numerical Approaches

Gearboxes are efficient systems for torque transmission, with an overall efficiency over 99 % if well designed. Nevertheless its use in high power applications lead to significant energy loss. Further improvement of efficiency can be reached analyzing in more detail the different sources of power losses within the transmission system. These losses can be classified into two groups, load-dependent and load-independent. Whereas the load-dependent power losses have been closely studied and predictive models have been already developed, on the contrary the fluid-dynamic losses require further analyses. There are many sources of such losses, but the primary ones are related to the windage, the oil squeezing due to the gear meshing and oil churning. The relative magnitude of these mechanisms varies depending on the application. The objective of this work is to study the meshing losses by means of CFD simulations. A gear pair has been analyzed, representing an experimental test available in literature. Transient RANS calculations have been performed, exploiting two different numerical approaches. The influence of the rotational speed on the fluid-dynamic resistant torque has been investigated, then the flow and pressure fields associated with the gears motion have been evaluated. The results are compared to experimental data in order to validate the most appropriate modelling.

Windage Losses of a Meshing Gear Pair Measured at Different Working Conditions

2018 ◽  
Author(s):  
D. Massini ◽  
T. Fondelli ◽  
B. Facchini ◽  
L. Tarchi ◽  
F. Leonardi
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Volume Flow Rate ◽  
Fluid Dynamic ◽  
Lubrication System ◽  
Test Rig ◽  
Rotating Speed ◽  
Aero Engine ◽  
Speed Up ◽  
Oil Jet

In recent years the aero-engine community is looking towards the reduction of specific fuel consumption by increasing the efficiency of gearing systems. Considering their weight contribution, internal power losses and lubrication requirements, they have indeed a direct impact on the engine overall efficiency. Even though nowadays gears have reached very high efficiencies, over 99%, all the power dissipated through losses is converted into heat that must be removed by the lubrication system. Heat reduction is hence beneficial for minimizing lubrication system dimensions that is crucial in aero engine applications where it is mandatory to limit the weight of every component. Among the sources of loss, two main categories may be distinguished: load dependent and load independent losses. The first ones are due to the transmission of torque and have been deeply studied in the last years, the latter are related to fluid-dynamic interaction between gears and the surrounding environment, they are negligible at low pitch line velocities, but become very important in high speed applications, typical of turbomachinery. This work deals with an experimental investigation of the load independent losses due to a couple of spur meshing gears working at different conditions in presence of an oil-jet lubrication system. The test rig allows the gears to rotate, at different velocities up to 15000 rpm, in a controlled environment contained in a sealed box. Test rig pressure can be imposed (0.3–1.0 bar) and monitored as well as the oil jet conditions, in terms of mass flow rate (jet volume flow rate up to 1.65 litres per minute), temperature (80–140 °C) and inclination angle. A high precision bearing-less torque meter, equipped with a speedometer, was exploited to measure at the same time the torque losses and rotating speed. Results of the experimental survey allowed a better understanding of load independent losses at pitch line speed up to 100 m/s and in different environmental conditions.

Windage and Churning Effects in Dipped Lubrication

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Anant S. Kolekar ◽  
Andrew V. Olver ◽  
Adam E. Sworski ◽  
Frances E. Lockwood
Keyword(s):  
Energy Loss ◽  
Spur Gear ◽  
Inertial Forces ◽  
Simple Test ◽  
Power Losses ◽  
Test Rig ◽  
Liquid Lubricant ◽  
Medium Speed ◽  
Significant Interest ◽  
Fluid Properties

In dipped (splash) lubrication, a rotating component, such as a gear, is partly submerged in a reservoir of liquid lubricant and acts to distribute it within the lubricated machine. Dipped lubrication is widely used for low to medium speed applications in the industrial and automotive sectors and there is a significant interest in the associated energy loss (the “churning” loss) because of its influence on efficiency and fuel consumption. In this study, a simple test rig consisting of a spur gear rotating in a cylindrical enclosure, partly filled with a liquid, was used to study the effect of fluid properties on the churning loss. The inertia rundown method was used to determine the power losses. Lubricating oils, water and aqueous glycerol solutions were among the fluids used. Correlations with Froude and Reynolds and Bond numbers are presented. It was found that the churning losses were significantly affected by the fluid disposition within the housing. In turn this was affected by the ratio of inertial forces to gravity (Froude number) and by air pressure. The influence of the pressure of the air within the enclosure was also investigated. When the air was evacuated from the enclosure, the churning losses increased, by a factor of up to 4.5 times. This can be explained by the effect of air (windage and aeration) on the liquid disposition, factors neglected in most previous work.

Computational and Experimental Study of Hot Streak Transport Within the First Stage of a Gas Turbine

2019 ◽  
Author(s):  
Paolo Gaetani ◽  
Giacomo Persico ◽  
Lorenzo Pinelli ◽  
Michele Marconcini ◽  
Roberto Pacciani
Keyword(s):  
Gas Turbine ◽  
High Speed ◽  
Fluid Dynamic ◽  
Spatial Coherence ◽  
Inlet Temperature ◽  
Turbine Stage ◽  
Complex Flow ◽  
Cfd Simulations ◽  
Azimuthal Position ◽  
Aero Engines

Abstract The paper discusses the migration, the interaction with the blades, and the attenuation of hot streaks generated by combustor burners, during their propagation within the first turbine stage of aero-engines. Experiments and Computational Fluid Dynamic (CFD) simulations were carried out in the framework of the European Project RECORD and on its follow-up. Measurements considering burner-representative temperature perturbations injected upstream of an un-cooled high-pressure gas turbine stage were performed in the high-speed closed-loop test-rig of the Politecnico di Milano (Italy). The hot streaks were injected in streamwise direction at the stage inlet in four different circumferential positions with respect to the stator blade. They feature a 20% over-temperature with respect to the main flow. Detailed temperature measurements as well as unsteady aerodynamic measurements upstream and downstream of the blade rows were performed. Time-accurate CFD simulations of the flow upstream and within the turbine stage were performed with the TRAF code, developed by the University of Florence. Measurements show a relevant attenuation of hot streaks throughout their transport within the stator and the rotor blade rows, highly depending on the injection azimuthal position. The perturbations were observed to lose their spatial coherence, especially in the transport within the rotor, and to undergo severe spanwise migration. Simulations exhibit a good agreement with the experiments on the measurement planes and allow tracking the complex flow phenomena occurring within the blade rows. Finally the aerodynamic and thermal implications of the inlet temperature perturbations are properly highlighted and discussed.

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