ISO 4391:1984 gives the common efficiency definition for positive displacement machines. ISO 4409:2019 uses this efficiency definition to specify the procedure for efficiency measurements. If the machine conditions do not correspond with an incompressible flow due to operation at high pressure levels, the compressibility of the fluid and the dead volume of a pump must be taken into account. On this point, ISO 4391:1984 is physically inconsistent. Achten et. al. address this issue in their paper at FPMC 2019 presenting a critical review of ISO 4409:2007. They introduce new definitions of the overall efficiency as well as the mechanical-hydraulic efficiency. At the same time, they question the validity of the volumetric efficiency definition. Li and Barkei continue on this issue in their paper at FPMC 2020 and give a new efficiency definition based on the introduction of a new quantity Φ which describes the volume specific enthalpy of the conveyed fluid. The motivation of this paper is to contribute to the ongoing and fruitful discussion. Our approach starts with the most general efficiency definition, namely the isentropic efficiency. Subsequently, we make assumptions concerning the fluid properties with respect to the compressibility of the conveyed fluid. On the basis of the ideal cycle of a positive displacement pump and the p-v diagram, we derive physically consistent and more meaningful representations of the overall, the mechanical-hydraulic and the volumetric efficiency that address the inconsistency of ISO 4391:1984. Furthermore, we compare our findings with the existing results of Achten et. al. and Li and Barkei.

When a fluid enters a rotating circular pipe a swirl boundary layer with thickness of δ̃ s appears at the wall and interacts with the axial momentum boundary layer with thickness of δ̃. We investigate a turbulent flow applying Laser-Doppler-Anemometry to measure the circumferential velocity profile at the inlet of the rotating pipe. The measured swirl boundary layer thickness follows a power law taking Reynolds number and flow number into account. A combination of high Reynolds number, high flow number and axial position causes a transition of the swirl boundary layer development in the turbulent regime. At this combination, the swirl boundary layer thickness as well as the turbulence intensity increase and the latter yields a self-similarity. The circumferential velocity profile changes to a new presented self-similarity as well. We define the transition inlet length, where the transition appears and a stability map for the two regimes is given for the case of a fully developed axial turbulent flow enters the rotating pipe.

This paper investigates analytically the advantage of the embedded propulsion compared to a state of the art propulsion of an aircraft. Hereby, we are applying the integral method of boundary layer theory and potential theory to analyse the boundary layer thickness and the impact of the flow acceleration due to the embedded propulsion. The aircraft body is treated as a flat plate. The engine is treated as a momentum disc but there is a trade off, since the engine efficiency is effected by the boundary layer. The outcome of the energetic assessment is the following: the propulsion efficiency is increased by the embedded propulsion and the drag of the aircraft body is reduced. The optimized aircraft engine size depending on Reynolds number is given.

Acceptance tests on large fans to prove the performance (efficiency and total pressure rise) to the customer are expensive and sometimes even impossible to perform. Hence there is a need for the manufacturer to reliably predict the performance of fans from measurements on down-scaled test fans. The commonly used scale-up formulas give satisfactorily results only near the design point, where inertia losses are small in comparison to frictional losses. At part- and overload the inertia losses are dominant and the scale-up formulas used so far fail. In 2013 Pelz and Stonjek introduced a new scaling method which fullfills the demands ( [1], [2]). This method considers the influence of surface roughness and geometric variations on the performance. It consists basically of two steps: Initially, the efficiency is scaled. Efficiency scaling is derived analytically from the definition of the total efficiency. With the total derivative it can be shown that the change of friction coefficient is inversely proportional to the change of efficiency of a fan. The second step is shifting the performance characteristic to a higher value of flow coefficient. It is the task of this work to improve the scaling method which was previously introduced by Pelz and Stonjek by treating the rotor/impeller and volute/stator separately. The validation of the improved scale-up method is performed with test data from two axial fans with a diameter of 1000 mm/250mm and three centrifugal fans with 2240mm/896mm/224mm diameter. The predicted performance characteristics show a good agreement to test data.

The influence of Reynolds number, roughness and turbulence on the onset of wall stall is up to now not sufficiently understood. To shed some light onto the interdependency of near wall flow with growing swirl component, the simplest “machine” is tested. The apparatus we examine is a circular pipe at rest followed by a rotating co-axial pipe segment. In the sense of a generic experiment this machine represents a very basic model of the inlet of an axial machine. Due to the wall shear stress a swirl boundary layer is formed in the rotating pipe segment, interacting with the axial boundary layer. The evolution of the swirl velocity profile with increasing axial distance from the rotating pipe inlet is measured for various Reynolds numbers, flow numbers and degrees of turbulence by means of Laser Doppler Anemometry. We observe a self-similarity in the swirl velocity profile, for subcritical flow number and develop a scaling law for the velocity distribution in the transition section of a rotating pipe. At critical flow number the boundary layer is separating, resulting in a ring vortex at the inlet of the rotating pipe. Our work fills the gap of previous experimental works, with respect to high Reynolds numbers and low flow numbers. The parameter field we examine is most relevant for turbomachinery application and wall stall. In addition our boundary layer resolution is sufficient to resolve the swirl boundary layer thickness. Only this high resolution enables us to generalize the experimental findings by means of a similarity distribution of the velocity profile within the swirl boundary layer.

Specific turbocharger parameters are necessary to develop and match model based control strategies in the air path of a turbocharged engine. These parameters describe the turbocharger performance and are obtained from measurements on manufacturers’ standard test benches under steady state conditions and without taking into account the heat transfer between the components of the turbocharger or between the turbocharger and the surroundings. The latter falsifies the measured turbocharger efficiency which can be referred as “apparent efficiency”. The efficiency is a key parameter of the model based controls. Thus, the apparent efficiency increases the uncertainties (mismatching) and slows down the matching process considerably. Due to the mismatching, manufacturers’ parameters themselves need to be calibrated. The calibration occurs on the basis of on-board measurements and offline analyses. However, this calibration procedure is not axiomatic and the results remain typical for a certain turbocharger and engine combination. Hence, it is usually not possible to apply the results when the same turbocharger should be matched with another engine. A physically based scaling method has already been introduced in previous publications in order to obtain the “real” from the “apparent” efficiency, [1]. This work aims to show on the basis of a concrete example how the implementation of this method counteracts the mismatching without any further measurements. As a result, the matching process can be accelerated and enhanced. The reusability of the results leads to faster processes and lower costs.

In calibration tasks under engine conditions, steady-state manufacturer performance maps are applied to periodic turbocharger operation. This procedure is exposed to considerable uncertainties. In this work the axiomatic form of the energy equation as well as Euler turbomachinery equation are used to generate a general form of the respective equations which allow for periodicity. Thus, the concept of apparent speed and apparent efficiency is introduced. The latter can attain values greater than unity.

Losses through secondary flows occur in every turbomachine. Between the rotating blades and the casing of a turbomachine there is a secondary flow through the tip clearance caused by the pressure difference between the pressure and the suction side of the blade. This tip leakage flow is not involved in the work done by the rotating blades hence it reduces the aerodynamic efficiency. The flow through the tip clearance rolls up to a spiral vortex on the suction side of the blade and induces drag. Size and circulation of this vortex, according to the Helmholtz vortex theorem, depend on the bound vortex and the width of the tip clearance. Examinations of this structure lead to an idea of describing the tip vortex loss with analytical methods. Therefore an analytical approach is made regarding mainly the circulation at the blade tips. The method is discussed critically in the context of known loss models. It is shown to be a good summary of earlier methods. Since no explicit geometry data of the turbomachine is needed, it is much easier to use. The most important aspect is the excellent agreement with measurements performed at the Chair of Fluid Systems Technology. In total eleven different fan configurations are measured and analyzed in regard to their tip clearance losses. The measurements are performed at a test rig located at the laboratory of the Chair of Fluid Systems Technology at Technische Universität Darmstadt. Additionally further published measurement data is used to validate the method.

In addition to the objective of increasing the efficiency of fans, acoustic efficiency gains more and more importance in order to reduce fan noise exposure. Whereas previously, research in this field was focused basically on blade design, nowadays the peripheral devices of fans are more often the object of study, since technical understanding of noise development is comparatively incomplete. Therefore, fundamental studies are essential to gain insight in the patterns of noise development and relatively easy opportunities to reduce noise level. In order to combine good aerodynamic properties with a silent fan, this experimental research investigates the acoustic and aerodynamic characteristics of an axial turbomachine and possibilities of reducing the emitted sound. Therefore a sound absorber ring is built directly around the rotor of a fan in order to absorb the sound very close to the origin. The fan assembly is installed in a test rig according to ISO 5136, which defines a standard for determining sound power radiated into a duct by fans. Acoustic signals are recorded with two microphones in the test duct, one on the pressure side, the second on the suction side, each close to anechoic terminations at the ends. The aerodynamic characteristics are determined with a calibrated inlet nozzle and static pressure measurements over the fan stage. To confirm the expectation that a significant part of the emitted sound power is tip clearance noise, which changes with the operating point, the volume flow of the fan is varied over its entire operating range. In this study, five different porous materials are tested for their ability of deadening the sound of the fan. In order to measure the influence of the construction which contains the materials, the perforated casing ring with a sound-reflecting termination and a plane ring with the same tip clearance are measured additionally as a reference. The noise exposure is analyzed over the complete frequency spectrum in order to determine the absorbing frequencies of the materials.

In addition to developing fans as aerodynamically efficient as possible, acoustic optimization gains more and more importance for the purpose of reducing fan noise exposure. In order to combine good aerodynamic properties with a silent fan, this experimental research investigates the acoustic and aerodynamic characteristics of an axial fan. In this case, a fan with skewed blades is tested in view of its aerodynamic efficiency and noise exposure in dependence on its tip clearance and stagger angle. For this purpose, six different stagger angles and five tip clearance gaps per angle were measured in a fan test rig (according to ISO 5136). Interpretation of the recorded data shows a clear trend toward higher aerodynamic efficiency and less noise with a down-sizing of the tip clearance gap. As the cost of manufacture rises with the decrease of the tip clearance, the efficiency of these measures can be calculated with the results of this study under consideration of aerodynamic and acoustic aspects.

There is a need to reliably predict the performance (efficiency and total pressure rise) of axial turbomachines from model tests for different load ranges. The commonly used scale-up formulas are not able to reliably predict the performance, especially beyond the design point. Furthermore these formulas do not regard changes in relative roughness as they usually occur in practice. An improved scale-up formula is proposed which achieves not only the reliable scale-up of efficiency, but also the scale-up of the pressure coefficient. It is motivated from measurements on two geometric similar axial model fans with a diameter of 1000 mm respectively 250 mm at different rotational speeds, hence Reynolds numbers. By bonding grains of sand to the impeller the influence of relative roughness was investigated. For applying the formula to different load ranges a factor V is introduced that depends on the quotient of effective flow coefficient to optimal flow coefficient.