Online (Remote) Teaching for Laboratory Based Courses Using “digital Twins” of the Experiments

Covid-19 pandemic has introduced radical changes to the engineering education so that most of the teaching moved to the off-campus setting of online classes. However, conducting the laboratory classes, a fundamental part of engineering education has remained to be a challenge. To address to this situation, an ambitious approach is taken to re-establish the laboratory experience entirely online with the help of digital twins of the laboratory experiments. Laboratory based undergraduate courses are important parts of the curriculum at the Lucerne University of Applied Sciences (HSLU), Switzerland. During the Covid-19 pandemic, it was necessary to adapt to the new environment of remote learning and modify the laboratory experiments so that they can be carried out online. The approach was to develop digital twins of each laboratory experiment with web applications and to provide an environment together with supporting videos and interactive problems so that the laboratory experiments can be carried out remotely. This paper explains the development of the digital twins of the laboratory experiments and provides information about the selected experiments such as potential vortex, linear momentum equation, diffuser flow, radial compressor, fuel cell, and pump test rig. A remote or distance learning has many hurdles, a major one being how to teach hands-on laboratory courses outside of an actual laboratory. The experience at the HSLU showed that teaching online laboratories using the digital twins of the experiments can work and the students can take part in remote laboratories that meet the learning objectives.

Study of the Effect of Vertical Airfoil Endplates on Diffusers in Vehicle Aerodynamics

Diffusers and the floor ahead of them create the majority of the downforce a vehicle creates. Outside motorsports, the diffuser is relatively unused, although its interaction with the ground is a consistent field of study owing to the aerodynamic benefits. The diffuser flow behavior is governed by three fluid-mechanical mechanisms: ground interaction, underbody upsweep, and diffuser upsweep. In addition, four different flow regimes appear when varying ride height, the vortices of which have great importance on downforce generation. The present study focuses on the diffuser’s fluid-dynamic characteristics undertaken within an academic framework with the objective of finding and understanding a high level of performance in these elements. Once the functioning of diffusers has been analyzed and understood, a new configuration is proposed: rear vertical airfoil endplates. The aim of the paper is to study the effect in performance of vertical airfoil endplates on diffusers in vehicle aerodynamics in a simplified geometry. The candidate to this geometry is the inversed Ahmed body, a geometry that is used as a model that simulates the flow behavior of car diffusers. Three different diffuser configurations are performed, namely 0° diffuser, 25° diffuser, and in the third case vertically installed rear vertical airfoil endplates are added to the 25° diffuser Ahmed body to change the flow field. These analyses are carried out by using open-source CFD simulation software OpenFOAM. An inlet velocity of 20 m/s is considered, as this is a typical velocity when cornering in motorsport. It is concluded that the 25° diffuser configuration generated more downforce than the 0° diffuser, which makes sense as the aim of adding a diffuser is to increase the amount of downforce produced. In addition, and as a result of the newly proposed configuration, the 25° diffuser Ahmed body with the vertical airfoil endplates emerges in a substantial increase of downforce thanks to the low-pressure zone generated at the back of the body.

Effect of vaned diffuser clocking position on hydraulic performance and pressure pulsation of centrifugal pump

The clocking position of the vaned diffuser, the circumferential position of the vaned diffuser relative to the volute, has a certain effect on the performance of the centrifugal pump. Therefore, this paper studies the guide vane centrifugal pump from the aspects of pressure pulsation, hydraulic performance, and energy loss. The maximum difference in efficiency is 3.4% under the design flow rate, and the maximum difference in the head coefficient is 4.7%. The hydraulic performance and pressure pulsation present different trends with the increase of the vaned diffuser clock angle. When the hydraulic performance and pressure pulsation are relatively good, the circumferential distance between the tongue and the upstream vaned diffuser blade is 3/4 of the diffuser flow path. In addition, the recommended vaned diffuser installation location may also be suitable for centrifugal pumps of similar construction. The energy loss was visualized using the theory of entropy production. The distributions of energy loss and flow field indicate that the energy loss of impeller and vaned diffuser changes little. The change of the vortex in the tongue and outlet area will cause a significant change in the energy loss of the volute, which is the main reason that the hydraulic performance of the centrifugal pump is affected by the clocking position of the vaned diffuser.

Boundary Layer Flashback Model for Hydrogen Flames in Confined Geometries Including the Effect of Adverse Pressure Gradient

The combustion properties of hydrogen make premixed hydrogen-air flames very prone to boundary layer flashback. This paper describes the improvement and extension of a boundary layer flashback model from Hoferichter [1] for flames confined in burner ducts. The original model did not perform well at higher preheat temperatures and overpredicted the backpressure of the flame at flashback by 4–5x. By simplifying the Lewis number dependent flame speed computation and by applying a generalized version of Stratford’s flow separation criterion [2], the prediction accuracy is improved significantly. The effect of adverse pressure gradient flow on the flashback limits in 2° and 4° diffusers is also captured adequately by coupling the model to flow simulations and taking into account the increased flow separation tendency in diffuser flow. Future research will focus on further experimental validation and direct numerical simulations to gain better insight into the role of the quenching distance and turbulence statistics.

Large-Eddy Simulation of an Asymmetric Plane Diffuser: Comparison of Different Subgrid Scale Models

Large-eddy simulation (LES) of separated turbulent flow through an asymmetric plane diffuser is investigated. The outcome of an actual LES depends on the quality of the subgrid-scale (SGS) model, as well as the accuracy of the numerical method used to solve the equations for the resolved scales. In this paper, we focus on the influence of SGS models for LES of the diffuser flow through using a high-order finite difference method to solve the equations for the resolved scales. Six resolutions are computed to investigate the influence of mesh resolution. Four existing SGS models, a new one-equation dynamic SGS model and a direct numerical simulation (DNS) are conducted in the diffuser flow. A series of computational analyses is performed to assess the performance of different SGS models on the coarse grids. By comparison with the experiment and DNS, the results produced by the new one-equation dynamic model give better agreement with experiment and DNS than the four other existing SGS models.

LDV Characterization of Unsteady Vaned Diffuser Flow in a Centrifugal Compressor

Modern turbomachinery faces increased performance demands in terms of efficiency, compactness, and pressure-rise. Advancements in computational technology have allowed numerical methods to become the backbone of design development efforts. However, the unique complexities of centrifugal compressor flow-fields pose difficult computational problems. As such, advanced experimental methods must be used to obtain high-quality datasets to further inform, improve, and validate computational methods in complex flow regimes. Recent experimental work on a high-speed centrifugal compressor has provided detailed, unsteady, three-component velocity data using Laser Doppler Velocimetry. A passage vortex is present and its nascent tied to the increased incidence at mid-span associated with impeller wake flow. This vortex begins in the hub-pressure side corner and grows to fill the passage and become temporally stable. The vortex development is unsteady in nature and the unsteady effects persist 40% downstream of the throat. Distinct jet and wake flow patterns from the impeller also do not agglomerate until 40% downstream of the throat. Additionally, the critical impact of the unsteady flow development on the time-averaged flow-field is explained.