Active Drag Reduction of Ground Vehicles Using Air-Jet Wheel Deflectors

Seven turbulence models were used to simulate the flow within the wheelhouse of a simplified vehicle body. The performance of each model was evaluated by comparing the aerodynamic coefficients obtained using computational fluid dynamics (CFD) to data collected from wind tunnel experiments. The performance of large eddy simulation (LES) and detached eddy simulation (DES) was largely dependent on the time step and grid size to accurately resolve turbulent eddies. The standard k-e, realizable k-e, k-w, DES, and LES all trended towards a drag coefficient which was 20% lower than the experimental value. In all numerical cases, the lift coefficient was found to be at least 60% greater than the experimental value, but was consistent with numerical studies by other authors. The standard k-w and SST k-w models provided results which were the most consistent with experimental data for the three different mesh sizes. Two types of flow modification devices were then added to the simplified vehicle model to assess drag reduction potential. Conventional wheel defectors are compared to air-jet wheel defectors on wheel drag and overall drag reduction capabilities. Two parametric studies are conducted on the Fabijanic body at a Reynolds number of 1.6x105: a study on the variation of the size and location of a conventional wheel defector, and a study on the jet speed and location of an air-jet wheel defector. Results show that wheel drag is decreased as the height of the conventional wheel defector is increased, and that the further the conventional wheel defector is from the wheelhouse, the more sensitive the wheel is to changes in drag coefficient. The air-jet wheel defector successfully decreases the wheel drag. The closer the air-jet is to the wheelhouse the less of an impact it has on wheel drag, but the greater the impact on the overall drag of the simplified body. A maximum overall drag reduction of 2.76% is achieved with a configuration which also results in a wheel drag reduction of 16%. Air-jet wheel defectors were then simulated on the DrivAer reference model -- an open source model which blends features of the Audi A4 and the BMW 3 Series. The air jets were found to be less impactful at low speeds, but at higher speeds, they were observed to reduce wheel drag and cause an overall drag reduction of up to 5.1%. Even though jet speeds as high as twice the driving speed were investigated, and caused relatively large reductions in wheel drag, a jet speed approximately 2/3 of the driving speed was observed to cause the greatest overall reduction

Assessment of Conventional and Air-Jet Wheel Deflectors for Drag Reduction of The DrivAer Model

Aerodynamic drag is a large resistance force to vehicle motion, particularly at highway speeds. Conventional wheel deflectors were designed to reduce the wheel drag and, consequently, the overall vehicle drag; however, they may actually be detrimental to vehicle aerodynamics in modern designs. In the present study, computational fluid dynamics simulations were conducted on the notchback DrivAer model—a simplified, yet realistic, open-source vehicle model that incorporates features of a modern passenger vehicle. Conventional and air-jet wheel deflectors upstream of the front wheels were introduced to assess the effect of underbody-flow deflection on the vehicle drag. Conventional wheel-deflector designs with varying heights were observed and compared to 45◦ and 90◦ air-jet wheel deflectors. The conventional wheel deflectors reduced wheel drag but resulted in an overall drag increase of up to 10%. For the cases studied, the 90◦ air jet did not reduce the overall drag compared to the baseline case; the 45◦ air jet presented drag benefits of up to 1.5% at 35 m/s and above. Compared to conventional wheel deflectors, air-jet wheel deflectors have the potential to reduce vehicle drag to a greater extent and present the benefit of being turned off at lower speeds when flow deflection is undesirable, thus improving efficiency and reducing emissions

Engineering Graphics Concept Inventory: Instrument Development and Item Selection

[EN] More reliable instruments need to be developed to assess curricula and measure student learning. It is important to ensure that students properly understand fundamental concepts, as scaffolding learning on a poor foundation can have a negative cascading effect. A concept inventory is an example of an instrument that aims to assess student learning and identifying their misconceptions. Such an instrument is typically comprised of an assessment whose items are prudently chosen to test understanding of a single concept per item. The result of this careful selection of items for the Engineering Graphics Concept Inventory resulted in a 30-question multiple choice instrument that can be used to identify deep-seated misconceptions and to assess course outcomes. This paper will outline the development of the Engineering Graphics Concept Inventory, focusing specifically on developing distractors and the selection process for the items in the instrument. The instrument will provide a means to assess and streamline curricula for engineering graphics educators. The research team would like acknowledge the support of NSF grants 1432280 and 1432288.http://ocs.editorial.upv.es/index.php/HEAD/HEAD18Nabutola, K.; Steinhauer, H.; Nozaki, S.; Study, N.; Sadowski, M. (2018). Engineering Graphics Concept Inventory: Instrument Development and Item Selection. Editorial Universitat Politècnica de València. 1317-1324. https://doi.org/10.4995/HEAD18.2018.8196OCS1317132

Workshop 7: Assessing Pre-Existing Student Knowledge: How to Identify Foundational Misconceptions

All students bring to the classroom pre-existing knowledge. This prior knowledge can often be deeply held misconceptions. These misconceptions can be based upon incorrect understanding, teacher induced confusion, or common sense . These misconceptions can be deeply held and interfere with students learning key new concepts. In this workshop, we will provide participants with the opportunity participate in the process of identifying foundational concepts, ranking these foundational concepts (in reference to difficulty and importance), creating conceptual questions, and generating the appropriate distractors. All participants will also be provided with an overview into the structure and purpose of a Delphi panel on the identification and ranking of key concepts. Participants will also be provided statistical overview as to identify the most impactful questions. Through an NSF supported grant the authors have generated a concept inventory (a criterion referenced assessment) for engineering graphics and will use their research process/experience as a framework. Our goal is that all attendees leave the workshop with better understanding of the impact of student prior knowledge-in particular incorrect knowledge and how to identify and correct them in their own courses

Estimation of infection risk through airborne transmission in large open spaces with different air distributions

Respiratory diseases such as COVID-19 can be spread through airborne transmission, which is highly dependent on the airflow pattern of the studied room. Indoor air is typically not perfectly mixed even using a mixing ventilation, especially in large spaces. Airflow patterns in large open spaces such as hotel banquet rooms and open plan offices, are of particular concern, as these spaces usually accommodate more occupants and thus have the potential to spread diseases more rapidly leading to outbreaks. Therefore, understanding airflow patterns in large open spaces can help to estimate the detailed infection risk at certain locations in the space, which can prevent the spread of virus and track the potential new infections. This study estimated airflow patterns in a typical banquet room under theatre and banquet scenarios, and a large open plan office using computational fluid dynamics (CFD) simulations. Typical ventilation and air distribution approaches, as well as room layouts and occupant configurations in these scenarios were studied and applied in simulations. According to current results, the air distribution in a typical hotel banquet room with mixing ventilation can be very complicated, particularly for the banquet scenario. For a typical theatre scenario, under typical ventilation design, people sitting in the middle and lateral area were exposed to the highest infection risk. The front rows may be exposed to short-range transmission as well. For a banquet scenario, people sitting on the same table were more likely to be cross contaminated. But cross-table infection was still possible. The results can provide guidance on designing ventilation and air distribution approaches in large spaces with similar settings