Engineer simulates airflow around backrider shield, shows it offers no protection

An engineer simulated the air flow around a backrider shield in a computer model

Just recently, the country’s biggest organization of mechanical engineers, Philippine Society of Mechanical Engineers, Inc. (PSMEI), has denounced the government’s new barrier requirement for backriding on motorcycles.

_{CFD simulation of airflow around a backrider shield with a rider in front.}

Inspired by the PSMEI’s position against the backride shield, an engineer built a 3D model of the backrider shield and simulated how air would flow around it while in motion. This simulation, called computational fluid dynamics (CFD), is intended to visualize how air particles travel around the riders and backrider shield. It is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid or air flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid — or in this case, air — and its interaction with surfaces defined by boundary conditions. This is the same method that car and motorcycle manufacturers, race teams, and aircraft engineers use to test their designs before building a prototype. 

Engineer Paul De Leon, shared that it only took him about an hour and a half (his lunch break) to create the rough design, import geometric models, run flow and mesh generation (Coarse Grid), boundary conditions, run-time, and flow visualization.

After modeling the barrier based on the rough dimensions approved by the IATF, Engr. Paul De Leon, ran two sets of tests for airflow: one with a rider and one without a rider, both running at approximately 30 kilometers per hour. The post was shared by PSME here.

As can be seen from the visualizations, the backrider shield creates vortices behind it. These vortices (little tornadoes caused by turbulence) can suck the air it's supposed to blow away back in. This exposes the backrider to even more air (and virus carrying-droplets suspended in them). Though initially designed to shield the backrider from the transmission of air droplets, it appears to have the opposite effect and may even draw air in.

After the simulation test, he concluded that, “All in all, I think the position paper is accurate and on point. The barrier [backride shield] has no benefit protection-wise due to air stagnation on the passenger side, [is] costly and increases the risk of accident .... as we probably have intuited beforehand.”

_{CFD simulation of airflow around a backrider shield without rider.}

Government stance

On Saturday, DILG spokesperson, Jonathan Malaya has maintained that their approved backride shield design is safe, and blames faulty installation by the rider as the reason for the mishaps. This echoes an earlier statement by the JTF COVID Shield commander, Lt. Gen. Guillermo Eleazar.

Malaya also added, in a separate interview, that the government is still considering other shield designs and has urged those interested to submit their ideas before its full implementation on July 31^st.