###### Abstract  
Precise prediction of ventilation flow is essential to create a comfortable, economical, and healthy indoor environment. In the past three decades, the computational fluid dynamics (CFD) method has been used more often, and it is now one of the primary methods for studying building ventilation. The most common CFD method is RANS simulation because of the low cost of computational resources and good accuracy. This paper presents a numerical investigation of a transitional ventilation flow with the Coanda effect, which makes the initial free jet transform into a wall jet. Six low-Reynolds number \(k\)-\(\varepsilon\) models proposed by [PERSON] (AB), [PERSON] (LB), [PERSON] (LS), [PERSON] (YS), [PERSON] and [PERSON] (AKN), and [PERSON], [PERSON] and [PERSON] (CHC) are applied. The performance of the six models is evaluated by comparing the computational results with the PIV measurements of [PERSON] et al. The predictions revealed that the LS model has a good approximation of velocity profiles because of its two extra terms in \(k\) and \(\varepsilon\) equations, and the AB model is in good agreement with experimental results for predicting the Coanda effect. The LB model provides the worst agreement with experimental data on account of the wrong prediction of turbulent kinetic energy and dissipation rate. low-Reynolds number \(k\)-\(\varepsilon\) model; transitional flow; CFD simulations; Coanda effect; building ventilation +
Footnote †: journal: Applied Sciences  
the streamline pattern, and the velocity profile has been measured by an anemometer. He has reported that a steady two-dimensional flow will arise when the length of the model is less than 3-4 times its height, and if the length of the model gets much longer, a very unsteady flow may take place. He has predicted the ventilation performance by the \(k\)-\(\varepsilon\) model. He has further investigated the differences between the experimental and predicted results and found that the prediction results are highly consistent with the experimental data. After [PERSON]'s research, more and more studies on building ventilation have been proposed. Nevertheless, most of these studies were conducted at fully turbulent Reynolds numbers and did not take into account the Coanda effect, a widespread phenomenon in building ventilation. [PERSON] et al. (2017) have studied the transitional ventilation flow injected from the upper left corner and discharged from the lower right corner in a slot-ventilated enclosure with the inlet Reynolds numbers between 1000 and 2500. They have used two PIV systems to measure velocity and a flow visualization system to observe the jet region and large vortical structures below the jet region. They have reported that the turbulence intensities are higher in the shear layer. Below the shear layer, the turbulence intensities are Re-independent. They have also mentioned that with the increasing of Reynolds numbers, the position of maximum jet velocity in the y direction increases, the same as the size of the recirculation region in the central area. They have paid close attention to the Coanda effect. The Coanda effect makes the initial free jet (injected not against the ceiling) transform into a wall jet. This phenomenon ensures that the fresh air will not enter the living area too early and can help not make the room's residents feel uncomfortable. The Coanda effect can be caused by the lower pressure generated by the jet entrainment of surrounding fluid between the wall and the free jet. The experiment done by [PERSON] et al. (2017) is numerically investigated by [PERSON] et al. (2018). They have used the low-Reynolds number \(k\)-\(\varepsilon\) model of [PERSON] et al. (2018) and the SST \(k\)-\(\omega\) model ([PERSON] et al., 2018). They have studied the influence of inlet boundary conditions on predicting ventilation performance by applying a series of different turbulence intensities and turbulent length scales at Re = 1500.