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Performance and flow dynamics of heavy air curtains using experiments and numerical simulations

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Abstract

Air curtain devices (ACD) are commonly installed in domestic and commercial buildings to suppress the buoyancy-driven exchange flow through a doorway opening. Generally, the operating density of an ACD is equal to that of the indoor space making it neutrally buoyant. In the present study, we evaluate the performance of heavy air curtains where the operating density of the ACD is higher than that of the ambient fluid. The primary objective is to quantify the air curtain effectiveness, E, that determines the thermal comfort of building occupants based on the mean temperature inside the interrogated region. Experiments and numerical simulations are conducted and validated for various values of deflection modulus, \(D_m\), that compare the relative magnitude of the jet momentum and transverse stack effect due to buoyancy. The other important non-dimensional parameter is the density ratio, S, which compares the extent of added buoyancy in ACD to that of across the doorway. In addition, the velocity dynamics of the air curtains are compared with an isothermal jet to understand the underlying effects that the buoyancy causes on the jet development. The general structure of air curtains that characterize the jet inclination and penetration is visualized through injecting a dye, and it agrees very well with the buoyancy distribution obtained using simulations at different \(D_m\). Upon introduction of an assisting buoyancy, it has been found that the infiltration reduces by 25% compared to a neutrally buoyant air curtain for practical values of \(D_m\).

Article Highlights

  • Heavier air curtains are more effective as compared to the neutrally buoyant air curtains.

  • The deceleration of mean centreline velocity is more prominent at smaller deflection modulus.

  • Stability may be achieved at slightly smaller deflection modulus for heavier air curtains.

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Acknowledgements

We sincerely thank the technical staff of the fluid mechanics laboratory and Mr. Ayank Raj for their invaluable assistance during the experiments. The insightful discussions with Dr. Ed Santilli from Thomas Jefferson University on setting up the LES simulations using SOMAR are highly appreciated and greatly enhanced the quality of our research. We also appreciate the constructive feedback of anonymous reviewers and Prof. Sridhar Balasubramanian for his editorial handling of the manuscript.

Funding

Tanmay Agrawal acknowledges the Prime Minister Research Fellowship (PMRF) provided by the Government of India, while Narsing Kumar Jha acknowledges the seed grant (PLN12/04AM) and matching grant (MI02572G) supports from Indian Institute of Technology Delhi.

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Authors and Affiliations

  1. Department of Applied Mechanics, Indian Institute of Technology Delhi, Hauz Khas, Delhi, 110016, India

    Tanmay Agrawal, Shresth Agarwal, Vamsi Krishna Chalamalla & Narsing Kumar Jha

Authors
  1. Tanmay Agrawal
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  2. Shresth Agarwal
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  3. Vamsi Krishna Chalamalla
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  4. Narsing Kumar Jha
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Contributions

Experiments were conducted jointly by TA and SA under the mentorship of NKJ. The numerical simulations and the corresponding data analysis was done by TA under the supervision of VKC. The first draft of the manuscript was written by TA and SA and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Narsing Kumar Jha.

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Appendix A Numerical validation

Appendix A Numerical validation

Towards the validation of the employed numerical solvers, the case of a plane turbulent jet was simulated at a Reynolds number of 5000 and compared with the existing literature. In Fig. 9a, we compare the normalized mean vertical velocity, \(\tilde{w} = \frac{\overline{w}_{CL}}{w_0}\), along the jet centerline with the analytical solution [42] and the experimental data of Khayrullina et al. [4]. A very good agreement can be observed in the self-similar region for the LES computations whereas the decay rate, \(d \tilde{w}/dz\), is predicted well using both RANS and LES. This indicates the suitability of the adopted meshes and the numerical methods.

Fig. 9
figure 9

Validation of the numerical results for a plane jet at \(Re =\) 5000

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Whereas in Fig. 9b, we validate the normalized velocity profile in the self-similar region, \(w^* = \frac{\overline{w}}{\overline{w}_{CL}}\), in the transverse direction x. The hotwire data of Gutmark and Wygnanski [5] is also included for this comparison. The Gaussian velocity distribution, which is characteristic of that of planar jets, is exhibited by all the numerical simulations. In the inset of this figure, the velocity distribution near the nozzle exit is plotted to illustrate the near top-hat profile supplied as the boundary condition. A detailed discussion on this validation is presented in [29].

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Agrawal, T., Agarwal, S., Chalamalla, V.K. et al. Performance and flow dynamics of heavy air curtains using experiments and numerical simulations. Environ Fluid Mech (2023). https://doi.org/10.1007/s10652-023-09948-8

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