## 1 Introduction  
This work studies the flow configuration of a supersonic gas jet in a plenum pointed toward a wall with a converging outlet pipe opening aligned with the jet. This configuration is industrially relevant for pulse-gas filter regeneration systems that perform periodic backwash pulses to remove solid cake from the filtering media. In these systems, gas pulses lasting less than a second (50 to 1000 ms) are directed toward the filtering media in the reverse direction compared to the filtration process to enable backwash of the media. This regeneration [1] is performed without interrupting the main process flow, cleaning a subset of the total filtering media each time. Such an online regeneration capability allows the avoidance of periodic shutdowns and manual disassembly to clean the filters. The capability of regenerating the filters during operation is especially desirable in systems processing hazardous materials or in systems with a high loading rate of solid particulates in the gas. The optimization of pulse-jet system designs often relies on prototyping and testing. However, the adoption of computational fluid dynamics (CFDs) reduces the cost of individual steps in parametric exploration, thus allowing enhanced optimization at a reduced cost. The suitability of CFD for pulse-jet applications has been supported by numerous validation studies. The studies often tested two-dimensional or three-dimensional Reynolds-averaged Navier-Stokes (RANS) models against pressure measurements collected in pulse-jet system experiments [2; 3; 4]. The present work extends CFD validation to flow visualization and velocity measurements acquired inside the supersonic jet through a combination of shadowgraphy and velocimetry. To the best knowledge of the authors, this paper presents the first application of high-resolution measurements for a filter pulse-jet configuration. Flow velocity is measured with molecular tagging velocimetry (MTV). MTV is an optical time-of-flight technique that transforms fluid molecules into temporary tracers through resonance excitation by photons (of a set wavelength). While particle image velocimetry (PIV) requires the injection of solid particles acting as tracers, in MTV, the gas molecules themselves are converted into tracers; thus, the inertial effects on tracers are minimal, and shock waves are captured faithfully. MTV techniques (under different names) have been widely used to measure supersonic gas jets [5; 6; 7]; see [PERSON] and [PERSON] [8] for a recent detailed review. Similarly, CFD methods have been widely compared with high-resolution data in supersonic jets [9]. Prior CFD validations for pulse-jet configurations have focused mainly on systems with fabric filters, displaying challenges in accurately predicting pressure in the ramp-down period as the filter deforms [3]. This work focuses on solid-mesh filters. Fabric filters can be backwashed more easily than solid-mesh filters because pulse jets cause the fabric to inflate and reach its elastic limit, resulting in rapid deceleration and release of accumulated cake. However, fabric filters are not suitable for high-temperature (hot gas) filtration, for which rigid self-supporting media are necessary to ensure mechanical, chemical, and thermal stability [1]. Backwash of solid-mesh filters relies solely on the direct interaction between the fluid flow and the filter cake, which is established through design optimization. The performance of backpulse in solid filters has been extensively evaluated in the literature based on theoretical and experimental evaluations [10] and the evaluation of effects on the filter cake [11]. A key component of the backpulse system, whose role has been debated, is the pipe connecting the filter outlet flange to the downstream plenum (defined considering the direction of normal filtration). This pipe is present in systems with both fabric and solid-mesh filters and industrially referred to as a \"Venturi\" due to the commonly encountered converging-diverging cross-section.