Characteristics of microjet hydrogen diffusion flames stabilized near extinction are investigated numerically. Two-dimensional simulations are carried out using a detailed reaction mechanism. The effect of burner wall material, thickness, and thermal radiation on flame characteristics such as flame height and maximum flame temperature are studied. Results show that the flame stabilizes at lower fuel jet velocities for quartz burner than steel or aluminum. Higher flame temperatures are observed for low conductive burners, whereas the flame length increases with an increase in thermal conductivity of the burner. Even though thermal radiation has a minor effect on flame characteristics like flame temperature and flame height, it significantly influences the flame structure for low conductive burner materials. The burner tip and its vicinity are substantially heated for low conductive burners. The effect of burner wall thickness on flame height is significant, whereas it has a more negligible effect on maximum flame temperature. Variation in wall thickness also affects the distribution of H and HO₂ radicals in the flame region. Although the variation in wall thickness has the least effect on the overall flame shape and temperature distribution, the structure near the burner port differs.

This numerical study investigates steady separated flow past a grooved circular cylinder within the Reynolds number range $7.5\le R{e}_D\le 30$, comprising variations in groove depth ($h$) and spacing ($\beta$). The groove width ($w$) is kept constant, while h/w varies across four levels ($0.5\le h/w\le 2$) and $\beta$ across five angles ($10°\le \beta \le 45°$). The results exhibit strong agreement with unbounded flow data, confirming blockage independence across the examined regime. Detailed analysis shows that $\beta$ has a stronger influence than $h/w$ on surface-pressure-dependent variables ($C_{p,0}$, $C_{p,b}$, $C_D$, ${\theta }_{sep}$) and wake-defining parameters ($L_w$, $W_w$, $\xi$, $\eta$), underscoring the dominant role of $\beta$ in rectilinear groove aerodynamics. In this regard, a critical spacing of $\beta =20°$ is observed, beyond which the sensitivity of the parameters toward the cylinder configuration decreases. Thus, significant flow control and drag reduction are attained for $R{e}_D=7.5$ at the lowest spacing $\beta =10°$, regardless of the groove’s $h/w$. Among these, the streamwise-oriented variables, $C_{p,0}$, $C_D$, $L_w$, $\xi$, and $u_{min}$, exhibit monotonic trend with respect to $\beta$ and are modeled using power-law relations. The models for $C_{p,0}$ and $C_D$ exhibit significant accuracy with $R^2\approx 0.999$ across all $\beta$ values considered, while it is 0.89–0.98 for $L_w$, $\xi$, and $u_{min}$, depending on $R{e}_D$. Transverse-oriented parameters ($W_w \mathrm{a}\mathrm{n}\mathrm{d} \eta$) vary non-monotonically. In addition, it is found that the streamwise locations of maximum wake width ($x_{w,max}$) and minimum velocity ($x_{u,min}$) are unaffected by the grooved cylinder configuration.

Tungsten inert gas (TIG) welding of AA5083 aluminum alloy is sensitive to heat input and shielding conditions, which can lead to defects such as porosity and burn-through that compromise weld quality. Conventional non-destructive testing methods are generally performed after welding and therefore provide limited capability for real-time process monitoring. This study presents an acoustic emission (AE)-based frequency-domain framework for real-time classification of weld conditions during TIG welding of AA5083. Acoustic signals were acquired at a sampling rate of 10 kHz and transformed into frequency-domain representations using the Fast Fourier Transform (FFT). Decision Tree (DT), Support Vector Machine (SVM), Artificial Neural Network (ANN), and ensemble-learning classifiers were evaluated using the resulting spectral features. To address the high dimensionality of the FFT representation, Principal Component Analysis (PCA) was incorporated into the modeling workflow, with the retained components determined from the model-development data. Five-fold cross-validation and grid-search-based hyperparameter tuning were used during model development, while an independent test set was reserved for final evaluation. The best-performing classifiers achieved a classification accuracy of approximately 0.99 for distinguishing good-weld, porosity, and burn-through conditions. Weld-condition labels were independently validated using visual inspection and radiographic testing. FFT and Short-Time Fourier Transform (STFT) analyses were used to characterize global and time-dependent spectral behavior, respectively, while SHapley Additive exPlanations (SHAP) were employed to identify frequency regions contributing to model predictions. A comparative analysis with time-domain statistical features further demonstrated the stronger discriminative capability of the FFT-derived representation under the investigated conditions. The proposed framework combines high classification performance with interpretable frequency-domain information and provides a basis for in-process weld-condition monitoring and quality control of TIG-welded AA5083.