Density Tagging Velocimetry, a novel optical technique for point-wise measurement of flow velocity is proposed here. This new method is based on the detection and subsequent tracking of a local density variation deliberately inserted in the flow. The experimental implementation comprising tagging, detection, and velocity evalution reverts to and combines principles of well-known optical measurement techniques. Density Tagging Velocimetry has the potential for inflight application and is particularly suited for measuring flow velocities in regions where the use of tracer particles is difficult or undesired. The applicability of this new technique is illustrated by a jet flow measurement. 1 Introduction Most common flow velocity measurement techniques in modern experimental fluid dynamics are optical methods that rely on the imaging and tracking of particles which have been added to the fluid-flow, e.g. Particle Image Velocimetry (PIV), Laser Doppler Velocimetry (LDV), and Light Detection and Ranging (LiDaR). The main advantage of these optical techniques compared to conventional velocity probes, e.g. hot wires and Pitot tubes, is their non-intrusiveness. However, finding adequate tracer particles that accurately follow the flow is challenging. Occasionally, we encounter situations where the use of tracer particles is difficult (e.g. in specialised wind tunnels or microchannels and during

This paper presents a nonlinear time-series analysis of the thermoacoustic instabilities of an experimental slot burner. The main objective was the calculation of indexes capable of detecting in advance the combustion instabilities by gradually increasing the flow Reynolds number of the pilot burner. A chaotic analysis based on diagonalwise measurements of the recurrence plots was performed on the basis of which the following indexes were calculated: the τ-recurrence rate index RRτ, the τ-determinism index DETτ, the τ-average diagonal line length index Lτ, and the τ-entropy index sτ. A quantification carried out by means of the standard deviation σ and mean values μ of the diagonalwise measurements showed that the aforementioned indexes were successfully able to sort all cases under analysis mainly into two groups: the first three cases that correspond to the stable regime named “Combustion Noise” and the remaining cases that were associated with the unstable regime called “Combustion Instability.” Additionally, the particle image velocimetry optical method was applied in order to compute a new index based on the velocity fields. The results showed that the index Vh, based on the local heights of the velocity profiles of the central flame, was also capable of detecting the same two groups previously identified by the nonlinear analysis. Nevertheless, the most sensitive indexes were the indexes RRτμ, DETτσ, and sτσ since these indexes were able to detect the transition between the combustion noise and combustion instability regimes. Therefore, the present results proved that the proposed five indexes were effective precursors in order to detect in advance the combustion instabilities.

This article presents a study of the early detection of combustion instabilities of a [Formula: see text] liquid rapid premixed oil swirled burner. The main objective was the calculation of indexes, based on a chaotic analysis, able to detect in advance the combustion instabilities. In the combustor, the air mass flow rate was kept constant, and in order to induce the combustion instabilities, the fuel mass flow rate was adjusted during the experiments in which pressure and radiant energy fluctuations were simultaneously measured from the combustion chamber. In this chaotic analysis, joint recurrence plots were calculated in order to analyze the dependence between the pressure and radiant energy fluctuations. Hence, a diagonal-wise quantification was applied to the joint recurrence plots to calculate four indexes: the τ-recurrence rate index [Formula: see text], the τ-determinism index [Formula: see text], the τ-average diagonal line length index [Formula: see text], and the τ-entropy index [Formula: see text]. The results show that all four indexes were capable of sorting all cases under analysis into two groups: the “combustion noise regime” due to the low-amplitude aperiodic oscillations and the “combustion instability regime” due to the high-amplitude periodic oscillations. In addition, early detection of the transitions were also detected. Therefore, the results presented in this research showed that the four indexes were effective precursors in order to detect in advance the combustion instabilities.

Recent studies have shown that the use of winglets in aircrafts wing tips have been able to reduce fuel consumption by reducing the lift-induced drag caused by wing tip vortex. This paper presents a 3-D numerical study to analyze the drag and lift forces, and the behavior of the vortexes generated in the wing tips from a modified commercial Boeing aircraft 767-300/ER. This type of aircraft does not contain winglets to control the wing tip vortex, therefore, the aerodynamic effects were analyzed adding two models of winglets to the wing tip. The first one is the vortex diffuser winglet and the second one is the tip fence winglet. The analyses were made for steady state and compressible flow, for a constant Mach number. The results show that the vortex diffuser winglet gives the best results, reducing the core velocity of the wing tip vortex up to 19%, the total drag force of the aircraft up to 3.6% and it leads to a lift increase of up to 2.4% with respect to the original aircraft without winglets.