Straight-walled Diffusers Research Articles

Design and numerical study of active cooling system of measurement while drilling for high temperature based on supersonic

Measurement while drilling (MWD) plays an important role in controlling well trajectory, improving drilling efficiency and saving drilling cost. In recent years, a large number of high-temperature wells have appeared, which makes the traditional MWD instruments no longer applicable. So far, no active cooling method has been successfully applied to MWD instruments for high-temperature oil and gas wells. This paper presents a new active cooling method for air drilling by utilizing the throttling and cooling of drilling gas, and the cooling system is designed. An axisymmetric numerical model of internal fluid is established, and different drilling gas flow channel design methods are discussed. The research results indicate that the wall temperature of the cooling section is much higher than the center fluid temperature, but lower than the ambient temperature, and can be used for active cooling of downhole drilling instruments. Compared with other design methods, the supersonic nozzle designed using the Bezier method has better parallelism of the gas in cooling section. The diffusion capability of straight wall diffuser is better than that of curved wall diffuser, and it can withstand greater back pressure. For straight wall diffuser, increasing the throat length and reducing the contraction and expansion angle can improve the diffusion capacity, but they also lead to a longer diffuser.

FLOW PERFORMANCE COMPARISON ALONG THE CENTERLINE IN STRAIGHT AND S-SHAPED DIFFUSER

In this paper of the S-shaped diffuser with area ratio (AR) 1.5, an experimental investigation was conducted to analyze the effect of the change in curvature of a straight-wall diffuser. During this study, a Straight diffuser was changed in to a curved diffuser at different angles as their same upper and lower limbs (60/60, 90/90). Profile equations of diffusers were generated with the help of MATLAB/Simulink v2017a software. In this work centerline length is constant for all three profiles, Centerline length that’s utilized in the sector of circle and radius of curvature is calculated. S-shaped diffuser had a different unique angle with square inlet and a rectangular outlet. S-shaped diffuser CPR and CTL results compared with a straight walled diffuser with the different inlet velocity and Reynolds Number. These outcomes from this research obtained the coefficient of static pressure gain and coefficient of total pressure loss for the three profile of the diffuser (Straight, 60/60, and 90/90 S-Shaped Diffuser).

Design and Performance of an Improved Trapped Vortex Combustor

A trapped vortex combustor (TVC) has been a very promising novel concept for it offers improvements in lean blow out, altitude relight, operating range, as well as a potential to decrease NOx emissions compared to conventional combustors. The present paper discusses the improved designs of the new combustor over the prior ones of our research group, including that: a) the overall dimensions, both axial and radial, are reduced to those of an actual aero-engine combustor; b) the air flow distribution is optimized, and especially 15 (of the air is fed into the liner as cooling air; c) a straight-wall diffuser with divergence angle 9°is added. A series of experiments (cavity-fueled only, under atmospheric pressure) has been conducted to investigate the performance of the improved TVC. Experimental results show that at the inlet temperature of 523 K, the inlet pressure of 0.1 MPa, stable operation of the TVC test rig is observed for the Mach number 0.15–0.34, indicating good flame stability; the combustion efficiency obtained in this paper falls into the range of 60%−96% as the total excess air ratio increases, the combustion efficiency decreases, while the increase of the inlet temperature is beneficial to high combustion efficiency; besides, the optimal Mach numbers for high combustion efficiency under different inlet conditions are confirmed. The outlet temperature profiles feature a bottom in the mid-height of the exit. This paper demonstrates the feasibility for the TVC to be applied to a realistic aero-engine preliminarily and provides reference for TVC design.

Three-Dimensional Flow Measurements in Conical and Straight Wall Centrifugal Compressor Vaneless Diffusers

In the current work three-dimensional flow measurements in two types of centrifugal compressor vaneless diffuser were obtained using hot wire anemometry. The first diffuser was conical, designed to give a constant flow area, while the second straight wall diffuser had a constant axial width. Measurements of mean velocity, flow angle and velocity fluctuation level were obtained on eight cross-sectional planes in each diffuser. The jet-wake flow pattern and the impeller blade wakes are clearly visible at the inlet of both diffusers. Mixing out of the blade wake proceeds more rapidly in the straight diffuser. The hub boundary layer also develops more rapidly in this diffuser because of the adverse pressure gradient. Velocity fluctuation level measurements highlight the mixing regions within the diffusers. Recommendations are also made for the design of vaned diffusers. A larger vaneless space would be required with a straight wall diffuser and significant twisting of the vane would be required for both diffuser geometries if significant incidence losses are to be avoided.

Calculation of Laminar Separated Flow in Symmetric Two-Dimensional Diffusers

This study is concerned with numerical analysis of laminar separated flow in symmetric, two-dimensional, straight-walled diffusers. With Reynolds numbers Re = 56 and 114 and expansion ratios ER = 3 and 4, totally, there are four cases considered. At the low Reynolds number and the low expansion ratio the flow in the diffuser is nearly symmetric to the center line, irrespective of the diffusion angle. As Reynolds number or expansion ratio increases, a large recirculation region forms at one side wall and a small one at the other side. For the case with Re = 114 and ER = 4 the small recirculating flow disappears at small diffusion angles and a third recirculating flow appear in the same side of the small main recirculation region for large diffusion angles. The pressure recovery reaches its peak value somewhere downstream of the reattachment point of the large recirculating flow. The effectiveness of the diffuser deteriorates as the diffusion angle increases, apart from that at Re = 56 the effectiveness increases from θ = 15 to 30 deg. Symmetric flow solutions can be obtained by incorporating a symmetric relaxation method. The pressure recovery is higher for the symmetric flow than that for the asymmetric flow owing to the weaker recirculating strength in the former.

Analysis of Subsonic Transitory Stalled Flows in Straight-Walled Diffusers

A simple, semi-empirical procedure is presented for computation of subsonic, turbulent, attached, and transitory-stalled flows in straight-walled diffusers with plenum exit. The procedure employs a zonal model while using the concept of a dividing streamline and integral methods for boundary layer calculations on diverging and parallel side walls. The dividing streamline separates the transitory stall zone, having zero mass flow rate, from the effective flow channel. The procedure predicts the pressure as a function of streamwise location with modest computation times, typically a few minutes on a personal computer and can be useful in design calculations.

Flow Regimes in Two-Dimensional Ribbed Diffusers

Water table flow visualization tests of a straight wall diffuser and corresponding ribbed diffuser were conducted over a wide range of total divergence angles and diffuser length to throat width ratios. Rib parameters such as inter-rib cavity depth to width ratio, inter-rib cavity width, rib thickness, and number of ribs were varied, as well as rib contour. Motion pictures were obtained of the secondary flow patterns occurring within the inter-rib cavities, and hot film measurements were made to determine the extent of velocity fluctuations induced by the cavities. In general, the addition of ribs increased the no-appreciable stall regime.

The Design and Performance of Two-Dimensional, Curved Diffusers: Part I—Exposition of Method and Part II—Experiment, Evaluation of Method, and Conclusions

A procedure for the design of two-dimensional, curved diffusers is developed and evaluated through comparisons with flow regime and performance data. As input to the method, the inner and outer-wall potential-flow pressure distributions are specified as combinations of straight-wall diffuser pressure distributions. The diffuser shape is calculated using the method of Stanitz. In Part II criteria are established for choosing desirable inner and outer-wall pressure distributions. These criteria are based on systematic performance and flow regime tests carried out on curved diffusers with inner-wall length to throat width ratios between 4 and 10, area ratios between 1.5 and 2.1, and turning angles between 30 and 90 deg. The procedure yields diffusers of higher performance than circular-arc center-line diffusers.

Flow Regimes in Curved Subsonic Diffusers

An extension and refinement of the work of Moore and Kline (NACA TN 4080) is presented for the flow regimes found in straight-walled diffusers. A systematic map of flow regimes in curved diffusing passages is presented, in steps of ten degrees, for a range of flow turning angles from 0 to 90 degrees. Each curved diffuser geometry tested had a circular arc center line and a linear area distribution normal to the center line. The line of first appreciable stall showed a peak in divergence angle as a function of the ratio of center line length to throat width for all values of turning angle equal to, or greater than, fifty degrees. The divergence angle at the transition to the fully developed stall regime was found to decrease monotonically with increase in turning angle at fixed values of the ratio of center line length to throat width in all cases.

Closure to “Discussion of ‘Optimum Design of Straight-Walled Diffusers’” (1959, ASME J. Basic Eng., 81, pp. 329–330)

Closure to “Discussion of ‘Optimum Design of Straight-Walled Diffusers’” (1959, ASME J. Basic Eng., 81, pp. 329–330)