Effect of initial conditions on mean flow characteristics of a three dimensional turbulent wall jet

The effect of initial conditions in a [Formula: see text] sidewall enclosure on the mean flow characteristics of a three dimensional turbulent square wall jet has been studied experimentally. The initial conditions are varied by varying the length of the nozzle; it is varied as l/ h = 10, 50, and 90, where l and h indicates the nozzle length and the side of the square nozzle, respectively. The effect of nozzle length on initial velocity profiles, velocity distribution in lateral and wall normal directions, spread rate, decay of maximum mean velocity, local Reynolds number and similarity behaviour has been studied. The wall normal spread width is higher for the nozzle length l/h = 10 in the near field [Formula: see text] but this trend completely changed after [Formula: see text]. The spread rate is found independent of the initial condition of the nozzles in the fully developed region. The decay rate of maximum mean velocity is found higher for l/ h = 10 in the region of ([Formula: see text], whereas decay rate becomes independent of the initial conditions in the fully developed region [Formula: see text]. The local Reynolds number variation is also estimated along the downstream directions for present case and found that the local Reynolds number [Formula: see text] reaches approximately 56% of the jet exit Reynolds number [Formula: see text] at [Formula: see text] for nozzle length l/ h = 10, while it is 57% and 59% of Rejet for the nozzles [Formula: see text] and [Formula: see text] respectively at the same location. The nozzle l/ h = 10 attained self similar behaviour more quickly as compared to the other nozzles. The sidewall played a significant role which pushed the fluid more towards the center resulting in a lower jet half width in the wall normal direction as compared to the corresponding case, without a sidewall. The decay rates of the maximum mean velocity for all the nozzles are estimated to be 1.08 which is in the accepted range found in the literature.

Structure Optimization Design of Pulseoscillation Amplifier for Hydraulic Oscillator Based on Numerical Simulation

Hydraulic oscillator is one of the effective tools to solve the problem of high friction in directional drilling and horizontal drilling. However, there are some problems with this kind of tools such as high pressure loss and insufficient vibration force. Because of its self-excited oscillation characteristics, pulse oscillation amplifier can realize the amplification of pulse jet pressure under the condition of lowpressure loss, which is one of the effective ways to solve the above problems of hydraulic oscillator. In this paper, according to the working characteristics of hydraulic oscillator and the demand of pulse amplification, the structure of pulse oscillator amplifier was optimized based on numerical simulation method. Firstly, the geometric and numerical models of the pulse oscillator amplifier were constructed, and the flow field distribution and pulse amplification effect of the pulse oscillation amplifier under different structural parameters were simulated and analyzed, and the influence of different structural parameters on the pulse amplification effect was explored. Secondly, the structure of the pulse oscillator amplifier was optimized by Response Surface Method, and the optimal structure based on the effect of outlet pressure amplification was obtained: upper nozzle diameter D1=22mm, upper nozzle length L1=26mm, lower nozzle diameter D2=28mm, lower nozzle length L2=28mm, cavity length L=58mm, cavity diameter d=80mm, angle 60°. Its pressure loss was 0.3MPa and outlet pressure peak value was 4.5MPa, which was 1.8 times of the inlet pressure peak value of 2.5MPa. Finally, the minimum relative error between the experimental results and the numerical simulation results was 4%, which has verified the credibility of the numerical simulation and structural optimization results.

Capabilities and Limitations of Fire-Shaping to Produce Glass Nozzles

Microfluidic devices for drop and emulsion production are often built using fire-shaped (or fire-polished) glass nozzles. These are usually fabricated manually with inexpensive equipment. The shape limitations and poor reproducibility are pointed as the main drawbacks. Here, we evaluate the capabilities of a new fire-shaping approach which fabricates the nozzle by heating a vertical rotating capillary at the Bottom of a Lateral Flame (BLF). We analyze the effect of the heating conditions, and the capillary size and tolerances. The shape reproducibility is excellent for nozzles of the same size produced with the same conditions. However, the size reproducibility is limited and does not seem to be significantly affected by the heating conditions. Specifically, the minimum neck diameter standard deviation is 3%. Different shapes can be obtained by changing the heating position or the capillary dimensions, though, for a given diameter reduction, there is a minimum nozzle length due to the overturning of the surface. The use of thinner (wall or inner diameter) capillaries allows producing much shorter nozzles but hinders the size reproducibility. Finally, we showed an example of how the performance of a microfluidic device is affected by the nozzle shape: a Gas Dynamic Virtual Nozzle (GDVN) built with a higher convergent rate nozzle works over a wider parametric range without whipping.

Numerical Analysis of Fuel Injector Nozzle Geometry - Influence on Liquid Fuel Contraction Coefficient and Reynolds Number

This paper investigates the influence of the fuel injector nozzle geometry on the liquid fuel contraction coefficient and Reynolds number. The main three fuel injector nozzle geometry parameters: nozzle diameter (d), nozzle length (l) and nozzle inlet radius (r) have a strong influence on the liquid fuel contraction coefficient and Reynolds number. The variation of the nozzle geometry variables at different liquid fuel pressures, temperatures and injection rates was analyzed. The liquid fuel contraction coefficient and Reynolds number increase with an increase in the nozzle diameter, regardless of the fuel injection rate. An increase in the r/d ratio causes an increase in the fuel contraction coefficient, but the increase is not significant after r/d = 0.1. A nozzle length increase causes a decrease in the fuel contraction coefficient. Increase in the nozzle length of 0.5 mm causes an approximately similar decrease in the contraction coefficient at any fuel pressure and any nozzle length. Fuel injectors should operate with minimal possible nozzle lengths in order to obtain higher fuel contraction coefficients.

К ВОПРОСУ ТЕРМОДИНАМИЧЕСКОГО ПРОЕКТИРОВАНИЯ КАМЕРЫ ЖРД

Analysis of the thermodynamic and thermophysical properties of combustion products (CP) in the liquid rocket engine (LRE) chamber shows that their dissociation degree depends on temperature T, gas expansion degree ε, etc. Practically, CP’s are always chemically active working fluid, therefore the number of moles N of the products varies along the length of the LRE chamber in the entire reaction mixture. The local values of the parameters T and N depend on the specific physical conditions. Therefore, the distribution of local numbers of moles of the components of the gas mixture and its heat capacities can be represented as dependencies N~f(T) and c~g(T). For this purpose based on the numerical values of the moles and the heat capacities of the gas mixture components in the main sections of the LRE chamber are formed as corresponding empirical functions through interpolation. Analysis of changes in moles and weight fractions of gaseous and condensed СP’s components shows that, depending on the specific conditions (α, Km, pc, ε), the number of moles of one group of individual substances increases, while these parameters of the other group decrease. These changes are alternating in nature and lead to the formation of new centers -sources of chemical and thermal energy along the length of the LRE nozzle. Thus, for different conditions (α, Km, pc, ε), the design of the LRE chamber should be carried out taking into account the nature of the change in N, cp, cv, and γ. Therefore, from energy conversion, the number of moles of the i-th CP component can be represented as a function Ni = f(Ti) or Ni = f(x,y). Numerical studies show that, based on the Ni values in the main sections of the LRE chamber with a given length, it is possible to form linear or nonlinear empirical functions in the form Ni= f(x) by interpolation. Depending on the specific tasks, one of the interpolation functions can be taken into account in the formulas for calculating the specific heats of CP. In this case, to form the refined geometry of the LRE chamber, the thermo-gas-dynamic calculation is repeated taking into account new indicated dependencies. Consequently, the system of equations for the thermodynamic calculation of an LRE is solved taking into account new functions. This approach allows forming the optimal contour of the LRE chamber at the preliminary stage of engine design and improving the results of gas-dynamic calculation and profiling of the nozzle using a modified method of characteristics. In the framework of the presented studies, to obtain an optimal geometry for the LRE nozzle, are compared values of the velocities, which obtained using the solutions of the direct and inverse problems. Thus, the correct consideration of changes in the basic parameters along the nozzle length allows us to organize the correct operation of the LRE chamber by changing the thermal properties of CP along the nozzle length in all flight conditions of the flight vehicle. This circumstance requires some improvement of the principles and schemes of regulation systems of the LRE operation, which leads to the conduct of extensive researches in this direction.