Effect of Operating Conditions, Lobe-number, Clearance Size and Rotor Profile on the Transient Hydrodynamics, Heat Interaction, and Performance of a Root Blower

Abstract

Attempt is made to capture the unsteady internal flow phenomena and heat interaction in a root blower and to comprehend the effect of main influencing factors on the performance of the blower using transient numerical simulation through adaptive mesh redistribution (i.e. Moving Mesh Method) technique. A grid independence test is conducted to decide the size of grid for the numerical simulation. Validation of the adopted methodology is made using the results available in literatures (Li et al., 2013). At first, effort is made to apprehend the effect of operating conditions (rotor speed and discharge pressure) on the unsteady fluid flow and heat transfer characteristics. Then, the influence of number of lobes per rotor (2-lobe, 3-lobe, 4- lobe) on the transient hydrodynamics and heat interaction in the blower is studied. Next, the influence of clearance size (provided in between the rotors or in between the rotor and casing) on the said flow field and heat interactions is examined. Finally, the profile geometry of the rotors of the blower is parametrized and an attempt is made to establish a relationship between the shape of the rotor profile and the performance of the root blower using multiple regression analysis and neural network with parametric study or Genic Algorithm (GA). Spatial distribution of pressure, velocity magnitude, velocity vector, stream function, and temperature, throughout the flow domain are extracted at each instant of time to meet the objectives. For better understanding, time variation of area weighted average velocity magnitude, mass flux and temperature at the exhaust port are also evaluated. The variation of discharge velocity and mass flow rate with time is found to be fluctuating in nature. It is found that internal pressure & velocity distribution within the blower, reverse flow at the inlet or backflow at the outlet, vorticity in the flow domain, temperature rise in the flow domain, nature of time variation of exhaust velocity, mass flow rate and temperature are strongly depended on the chosen rotor speed, discharge pressure, clearance size in between two rotors or in between rotor & casing. They are also found to be very sensitive to the number of lobes used to define the rotor profile and the shape of the rotor profile. The shape of the rotor profile of a 2-lobe rotor is successfully parametrized by two independent parameters (base and waist circle radius). The complex non- linear relationship between the performance of the root blower (in terms of discharge mass flux) and the shape of the rotor profile (in terms of base and waist circle radius) is perfectly captured by the indigenously developed hybrid methodology (obtained through the combination of the local search algorithm: backpropagation and the global search tool: GA) using ‘C’ programming language in ‘Unix’ operating system