Undergraduate
Thesis

Design and Analysis of a Bladeless Air Jet Windscreen Wiper System

Supervisor: Dr. Md. Ehsan, Professor, Department of Mechanical Engineering, BUET

TImeline: May 2022 – May 2023

Introduction

This thesis addresses the limitations of traditional wiper systems in heavy rain, which often impair driver visibility due to repetitive motion. It explores the development of a new wiper system capable of effectively clearing water from the windshield without disrupting the driver’s view, even in intense rainfall.

Research focused on qualitative testing, with various nozzles designed and fabricated to assess rain removal effectiveness. Rainfall conditions were modeled to simulate moderate and heavy rain, and the power consumption of wiper motors and compressors was analyzed for efficiency.

Findings indicate that the proposed system can remove rain effectively without visual disturbance; however, further optimization of nozzle design and compressor efficiency is essential for enhanced performance and energy savings. In conclusion, the study demonstrates the feasibility of the new wiper concept but highlights the need for continued refinement.

Methodology

Rain Modeling

The methodology involved simulating rain using a brass nozzle with adjustable diameter to control droplet size and distribution. To measure raindrop diameter, the stain method was used by marking spots on filter paper and measuring them, with calibration for accuracy. Raindrop intensity was measured by collecting rain in a funnel of known diameter and recording the accumulated volume in a cylinder over a specified time. This volume was converted to mm/h by extrapolating a short measurement period to a one-hour equivalent.

Nozzle Fabrication

In the second phase of windshield testing, two types of brass nozzles were designed and fabricated: a multiple hole nozzle with three holes for targeted jets and a flat jet nozzle with rectangular slots for wider coverage. Brass T-joints (¼ inch) were sourced and modified at BUET’s machine shop. The multiple hole nozzle was drilled using a milling machine, while the flat jet nozzle slots were cut using various milling cutters (T235S, T435S, T403S) and a hacksaw for precision. End holes were sealed through brazing in the welding shop.

Experimental Analysis

An experimental setup was developed to test the fabricated nozzles under improved conditions using a full-scale CNG windshield stabilized by a V frame. A nozzle assembly facilitated the experiments, and enhanced rain modeling was employed to simulate realistic rainfall. The tests included: measuring the coverage area by blowing air through a sand bed, evaluating the nozzles with the modeled rain and setup parameters, and measuring the velocity of the T235S nozzle, which showed the best performance, to determine the required velocity for effective windshield cleaning.

Results

Rain Modelling

The study modeled rainfall with specific parameters: moderate rainfall at 15mm/h and heavy rainfall at 28mm/h. The median raindrop diameter was 1.28mm for moderate and 2.21mm for heavy rainfall. The stain method was unsuitable for measuring drops under 1.0mm, so light rain couldn't be accurately modeled. Calibration was performed, and experimental data were validated against established datasets, revealing discrepancies primarily in the light rain region due to measurement limitations.

Nozzle Performance Analysis

The research evaluated airflow performance using sand tests on nozzles at 3 bar gauge pressure during moderate rainfall. The T411S nozzle covered the widest area, while the T235S nozzle balanced both width and length coverage. In the final test, most nozzles produced a central water line, making the surface opaque, except for T313S, T53H, and T235S. The T235S nozzle performed best, effectively clearing the windshield at 30 psi and an air velocity of 17.85 m/s.

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